{
 "name": "IB Physics IA ideas",
 "author": "Pietro Meloni",
 "url": "https://www.pietromeloni.com/ib-ia-ideas/physics",
 "updated": "2026-09-26",
 "count": 300,
 "ideas": [
  {
   "id": "launch-angle-and-range-with-a-calibrated-launcher",
   "topic": "A.1",
   "topicName": "Kinematics",
   "level": "both",
   "title": "Launch angle and range with a calibrated launcher",
   "researchQuestion": "How does the horizontal range of a steel ball fired from a spring launcher at 15° to 75° in 5° steps compare with the ideal prediction, allowing for launch height?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 5,
   "independentVariable": "Launch angle, 15° to 75° in 5° steps (13 values), with 5 shots per angle.",
   "dependentVariable": "Landing point on carbon paper over white paper, read with a metre rule. The launch speed is found separately with light gates or from a video of a horizontal shot. Range compared with the calculated theoretical range.",
   "controlledVariables": "Same launcher setting and spring compression, so speed stays fixed and is checked at several angles. Launch height measured and kept the same. Same ball mass. Landing surface at a fixed height, or the height difference corrected in the theory.",
   "physicsNeeded": "For launch and landing at the same height R = v² sin 2θ / g. With a launch height h, R = (v cos θ / g)(v sin θ + √(v² sin²θ + 2gh)). Plot R against sin 2θ for a near-linear graph when h is small; the gradient is v²/g. Compare the angle of maximum range with 45°.",
   "slVsHl": "SL students plot R against sin 2θ and find v from the gradient. To reach the top band, include launch height in the model and show why the best angle is below 45°, with residuals against the model. HL can add air resistance in a numerical simulation.",
   "whereMarksAreLost": "Research design: launch speed changing with angle, or with the launch height ignored. Data analysis: only checking the maximum, with no fit. Conclusion: saying it proves 45° with no comparison of the data with the model. Evaluation: angle reading error and air resistance not discussed.",
   "dataNote": "Needs a spring launcher, carbon paper, a ruler and a protractor; the launch angle reading (about ±1°) and speed variation are the main uncertainty.",
   "verdict": "Overdone (listed on 5 sites) and easily seen as a textbook exercise. Only worth it if you test the model with launch height and speed checks, or use the fitted speed to challenge the ideal model."
  },
  {
   "id": "deceleration-of-a-rolling-ball-on-different-surfaces",
   "topic": "A.1",
   "topicName": "Kinematics",
   "level": "both",
   "title": "Deceleration of a rolling ball on different surfaces",
   "researchQuestion": "How does the surface roughness, measured as the grit number of sandpaper from 60 to 400, affect the deceleration of a steel ball rolling on a horizontal board?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Surface, given by sandpaper grit: 60, 80, 120, 240, 320, 400, plus smooth board (7 values). Each is tested with 5 rolls, launched from a ramp release height that is kept fixed.",
   "dependentVariable": "Position against time of the ball, from a phone video at 240 fps, analysed frame by frame in software such as Tracker. Deceleration is the gradient of a velocity against time graph, taken from the same clip.",
   "controlledVariables": "Same ball and same release point on a ramp, so that starting speed is the same. Board levelled with a spirit level. Same length of surface in the field of view. Air temperature and humidity are not expected to change, but the same dust-free surface is used each time by replacing the sandpaper.",
   "physicsNeeded": "For constant deceleration a, v = u − a t, so the gradient of the v against t graph gives −a. Rolling resistance force is F = C_rr × m g, so a = C_rr g and the coefficient can be found for each surface. Plot a against grit number, or C_rr against average particle size.",
   "slVsHl": "SL: find a for each surface from velocity time graphs and describe how it changes with grit. Top band: convert to C_rr, check that a is constant along the run, and discuss whether roughness is a suitable numerical measure. HL depth is not needed, though the energy view with rotational kinetic energy can be added.",
   "whereMarksAreLost": "Research design: surface roughness described only qualitatively, or grit numbers used with no justification. Data analysis: assuming a constant deceleration without checking it. Conclusion: overstating the pattern from small differences. Evaluation: ignoring that a ball may slip at the start, and small board tilts.",
   "dataNote": "Needs a ramp, steel ball, sandpaper of various grits, a phone at high frame rate and free tracking software; the main uncertainty is a small tilt of the board.",
   "verdict": "Good as long as roughness gets a number, such as grit or a measured particle size. Twist: add a second, varied normal force by using balls of different mass, and test whether C_rr is truly independent of load."
  },
  {
   "id": "does-measured-g-depend-on-release-height",
   "topic": "A.1",
   "topicName": "Kinematics",
   "level": "both",
   "title": "Does measured g depend on release height?",
   "researchQuestion": "How does the release height of a steel ball, from 0.40 m to 2.00 m in steps of 0.20 m, affect the value of g calculated from its fall time?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Release height from 0.40 m to 2.00 m in 9 values, each repeated 5 times, measured with a metre rule or tape and a plumb line.",
   "dependentVariable": "Fall time with an electromagnet release and a trapdoor switch or light gate timer, then g = 2h/t² calculated for each height. Alternatively, video analysis at 240 fps.",
   "controlledVariables": "Same steel ball of one diameter and mass; same release mechanism to avoid initial speed; height measured from the bottom of the ball to the trap; room conditions unchanged.",
   "physicsNeeded": "For constant acceleration, h = ½gt², so plot h against t² and check that the gradient is g/2 with a straight line through the origin. With drag, g_apparent falls slowly with height. Plot g against h and look at residuals for a trend beyond the error bars.",
   "slVsHl": "An SL student can plot h against t², find g and compare with 9.81 m/s². Top band work checks the residuals and a fit with an offset, and models drag to predict the expected size of any systematic drift.",
   "whereMarksAreLost": "Research design: only 3 heights, so no meaningful trend can be seen. Data analysis: g averaged without checking for the trend, and uncertainty in t not propagated. Conclusion: claiming a dependence on height when the difference lies within the error bars.",
   "dataNote": "Needs an electromagnet timer or light gates; a steel ball's drag effect is under 0.1% at 2 m, so timing precision to 1 ms is needed to see any drift.",
   "verdict": "Good if you accept that the honest answer may be no measurable dependence, and then say so with numbers. The residual analysis makes the difference between an average and a top mark."
  },
  {
   "id": "golf-ball-flight-with-drag-from-video-tracking",
   "topic": "A.1",
   "topicName": "Kinematics",
   "level": "both",
   "title": "Golf ball flight with drag from video tracking",
   "researchQuestion": "How does the horizontal range of a golf ball launched at angles from 15° to 60° compare with a model with no air resistance and one including quadratic drag?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Launch angle from 15° to 60° in 5° steps, eight values, with three launches at each angle using a fixed launcher speed.",
   "dependentVariable": "Ball positions from slow motion video filmed with a phone against a metre grid, analysed with Tracker software. Calculate range and peak height, then compare with modelled values.",
   "controlledVariables": "Same launcher setting (a spring loaded launcher or a fixed ramp release) so the speed is measured and fixed. Same ball and same room with no draughts. Camera placed on a tripod perpendicular to the flight. Launch height kept constant.",
   "physicsNeeded": "With no drag, R = v² sin 2θ / g. With drag, integrate numerically in a spreadsheet using a = −kv v. Plot range against angle for the data and both models, and compare the residuals.",
   "slVsHl": "SL can compare the data with the no-drag model and find where it fails. A top answer builds a step by step numerical model with a fitted drag constant and says how well it works. HL depth could add the Magnus effect from backspin.",
   "whereMarksAreLost": "Research design: the question is vague about which models are compared and how the launch speed is set. Data analysis: no uncertainties in the position from video and not measuring the launch speed. Evaluation: not addressing lens distortion and the camera angle.",
   "dataNote": "Needs a launcher, a phone camera at 120 fps or more, and Tracker; the main uncertainty is calibration and parallax in the video.",
   "verdict": "Only a real idea once the models and how to test them are fixed, as usually stated online it is too vague. Best done indoors with a table tennis or golf ball and a numerical model."
  },
  {
   "id": "launch-angle-and-range-of-a-golf-ball-from-a-putter-or-wedge",
   "topic": "A.1",
   "topicName": "Kinematics",
   "level": "both",
   "title": "Launch angle and range of a golf ball from a putter or wedge",
   "researchQuestion": "How does the launch angle θ (10°, 20°, 30°, 40°, 50°, 60°, 70°) of a golf ball fired by a spring or pendulum launcher affect its horizontal range, in m, when launched from the same height?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Launch angle, 7 values from 10° to 70°, set with a protractor or an angle scale on a spring launcher. 5 shots per angle.",
   "dependentVariable": "Horizontal range from a tape measure with sand or carbon paper to mark landings, and the launch speed from video analysis in Tracker to compare with theory.",
   "controlledVariables": "Launch speed: same spring compression or same pendulum release height each shot. Launch height: launcher on the floor or measured above the landing level. Ball: the same golf ball, kept clean. Wind: indoors or in a still sports hall.",
   "physicsNeeded": "With no drag and equal heights R = v² sin2θ / g. Plot R against sin2θ: a line through the origin with gradient v²/g, so v can be found and compared with the video value. The maximum should be at 45°, but drag and launch height shift the best angle a little lower, which can be explained.",
   "slVsHl": "SL: show R against sin2θ and identify the best angle. Top band: a launch speed check by video, drag correction, and a simulation of the trajectory with drag to explain a peak below 45°.",
   "whereMarksAreLost": "Research design: a real golf club is impossible to keep at a set speed, so the launcher is a must. Data analysis: identical repeats show spread from ball spin. Conclusion: saying the peak is at 45° without evidence of the shape. Evaluation: ignoring the height offset and drag.",
   "dataNote": "A launcher, tape measure and protractor are enough; the main uncertainty is angle setting and launch speed consistency.",
   "verdict": "Very standard projectile work, so it will look ordinary unless you add drag modelling or a real launch height. Personalise by using the golf ball of a sport you play and testing the model in Tracker."
  },
  {
   "id": "measuring-g-from-a-falling-ball-s-impact-speed",
   "topic": "A.1",
   "topicName": "Kinematics",
   "level": "both",
   "title": "Measuring g from a falling ball's impact speed",
   "researchQuestion": "What value of g results from measuring the speed of a steel ball with a light gate after it falls from heights between 0.20 m and 1.20 m?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Drop height h, 6 values from 0.20 m to 1.20 m in 0.20 m steps, 5 drops each.",
   "dependentVariable": "Speed at the bottom from a light gate reading the transit time of the ball, v = d/t, using the ball diameter measured with a micrometer. g comes from the graph of v^2 against h.",
   "controlledVariables": "Same steel ball, with its diameter and mass recorded. Release by electromagnet or a thread cut to avoid an initial push. Light gate positioned just above the floor, at the same place for all drops. Ball passes through the centre of the beam.",
   "physicsNeeded": "Energy conservation gives 1/2 m v^2 = m g h, so v^2 = 2 g h. Plot v^2 (y) against h (x): gradient = 2g. Air resistance makes the gradient slightly lower.",
   "slVsHl": "SL students get g with an uncertainty and a percentage difference from 9.81 m/s^2. Higher marks come from correcting for the finite gate width (speed is the mean over the ball's diameter) and estimating the effect of drag. HL depth can include a drag model.",
   "whereMarksAreLost": "Research design: no way to release the ball without imparting speed. Data analysis: ignoring the height offset (measuring from the bottom of the ball vs the gate). Evaluation: not testing whether the systematic offset is in the intercept.",
   "dataNote": "Needs a light gate with timer, ball, clamp stand and metre rule; main uncertainty is the position of the beam and the timer resolution.",
   "verdict": "Precise and clean but heavily used, so treat it as a test of method. Worth it only if you add a real twist, such as quantifying drag with a light ball versus a heavy one."
  },
  {
   "id": "projectile-drag-from-tracked-video-trajectories",
   "topic": "A.1",
   "topicName": "Kinematics",
   "level": "both",
   "title": "Projectile drag from tracked video trajectories",
   "researchQuestion": "How does the frontal cross-sectional area of a light projectile (discs of diameter 2.0 to 10.0 cm, 5 values, equal mass) affect the drop in its horizontal range compared with the vacuum prediction, at a fixed launch speed of about 5 m/s?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Frontal area of a card or foam disc, from 3 to 80 cm² using 6 diameters, each launched at least 5 times.",
   "dependentVariable": "Video of each flight at 240 fps filmed with a phone against a metre scale, digitised in Tracker. The measured range is subtracted from the no-drag range calculated from the measured launch velocity, giving a range deficit in cm.",
   "controlledVariables": "Launch speed: use the same spring launcher compression and check the speed from the first frames. Mass: add plasticine to equalise. Launch angle: fixed with a clamped protractor. Shape and surface: same material cut to size.",
   "physicsNeeded": "Vacuum motion has x = v cosθ t and y = v sinθ t − ½gt². Drag F ≈ ½CρAv² is expected to make the range deficit grow with A. Plot range deficit against A and test for a straight line through the origin. Its gradient links to C and ρ, which can be compared with a literature value.",
   "slVsHl": "SL students can plot deficit against area and comment on proportionality. To reach top band, fit a numerical model with drag in a spreadsheet and compare it to the tracked path. HL students can add the v² dependence by varying launch speed too.",
   "whereMarksAreLost": "Research design: launch speed drifts between shots and is never checked. Data analysis: deficit is a small difference of two large numbers, and its uncertainty is ignored. Evaluation: ignores that a flat disc tumbles in flight, so the drag coefficient changes.",
   "dataNote": "Needs a launcher, a phone camera and Tracker; the main uncertainty is launch speed repeatability and frame timing.",
   "verdict": "A good choice if you like video analysis and want something beyond a standard drop test. Use light discs, or the drag effect will vanish in your error bars."
  },
  {
   "id": "ramp-angle-and-the-time-for-a-block-to-slide-down",
   "topic": "A.1",
   "topicName": "Kinematics",
   "level": "both",
   "title": "Ramp angle and the time for a block to slide down",
   "researchQuestion": "How does the angle of an inclined plank, from 10° to 40° in steps of 5°, affect the time a wooden block takes to slide 0.80 m from rest?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Ramp angle: 10°, 15°, 20°, 25°, 30°, 35°, 40°, set from height and length using sin θ = h/L, 5 repeats each.",
   "dependentVariable": "Time over 0.80 m measured with two light gates, or a 240 fps video; acceleration calculated from a = 2s/t².",
   "controlledVariables": "Block mass and contact face, the same block with the same face down. Ramp surface, wiped and dried before each set. Release position, fixed by a stop at the start. Ramp length, fixed at 1.2 m.",
   "physicsNeeded": "a = g(sin θ − μk cos θ). Plot a against sin θ; if μk is constant the gradient is g cos-corrected. Better: plot a/cos θ against tan θ, giving gradient g and intercept −μk g. The block starts sliding only above the angle where tan θ = μs.",
   "slVsHl": "SL: plot a against sin θ, and find μk from the fit. Top band: linearise fully, compare g from the gradient with 9.81, and consider whether μk changes with speed. HL not needed.",
   "whereMarksAreLost": "Research design: only doing time against angle with no theory, and a range too small to see the curve. Data analysis: reaction time errors from hand timing. Evaluation: not discussing how μk varies over the surface.",
   "dataNote": "Plank, block, ruler and a stopwatch is enough but light gates or video reduce timing error; the angle from the height measurement gives ±0.3°.",
   "verdict": "A safe, common set-up; to stand out, use the linearisation to extract μk and g and comment on the block not moving below about 10° if it sticks."
  },
  {
   "id": "rolling-acceleration-on-different-surfaces-on-a-ramp",
   "topic": "A.1",
   "topicName": "Kinematics",
   "level": "both",
   "title": "Rolling acceleration on different surfaces on a ramp",
   "researchQuestion": "How does the surface covering a 1.0 m ramp at 10° affect the acceleration of a steel ball rolling down it, using six different surfaces?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Surface material glued on the ramp: bare wood, felt, sandpaper of two grades, carpet, and rubber mat, giving six surfaces with five runs each. Roughness described by measured rolling friction, not by an assumed coefficient.",
   "dependentVariable": "Acceleration from a = 2s/t² using a metre rule and video timing at 240 fps, or two light gates for speeds. Effective friction inferred by comparing with the ideal rolling value.",
   "controlledVariables": "Ramp angle: fixed with a protractor and checked with a clinometer app. Ball: the same steel ball, cleaned. Release point: the same mark, released without push. Ramp length and straightness: same rail throughout.",
   "physicsNeeded": "For a solid sphere rolling without slipping a = (5/7) g sin θ, about 0.85 m/s² at 10°. Rolling resistance lowers this. Plot measured a for each surface against the ideal value and find the deficit, then relate to a rolling resistance coefficient.",
   "slVsHl": "SL: compare accelerations and explain them with the ideal value. Top band: extract rolling resistance and test the rolling condition. HL: include moment of inertia and rotational energy, from rigid body mechanics.",
   "whereMarksAreLost": "Research design: surface described as a friction coefficient that was never measured. Data analysis: five runs but no uncertainty from timing at short distances. Evaluation: not spotting that a ball needs friction to roll at all, so more friction does not mean slower.",
   "dataNote": "Ramp, ball and phone video; short run times give large timing uncertainty, so use a longer ramp or video frames.",
   "verdict": "Accessible but the framing is misleading: friction is needed for rolling. Make it stronger by measuring rolling resistance and using HL rotational dynamics."
  },
  {
   "id": "ruler-drop-reaction-time-after-fatiguing-grip-exercise",
   "topic": "A.1",
   "topicName": "Kinematics",
   "level": "both",
   "title": "Ruler-drop reaction time after fatiguing grip exercise",
   "researchQuestion": "How does the reaction time, found from ruler-drop distance, change during 5 minutes of recovery after 60 seconds of gripping a hand dynamometer, tested at 0, 30, 60, 120, 180 and 300 s?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Time after fatiguing exercise: 0, 30, 60, 120, 180 and 300 s (6 values), with 10 drops per time. A resting baseline is measured on a separate day.",
   "dependentVariable": "Distance the ruler falls before it is caught, read on a 30 cm ruler. Reaction time t = √(2d/g) is calculated from it for each drop.",
   "controlledVariables": "Participant: one or two volunteers, same hand. Method: same ruler, dropped by the same person at random moments. Time of day: sessions done at the same hour. Exercise: same grip force, checked on a dynamometer.",
   "physicsNeeded": "Free fall from rest gives d = ½gt², so t = √(2d/g). Plot t (y) against time after exercise (x) and fit a recovery curve, or plot d (y) against t² (x) to check that g is recovered from the gradient ×2.",
   "slVsHl": "SL students calculate t and compare it with the baseline. Top band work models the recovery with an exponential curve, considers the resolution of the ruler and the anticipation effect, and does a statistical comparison of the means.",
   "whereMarksAreLost": "Research design: the physics is thin and the fatigue level is not measured. Data analysis: too few drops, means without uncertainty. Evaluation: learning effect making later drops faster.",
   "dataNote": "Needs a metre rule and a hand dynamometer; the main uncertainty is anticipation and the learning effect over repeated drops.",
   "verdict": "Physics content is light, so I would only pick it if you tie it firmly to kinematics and uncertainty analysis. Randomised drop timing is the twist."
  },
  {
   "id": "sail-area-and-starting-acceleration-of-a-fan-driven-trolley",
   "topic": "A.1",
   "topicName": "Kinematics",
   "level": "both",
   "title": "Sail area and starting acceleration of a fan-driven trolley",
   "researchQuestion": "How does the area of a card sail, from 50 cm² to 250 cm² in five steps, affect the initial acceleration of a low-friction trolley in a steady stream of air from a desk fan?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Sail area: 50, 100, 150, 200 and 250 cm², cut from one card sheet, 4 repeats each.",
   "dependentVariable": "Acceleration from the first 0.3 s of a 240 fps slow-motion video of the trolley beside a ruler, using s = ½at², or from the gradient of a velocity–time graph in video analysis software.",
   "controlledVariables": "Fan speed and distance from the sail, fixed by a mark on the bench and checked with an anemometer. Trolley mass, kept constant by adding plasticine to balance the mass of the sails. Track levelled with a spirit level. Sail height and orientation, fixed to face square-on.",
   "physicsNeeded": "Newton's second law with drag force F ≈ ½ρCdAv², so a = F/m if mass is constant. Plot a against sail area, expecting a straight line through the origin. Note that boat wording in the source is replaced by a trolley on a track, which is more controlled than water.",
   "slVsHl": "SL: linear graph and comparison of the gradient with the fan wind speed. Top band: estimate the drag coefficient from the gradient and discuss uneven airflow across large sails. HL adds nothing needed.",
   "whereMarksAreLost": "Research design: mass changes with sail size, and airflow is not uniform across the fan face. Data analysis: uncertainty in acceleration from few video points. Evaluation: wind speed falls off away from the fan and no anemometer map is given.",
   "dataNote": "Needs a phone with slow motion and a dynamics track; the main uncertainty is non-uniform fan flow and friction in the wheels.",
   "verdict": "A good choice with a trolley in place of a boat, which avoids hard-to-control water. The twist: map fan air speed across the sail plane first."
  },
  {
   "id": "time-step-size-and-accuracy-in-a-projectile-drag-model",
   "topic": "A.1",
   "topicName": "Kinematics",
   "level": "both",
   "title": "Time step size and accuracy in a projectile drag model",
   "researchQuestion": "How does the time step, from 0.001 s to 0.5 s, change the calculated range of a projectile with quadratic air drag compared with the smallest step?",
   "dataDifficulty": 1,
   "dataSource": "simulation",
   "sitesListingIt": 1,
   "independentVariable": "Time step in an Euler model, 6 to 8 values from 0.5 s down to 0.001 s, plus a repeat with a better method if time allows.",
   "dependentVariable": "Calculated range and maximum height from a spreadsheet or Python model; percentage difference from the smallest step result.",
   "controlledVariables": "Same launch speed and angle. Same drag coefficient and mass. Same gravitational field strength. Same stopping condition, ending at ground level with interpolation.",
   "physicsNeeded": "Equations of motion with F = mg and drag F = kv^2, stepped as a = F/m. For zero drag the analytic range v^2 sin(2 theta)/g is the check. Plot error against time step on log-log axes; the gradient shows the order of the method.",
   "slVsHl": "SL: show error shrinking with step and justify a step choice. Top band: compare with real launches filmed for the drag, and fit the drag coefficient. HL: add a second method and compare convergence.",
   "whereMarksAreLost": "Research design: no real measurement to test the model. Data analysis: no error measure. Conclusion: no link to physics. Evaluation: not discussing the model's assumptions such as constant drag coefficient.",
   "dataNote": "Needs only a spreadsheet or code; without real data the investigation tests the method, not nature, so add a video measured launch.",
   "verdict": "Fine as a modelling piece, but risky as a stand-alone since a simulation only checks itself. Twist: film a ping pong ball launch and fit its drag coefficient."
  },
  {
   "id": "video-analysis-of-a-jump-trajectory-as-projectile-motion",
   "topic": "A.1",
   "topicName": "Kinematics",
   "level": "both",
   "title": "Video analysis of a jump trajectory as projectile motion",
   "researchQuestion": "How well does the path of a jumping animal or person's centre of mass follow a parabola, and how does the fitted launch speed change with take off angle between 30° and 70°?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Take off angle of the jumper, five or more values from 30° to 70°, from several jumps each filmed, using a small toy or a person doing standing jumps.",
   "dependentVariable": "Position of a marker on the hip filmed with a phone at 120 fps against a metre grid and tracked in Tracker. Calculate the launch speed and the vertical acceleration from the fitted parabola.",
   "controlledVariables": "Camera fixed on a tripod at hip height and perpendicular to the plane of motion. Same person or object and same marker position. Same take off surface and grid scale in the plane of the jump. Same frame rate and lighting.",
   "physicsNeeded": "For projectile motion y = x tan θ − g x² / (2 v² cos² θ). Fit a parabola to y against x and extract g from the vertical motion, expecting 9.81 m s⁻². The horizontal velocity should be constant.",
   "slVsHl": "SL tracks the motion and shows the horizontal velocity is nearly constant and the vertical acceleration is close to g. A stronger answer compares the height and range with what the launch speed predicts, and considers energy in the jump. HL depth is not needed. I would not use a real horse as a source of data, since access is unrealistic.",
   "whereMarksAreLost": "Research design: the source idea has no measurable variable, and a real horse is not practical. Data analysis: tracking a limb rather than the centre of mass, and no uncertainty in the scale. Evaluation: perspective error from the camera not being perpendicular.",
   "dataNote": "Needs a phone, tripod and Tracker; the main uncertainty is the marker not following the centre of mass and the scale calibration.",
   "verdict": "As written it is not measurable, and a horse is out of reach for a school lab. Use a person, a toy or a rolling ball instead, or use published video of a horse only if the scale is known. The twist is to compare the centre of mass path with the foot path."
  },
  {
   "id": "falling-sphere-viscosity-of-honey-across-temperature",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Falling-sphere viscosity of honey across temperature",
   "researchQuestion": "How does the dynamic viscosity of honey, found from the terminal speed of a 3 mm steel ball, vary between 20 °C and 60 °C in 5 °C steps?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 5,
   "independentVariable": "Honey temperature, 20 to 60 °C in 5 °C steps (9 values), with 3 to 5 drops at each.",
   "dependentVariable": "Terminal speed from a video of the ball passing marked lines in a tall measuring cylinder, timed frame by frame. Viscosity calculated from Stokes' law with a buoyancy correction. Temperature read by a digital thermometer at mid-depth.",
   "controlledVariables": "Same honey batch and water content. Same ball diameter, checked with a micrometer, and released on the centre line. Cylinder wide enough that wall effects are small, or a wall correction applied. Timing only in the section where the speed is constant, checked from the video.",
   "physicsNeeded": "Stokes: F = 6πηrv. At terminal speed, 2r²g(ρs − ρl)/(9v) = η. Plot ln η against 1/T, which should be roughly linear, for an Arrhenius-type gradient. A plot of η against T alone is curved, which is a useful point to discuss.",
   "slVsHl": "SL students give η against T and explain the falling trend. Higher marks come from testing the Stokes assumptions (terminal speed reached, Reynolds number small, wall correction) and the linearised ln η against 1/T graph with activation energy. HL gives no extra syllabus, but it suits deeper error analysis.",
   "whereMarksAreLost": "Research design: honey not uniform in temperature after heating, or no check that terminal speed is reached. Data analysis: ignoring the uncertainty of the measured speed and ball diameter. Conclusion: claiming a trend without a quantitative fit. Evaluation: not addressing the temperature drift during a drop.",
   "dataNote": "Needs a tall cylinder, a water bath, a phone camera and a micrometer; honey cools quickly and can be non-uniform, which is the main uncertainty.",
   "verdict": "Overdone (listed on 5 sites), and honey or oil with temperature is what examiners expect. Make it your own by verifying Stokes' law assumptions or by fitting an Arrhenius model, not by only plotting a trend."
  },
  {
   "id": "acceleration-against-sin-on-a-friction-affected-ramp",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Acceleration against sin θ on a friction-affected ramp",
   "researchQuestion": "How does the acceleration of a dynamics trolley change as a track is tilted from 3° to 20°, and does the intercept on an a against sin θ graph reveal a rolling resistance force?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 4,
   "independentVariable": "Track angle, 3°, 5°, 8°, 11°, 14°, 17°, 20°, set by measuring height and length, with 5 runs per angle.",
   "dependentVariable": "Acceleration from two light gates, or from the gradient of a speed against time graph from a motion sensor. Sin θ is calculated from height divided by track length.",
   "controlledVariables": "Trolley mass fixed, with a check run with added mass. Same start position and the same distance between gates. Same track and wheels, cleaned each session. Angle checked before each release.",
   "physicsNeeded": "ma = mg sinθ − F_r, so a = g sinθ − F_r/m. Plot a (y) against sinθ (x). The gradient should be g and the negative intercept is F_r/m. Do it for a second mass to test whether F_r changes.",
   "slVsHl": "SL students can obtain g and comment on the intercept. Reaching the top band means quantifying the friction force and its uncertainty. HL students can go further by including the rotational inertia of the wheels, which lowers the gradient below g.",
   "whereMarksAreLost": "Research design: angle chosen with a protractor on a steep range only. Data analysis: forcing the line through the origin. Conclusion: failing to explain a gradient below 9.81 m/s². Evaluation: this topic is overdone, so identical evaluation points lose impact.",
   "dataNote": "Uses a track, trolley and light gates or a phone video, and the main uncertainty is the angle from height measurements at shallow slopes.",
   "verdict": "Common, so the version that works is the intercept one. The three variants about a golf ball, a block and friction coefficients are the same physics, and a friction coefficient from the intercept is a good twist."
  },
  {
   "id": "cantilever-length-and-end-deflection-of-a-metal-strip",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Cantilever length and end deflection of a metal strip",
   "researchQuestion": "How does the free length of a clamped steel strip (0.15 to 0.40 m, 6 lengths) affect its end deflection under a fixed 100 g load, and what Young's modulus follows?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 3,
   "independentVariable": "Free length L from 0.15 to 0.40 m in 0.05 m steps, 3 repeats each, on a strip clamped at a bench edge.",
   "dependentVariable": "End deflection measured with a rule against a fixed vertical scale or from a photograph, in mm. Young's modulus calculated from the gradient.",
   "controlledVariables": "Same strip, so width and thickness are fixed and measured with a micrometer. Same 100 g load hung at the end. Same clamp tightness. Deflection kept small so the response is elastic.",
   "physicsNeeded": "For a cantilever δ = 4FL³/(Ewt³). Plot δ against L³; the gradient is 4F/(Ewt³), so E = 4F/(gradient × wt³). Compare with the tabulated value for steel.",
   "slVsHl": "SL students can do the cubic linearisation and estimate E. The top band handles the thickness uncertainty, which enters cubed, and the clamp not being perfectly rigid.",
   "whereMarksAreLost": "Research design: taking a beam supported at both ends and guessing the formula. Data analysis: not linearising the cube or ignoring the thickness uncertainty. Evaluation: strip weight adding its own sag.",
   "dataNote": "Needs a metal strip, clamp, micrometer and a way to read small deflection; thickness is the main uncertainty.",
   "verdict": "A good choice as the cubic law gives a strong signal. Use several materials (steel, brass, aluminium) for a personal angle."
  },
  {
   "id": "drag-on-falling-paper-cones-with-changing-area",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Drag on falling paper cones with changing area",
   "researchQuestion": "How does the frontal area A of paper cones cut from circles of radius 6 cm to 12 cm, with the same mass, affect terminal speed, and is v proportional to 1/√A?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 3,
   "independentVariable": "Cone base area from 20 cm² to 100 cm², 6 to 8 values, made by cutting different sectors or sizes, with 5 drops each.",
   "dependentVariable": "Terminal speed from a video of the fall against a metre rule, using the linear part of the position time graph. Calculated quantity is 1/√A.",
   "controlledVariables": "Mass kept the same by adding small paper or clay ballast, checked on a 0.01 g balance. Same paper. Same drop height of about 2.5 m. Air movement kept low. Cone shape kept consistent.",
   "physicsNeeded": "mg = ½ρC_D A v², so v = √(2mg/(ρC_D)) × A^(−1/2). Plot v (y) against 1/√A (x) to get a straight line through the origin with gradient √(2mg/(ρC_D)).",
   "slVsHl": "SL students can show that terminal speed falls as area rises and test the line. Top band means holding mass fixed properly and discussing C_D. HL students can test alternative drag models with a log-log fit.",
   "whereMarksAreLost": "Research design: mass changes when area changes, so two variables move at once. Data analysis: no uncertainty for area. Conclusion: not linking the gradient to C_D. Evaluation: drift and tumbling not analysed.",
   "dataNote": "Needs a phone camera, a balance and paper, and the hardest thing is keeping mass constant across different cone sizes.",
   "verdict": "Worth doing if mass is truly controlled, which most students miss. Stay with paper cones, not footballs, because balls of different sizes differ in mass and surface."
  },
  {
   "id": "ball-spin-and-sideways-drift-in-flight",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Ball spin and sideways drift in flight",
   "researchQuestion": "How does the spin rate of a table tennis ball (about 5 to 30 rev/s, 6 values) affect its sideways deflection over a 1.5 m horizontal launch?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Spin rate, set with a spinning launcher of two wheels at different speeds, found from slow motion video at 240 fps. 6 settings, 5 launches each.",
   "dependentVariable": "Sideways or vertical deflection at a fixed distance, measured from video against a scale grid. Spin rate from counting marker rotations per second.",
   "controlledVariables": "Same ball and same launch speed, checked from video tracking. Room closed to stop draughts. Same launch height and angle. Same distance to the target grid.",
   "physicsNeeded": "The Magnus force is proportional to spin and speed, so deflection d = ½at² with a = F/m. Plot deflection against spin rate; expect an approximate straight line at low spin.",
   "slVsHl": "SL students report deflection against spin and comment on the trend. Top band work estimates the lift coefficient and compares with a model, treating the change in launch speed as the wheels change.",
   "whereMarksAreLost": "Research design: a basketball dropped from height has almost no horizontal velocity, so the Magnus force is negligible. Data analysis: no uncertainty in spin from video. Evaluation: draughts and inconsistent launch speed.",
   "dataNote": "Needs a launcher and slow motion video; hard to hold launch speed constant while varying spin.",
   "verdict": "Interesting but hard to do cleanly. Do not follow the drop version, as it barely shows Magnus. Only choose it if you can build a repeatable launcher."
  },
  {
   "id": "friction-of-a-wooden-block-as-load-increases",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Friction of a wooden block as load increases",
   "researchQuestion": "How does the normal force on a wooden block (load from 0.2 to 1.2 N in 6 steps by adding masses) affect the maximum static and the kinetic friction on a felt surface?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Normal force, 6 to 8 values from added masses, each run at least 5 times.",
   "dependentVariable": "Force from a force sensor pulling the block steadily by string. Peak of the trace gives maximum static friction and the plateau gives kinetic friction.",
   "controlledVariables": "Same surface pair and the same contact area. Pulling speed kept slow and steady by a motor or by careful hand pulling. Same surface cleaned and reset between runs. Laboratory temperature and humidity noted.",
   "physicsNeeded": "F ≤ μN. Plot both friction values against N; the gradients give μs and μk, and a non-zero intercept shows the model failing. Static should be above kinetic.",
   "slVsHl": "SL work compares both gradients and considers the intercept. Top band adds a second material or contact area and asks when friction is not proportional to N.",
   "whereMarksAreLost": "Research design: pulling by hand so speed varies. Data analysis: forcing the line through the origin. Evaluation: surface wear between runs, which changes μ.",
   "dataNote": "A force sensor makes it good; a newton meter works but reading the peak is difficult, and surface wear is the main uncertainty.",
   "verdict": "Simple and overdone, so it needs both static and kinetic values and a proper check of the intercept. Try an unusual surface pair for a personal angle."
  },
  {
   "id": "terminal-speed-of-stacked-coffee-filters-against-weight",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Terminal speed of stacked coffee filters against weight",
   "researchQuestion": "How does the number of nested coffee filters, from 1 to 8, affect the terminal speed reached when dropped from 2.5 m, and does drag follow v² proportional to weight?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Number of identical nested coffee filters, 1 to 8, so mass from about 1 g to 8 g, with 5 drops for each.",
   "dependentVariable": "Terminal speed from the slope of the position against time graph in phone video with a metre rule in view, using the last 1 m of fall. Calculated quantity is v², and weight W = mg from a balance.",
   "controlledVariables": "Same brand and shape of filter, nested the same way and held level. Same drop height and start. Windows and fans off, with the drop in a stairwell or a hall. Same camera position and frame rate.",
   "physicsNeeded": "At terminal speed, mg = ½ρC_D A v², so v² = 2mg/(ρC_D A). Plot v² (y) against m (x). The gradient is 2g/(ρC_D A), giving C_D. A power law fit tests whether the exponent is 2.",
   "slVsHl": "SL students can show the linear v² against m trend and estimate C_D. To reach top band, discuss why the shape may change and whether the flow is quadratic drag. HL students can add the Reynolds number and a comparison of models.",
   "whereMarksAreLost": "Research design: dropping over too short a height so the filters never reach terminal speed. Data analysis: reading v from two points, not a fit. Conclusion: claiming a linear v against m trend without testing. Evaluation: not commenting on filters flipping or tumbling.",
   "dataNote": "A phone at 60 to 240 fps and a rule are enough, and the largest uncertainty is a filter that wobbles and drifts out of frame.",
   "verdict": "Popular and easy to run, so it needs the v² test to be worthwhile. Skip the toy parachute, balloon and marble variants as separate ideas. The marble in water is a different regime and needs a Stokes' law discussion."
  },
  {
   "id": "whirled-bung-force-on-the-string-against-angular-speed",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Whirled bung: force on the string against angular speed",
   "researchQuestion": "How does the angular speed of a 50 g rubber bung on a 0.50 m radius (ω from about 4 to 14 rad/s, 6 values) affect the tension in its string, measured with a force sensor?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Angular speed ω, set by timing 20 revolutions with a stopwatch or a phone video; 6 values with 3 repeats.",
   "dependentVariable": "Tension in the string from a force sensor mounted on the rotating arm or a turntable rig, in N. Compare with mω²r calculated from the timings.",
   "controlledVariables": "Mass of the bung fixed and weighed. Radius fixed by a marker on the string and checked from video. Circle kept horizontal by using a turntable or rigid arm. Same sensor zeroing before each run.",
   "physicsNeeded": "F = mω²r. Plot F against ω²; the gradient should equal mr. Compare it with the value from the measured mass and radius.",
   "slVsHl": "SL students do the F against ω² graph and check the gradient. Top band work handles the string angle when the bung is swung by hand and treats the fixed uncertainty in period timing.",
   "whereMarksAreLost": "Research design: a hand-whirled bung does not stay horizontal, so the tension is not the centripetal force. Data analysis: plotting F against ω and calling it a curve without linearising. Evaluation: radius changing during the swing.",
   "dataNote": "A rotating rig with a force sensor is best; hand whirling is cheap but the angle and speed are hard to hold constant.",
   "verdict": "A sound choice if you have a proper rig. The twist is repeating with a different radius to test the mass times radius gradient."
  },
  {
   "id": "acceleration-of-a-trolley-against-net-force-and-drag",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Acceleration of a trolley against net force and drag",
   "researchQuestion": "How does the acceleration of a 0.50 kg dynamics trolley on a level track vary with driving force from 0.10 N to 0.60 N, with and without a card sail attached?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Driving force from hanging masses (10 g to 60 g in 10 g steps, weight transferred from trolley to hanger so total mass is constant), with two conditions: no sail and a fixed 10 cm by 10 cm card sail.",
   "dependentVariable": "Acceleration from a motion sensor or light gate velocity readings, or from video analysis in Tracker (m s⁻²), with three runs per value.",
   "controlledVariables": "Total system mass kept constant by moving masses between hanger and trolley. Track levelled or friction compensated and checked. Sail area and orientation fixed. Release point and distance the same.",
   "physicsNeeded": "F = ma for the whole system. Plot a against F: gradient is 1/m. With a sail, the graph curves or has a lower gradient as drag grows with speed, which lets you estimate a drag coefficient from the deficit.",
   "slVsHl": "SL: a against F for the no-sail case and comparison of the gradient with 1/m. Top band: model drag as kv² and extract k, discuss friction as an intercept, and check that acceleration is uniform over the measured section.",
   "whereMarksAreLost": "Research design: the original wording of comparing 'types of force' is not measurable; also changing mass and force together. Data analysis: forcing the line through the origin. Conclusion: no comparison of the gradient with 1/m. Evaluation: ignoring pulley friction and string mass.",
   "dataNote": "Needs a dynamics track, trolley and either light gates or video; the main uncertainty is friction and short timing distances.",
   "verdict": "Solid and doable, but choose the constant-total-mass method and the drag extension or it is a textbook lab. Personalise it with a sail shape of your own design."
  },
  {
   "id": "apparent-weight-loss-in-liquids-and-archimedes-principle",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Apparent weight loss in liquids and Archimedes' principle",
   "researchQuestion": "How does the upthrust on a fully submerged 100 g brass cylinder change with liquid density from 800 kg m⁻³ to 1250 kg m⁻³ using five liquids or salt solutions?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Liquid density: vegetable oil, ethanol solution, tap water, and three salt solutions at about 1050, 1150 and 1250 kg m⁻³, each density measured with a measuring cylinder and balance.",
   "dependentVariable": "Upthrust from the drop in reading on a newton meter or a top-pan balance (N), taken as weight in air minus apparent weight in liquid, with three repeats.",
   "controlledVariables": "Object: same cylinder, fully submerged and not touching the container. Depth: fixed with a marked string length. Temperature: same room, measured. Air bubbles: removed by tapping before reading.",
   "physicsNeeded": "Upthrust = ρVg. Plot upthrust against liquid density: a straight line through the origin with gradient Vg, which gives the object's volume for comparison with the measured value.",
   "slVsHl": "SL: line through the origin and volume from the gradient. Top band: use a balance-based method to reduce reading error, discuss the effect of surface tension on the thread, and test partial submersion and depth as controls.",
   "whereMarksAreLost": "Research design: viscous syrup makes readings hard and mixes in a different variable; use densities you can measure. Data analysis: not measuring density directly. Conclusion: no comparison of gradient with Vg. Evaluation: ignoring bubbles and thread effects.",
   "dataNote": "Newton meter or top-pan balance, measuring cylinder and liquids; the main uncertainty is the coarse resolution of a newton meter, so a balance is preferred.",
   "verdict": "Simple but perfectly reasonable if density is measured rather than assumed. Make it personal with a real-world twist such as saltwater versus fresh water flotation, like the Dead Sea."
  },
  {
   "id": "ball-size-and-momentum-change-from-a-fixed-energy-launch",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Ball size and momentum change from a fixed-energy launch",
   "researchQuestion": "How does the radius of a ball, from 2 cm to 11 cm across at least five ball types, affect the impulse it receives from a spring-loaded striker released from the same compression?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Ball radius, five to six balls (for example ping pong, squash, tennis, softball, size 3 football and size 5 football), measured with vernier callipers.",
   "dependentVariable": "Launch speed from the distance between two light gates or 240 fps video over 0.5 m; impulse calculated as J = mv, with mass on a 0.1 g balance.",
   "controlledVariables": "Striker energy, using the same spring compression each release. Ball position on the striker, marked on the surface. Surface friction, using a smooth level track. Ball inflation, checked with a pressure gauge for the air-filled ones.",
   "physicsNeeded": "Impulse equals change in momentum, J = Δp = mv. Balls differ in mass and elasticity as well as radius, so plot J against radius, then J against mass to see which is the real driver. A person kicking cannot give a fixed force, hence the spring striker.",
   "slVsHl": "SL: plot J against r and comment on scatter and other differences between balls. Top band: separate the effects of mass and stiffness with J against m, and test against an energy conservation model with restitution.",
   "whereMarksAreLost": "Research design: radius cannot be varied on its own since mass and material change too; kicking by foot is not repeatable. Conclusion: claiming radius is the cause. Data analysis: no propagation of uncertainty in speed.",
   "dataNote": "Requires a spring launcher, light gates or video, and a balance; the launch repeatability is about ±3%.",
   "verdict": "Only worth choosing if you accept that radius is confounded with mass. The twist: make the question about mass and radius separately and pick the better plot."
  },
  {
   "id": "bending-of-beams-made-of-different-materials",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Bending of beams made of different materials",
   "researchQuestion": "How does the Young modulus, found from the sag of a 50 cm strip clamped at one end, differ between pine, aluminium, steel and acrylic strips of equal width and thickness under loads of 50 g to 300 g?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Load hung at the free end, 6 values from 50 g to 300 g in 50 g steps, for each of 4 materials, with 3 repeats per load.",
   "dependentVariable": "Deflection of the free end, read with a metre rule against a fixed mark or from a photo. Young modulus is calculated from the gradient of load against deflection.",
   "controlledVariables": "Strip dimensions: measured with a micrometer and vernier caliper and kept the same. Clamped length: marked and fixed at 40 cm. Load position: hung at the same point each time. Temperature and time under load: read after 30 seconds each.",
   "physicsNeeded": "For a cantilever, deflection δ = FL³/(3EI) with I = wt³/12. Plot δ against F, gradient L³/(3EI), so E = L³/(3 × gradient × I). Compare with tabulated E. Stay in the elastic range by checking that the strip returns to zero.",
   "slVsHl": "SL students can use the simpler tensile stress and strain idea with a wire and keep the beam as a comparison of stiffness. Top band work compares E with data tables, quantifies the uncertainty in the thickness which enters as t³, and checks the elastic limit.",
   "whereMarksAreLost": "Research design: several dimensions change between materials, so the comparison is not fair. Data analysis: thickness uncertainty ignored although cubed. Conclusion: claiming strength when only stiffness in the elastic range was measured. Evaluation: the clamp slips.",
   "dataNote": "Needs strips, a G-clamp, masses and a ruler, and the main uncertainty is the thickness measurement and clamp movement.",
   "verdict": "Good if you restrict it to stiffness and avoid breaking things. Strength to failure is messy and not repeatable, so keep it to elastic behaviour."
  },
  {
   "id": "bending-stiffness-of-a-plastic-ruler-at-different-temperatures",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Bending stiffness of a plastic ruler at different temperatures",
   "researchQuestion": "How does the temperature of a plastic ruler, from 5 °C to 60 °C, affect its Young's modulus as found from the sag under a fixed load?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Temperature of the ruler: about 5, 15, 25, 35, 45, 60 °C (6 values), set using ice water, room air and a warm water bath, with the ruler dried and measured in the same setup within a short time.",
   "dependentVariable": "Deflection at the free end of a cantilever ruler under a fixed mass, read with a set square or from photographs against a scale. Young's modulus E = 4FL³/(w t³ δ) from the deflection, with width w and thickness t measured with a micrometer.",
   "controlledVariables": "Same ruler, clamped with the same overhang length. Same load, kept small so that deflection stays in the elastic range. Ruler thickness measured at several places. Time from bath to reading kept the same, as the ruler cools quickly.",
   "physicsNeeded": "For a cantilever, δ = 4FL³/(E w t³), so E follows from measured deflection. Plot E against temperature, or plot 1/δ against temperature, since 1/δ is proportional to E. Discuss the change near the glass transition of the polymer.",
   "slVsHl": "SL: measure deflection at a range of temperatures and show the trend in E. Top band: check the linearity of force against deflection at one temperature first, and estimate the temperature of the ruler at measurement. The beam formula is not in the syllabus so it must be derived or sourced carefully.",
   "whereMarksAreLost": "Research design: the ruler cools or warms between the bath and the reading, so the recorded temperature is wrong. Data analysis: applying the formula without a consistent way of measuring thickness. Conclusion: extending a trend beyond the tested range. Evaluation: ignoring creep of the plastic under a constant load.",
   "dataNote": "Needs a plastic ruler, clamp, masses, a water bath and a thermometer; the main uncertainty is temperature loss and the small deflection.",
   "verdict": "A creative idea, but strictly it fits mechanics of materials, which the syllabus only touches lightly. Manageable if you derive the beam formula and keep the temperature under tight control."
  },
  {
   "id": "blood-pressure-reading-against-arm-height-above-the-heart",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Blood pressure reading against arm height above the heart",
   "researchQuestion": "How does the systolic pressure reading from a digital cuff change when the cuffed wrist is held at heights from 40 cm below to 40 cm above heart level, in 10 cm steps?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Vertical height of the cuff relative to the heart, in 10 cm steps from -40 to +40 cm (9 values), measured with a metre rule against a fixed mark, with 3 readings each.",
   "dependentVariable": "Systolic pressure reading in mmHg from a wrist digital monitor, converted to pascals with 1 mmHg = 133 Pa.",
   "controlledVariables": "Participant: one volunteer, seated. Rest: 3 minutes between readings. Time of day: same hour, no caffeine. Cuff position on the wrist and arm support: same, with the arm relaxed.",
   "physicsNeeded": "Hydrostatic pressure gives Δp = ρgΔh, with blood density about 1060 kg m⁻³. Plot pressure (y) against height (x); predicted gradient is ρg ≈ 7.8 mmHg per 10 cm ≈ 0.78 mmHg per cm. Compare the measured gradient with this.",
   "slVsHl": "SL students plot pressure against height and compare with ρg. Top band work discusses why the effect is smaller in living arteries and veins (valves, vessel tone), and treats the light-exercise data as a separate question.",
   "whereMarksAreLost": "Research design: consumer monitors have poor resolution and natural variation is often bigger than the effect. Data analysis: ignoring the spread between repeats. Evaluation: not discussing the ethics of medical measurements.",
   "dataNote": "Needs a wrist blood pressure monitor and a metre rule; readings vary by several mmHg between repeats, which may hide the trend.",
   "verdict": "Risky but interesting. The result can be noisy, and the human participant needs approval, so I would only pick it with 5+ repeats. Comparing against ρgΔh gives a clear test."
  },
  {
   "id": "buoyant-force-on-submerged-cylinders-of-different-volume",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Buoyant force on submerged cylinders of different volume",
   "researchQuestion": "How does the volume of a fully submerged aluminium cylinder (5 to 40 cm³, 8 values) affect the apparent loss of weight measured on a newton meter in water?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Volume of the submerged object, 5 to 40 cm³ in 8 steps, made by using cylinders of equal material and different lengths, or by stacking identical metal discs. Three repeats per volume.",
   "dependentVariable": "Weight in air and weight when fully submerged, read with a 0 to 5 N newton meter or a force sensor. Buoyant force is the difference. Compare with ρgV calculated from the measured volume.",
   "controlledVariables": "Fluid density: same tap water, temperature recorded. Full submersion with no contact with the beaker walls or base. Same suspension thread. Same reading procedure, eye level with the pointer, or a zeroed force sensor.",
   "physicsNeeded": "Archimedes: F_b = ρ_fluid V g. Plot F_b (y) against V (x). It should be a straight line through the origin, and the gradient equals ρg, which can be compared with 9.81 × 1000 N m⁻³. Volume is best found from a measured displacement in a measuring cylinder as a cross-check.",
   "slVsHl": "An SL student can get a good line, a gradient and a percentage difference from ρg. Top band work checks the intercept, treats the thread and pointer uncertainties and repeats with a second liquid such as brine to show the gradient changes with density. Nothing here needs HL content.",
   "whereMarksAreLost": "Research design: small volume range so force differences are lost in the newton meter resolution. Data analysis: uncertainty in volume ignored. Conclusion: claiming Archimedes is confirmed without comparing the gradient to the accepted value. Evaluation: not discussing that the two supplied entries are the same investigation, and that force sensor resolution limits the small volumes.",
   "dataNote": "A newton meter, measuring cylinder and metal cylinders are enough, but a 0.05 N resolution makes small volumes poor, so a force sensor helps.",
   "verdict": "Simple and safe, but it is a textbook check and will look thin unless you add a second fluid or a good uncertainty analysis. Twist: test the gradient against a salt solution of known density that you make yourself."
  },
  {
   "id": "cart-collisions-mass-ratio-restitution-and-momentum",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Cart collisions: mass ratio, restitution and momentum",
   "researchQuestion": "How does the mass ratio of a moving cart to a stationary cart (from 0.25 to 4.0, 6 values) affect the coefficient of restitution in a head-on collision on a level track?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Mass of the target cart relative to the moving cart, from 0.25 to 4.0, by adding 0.25 to 1.0 kg masses. Each ratio repeated 5 times.",
   "dependentVariable": "Speeds before and after impact from two light gates or from Tracker on a video. Coefficient of restitution e = (relative speed after)/(relative speed before). Total momentum before and after is also calculated.",
   "controlledVariables": "Incoming speed: same push from a spring plunger. Track level: checked with a spirit level. Contact surfaces: same bumpers throughout. Mass of moving cart: fixed at 0.500 kg.",
   "physicsNeeded": "Momentum is conserved: m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂. Restitution is e = (v₂ − v₁)/(u₁ − u₂). Plot e against mass ratio and see whether it is constant. Plot total momentum after against total momentum before, where the gradient should be 1. Kinetic energy loss can also be found.",
   "slVsHl": "SL students can check momentum and compute e. Better work explains why e might depend on mass ratio, if it does, through cart deformation and contact time. HL students may work in the centre of mass frame to analyse the energy loss.",
   "whereMarksAreLost": "Research design: two different questions (e and momentum) with no clear focus. Data analysis: light gates give speeds for the flag length only and the impact speed is ignored. Evaluation: ignores friction on wheels that makes the momentum before and after different.",
   "dataNote": "Needs a dynamics track, two light gates or video tracking; the main uncertainty is friction and speed measurement near the impact.",
   "verdict": "Choose it if you commit to one clear question, probably whether e depends on mass ratio, and show momentum as a check. The result that e stays constant is still a valid finding."
  },
  {
   "id": "comparing-density-methods-for-metals-and-plastics",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Comparing density methods for metals and plastics",
   "researchQuestion": "How consistent are densities of six solid samples (aluminium, brass, steel, copper, acrylic, PVC) found by direct measurement of volume and by displacement in water, compared with data book values?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Material of the sample: 6 different solids, each with 3 samples of different sizes to test that density does not depend on size, with each method repeated 3 times.",
   "dependentVariable": "Mass from a balance to 0.01 g, volume from callipers (regular shapes) and from a measuring cylinder or a eureka can (displacement); density is mass over volume for each method, with percentage difference to the data book.",
   "controlledVariables": "Water temperature: recorded and kept near room temperature. Air bubbles: samples tapped to remove them before reading. Reading position: at eye level of the meniscus. Sample surface: dried before weighing.",
   "physicsNeeded": "rho = m / V. Plot mass against volume for each material; the gradient is the density and the points should lie on a line through the origin. Alternatively compare the buoyancy method using apparent weight in water, W_app = W minus rho_w V g.",
   "slVsHl": "SL students compare the two methods with uncertainties and a percentage difference. Higher marks come from a buoyancy-based third method and a clear argument about which method has the least uncertainty for small samples.",
   "whereMarksAreLost": "Research design: there is no real question beyond looking up densities. Data analysis: combining uncertainty in volume from three lengths incorrectly. Conclusion: not saying which method is better or by how much.",
   "dataNote": "Balance, vernier callipers, measuring cylinder and samples; the main uncertainty is the small volume for displacement, giving a large percentage error.",
   "verdict": "Too basic as stated, with little physics beyond a definition. Frame it as a method comparison using apparent weight in water, which links to A.2 buoyancy, or skip it."
  },
  {
   "id": "cushion-thickness-and-peak-force-in-a-crash",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Cushion thickness and peak force in a crash",
   "researchQuestion": "How does the thickness of a foam cushion (0.5 to 3.0 cm in 6 steps) affect the peak force on a 0.500 kg trolley that hits it at 1.0 m/s?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Foam thickness from 0.5 to 3.0 cm, 6 values, made from stacks of equal foam sheets. Each value tested 5 times.",
   "dependentVariable": "Force from a force sensor with a data logger at 1000 Hz or more. Peak force is read from the graph; impulse is the area under the graph, compared with mΔv from the gate speeds.",
   "controlledVariables": "Impact speed: same release height on a ramp, checked with a light gate. Trolley mass: fixed at 0.500 kg. Foam type and area: same material cut to the same size. Rebound: check that the trolley does not bounce much.",
   "physicsNeeded": "Impulse FΔt = Δp, so for the same Δp a longer collision time gives a lower average force. Plot peak force against 1/thickness or against collision time. Compare the impulse area with mΔv to test the method.",
   "slVsHl": "SL students can show the trend and compare impulse with change of momentum. Higher marks come from a model of the foam as a spring giving a time of contact and force. HL students can consider the foam as a damped spring.",
   "whereMarksAreLost": "Research design: impact speed is not the same between trials. Data analysis: sampling too slow so the peak is missed. Evaluation: the foam is compressed by earlier trials and changes.",
   "dataNote": "A force sensor with a fast logger is essential; the main uncertainty is sampling rate and foam wear over repeats.",
   "verdict": "A practical idea with a real world link and a clear check against theory. Worth choosing if your school has a fast force sensor."
  },
  {
   "id": "draining-time-of-a-bottle-at-different-water-heights",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Draining time of a bottle at different water heights",
   "researchQuestion": "How does the starting water height h (6.0, 8.0, 10.0, 12.0, 14.0, 16.0 cm ± 0.1 cm) above a 4 mm side hole in a plastic bottle affect the initial volumetric flow rate, in cm³ s⁻¹?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Height of water above the hole, 6 values from 6.0 to 16.0 cm, each run 3 times, using a ruler taped to the bottle.",
   "dependentVariable": "Volume leaving in a fixed interval, measured with a measuring cylinder under the hole and a stopwatch (or phone video), giving flow rate Q = V/t. Also the range of the jet can be measured to get exit speed.",
   "controlledVariables": "Hole diameter: drilled once and checked with a calliper. Water temperature: measured with a thermometer before each run. Bottle shape: same cylindrical bottle, so the surface level drops slowly. Time interval: short (e.g. 5 s) so h barely changes.",
   "physicsNeeded": "Torricelli's result v = √(2gh) follows from Bernoulli, and Q = Av. Plot Q² against h: a straight line through the origin with gradient 2gA². Compare the gradient with the measured hole area. Fluid dynamics is not formally in the syllabus, so energy conservation for a small parcel of water can be used as the argument.",
   "slVsHl": "SL: plot Q against h, find the trend, and test the square root shape. Top band, both levels: linearise, compare the gradient to 2gA², and discuss a discharge coefficient below 1 and the effect of viscosity and surface tension for a small hole.",
   "whereMarksAreLost": "Research design: letting h fall during a long collection so it is not a single height. Data analysis: uncertainty in timing a short interval is large and often ignored. Conclusion: claiming 'proportional' when the data fit √h. Evaluation: not commenting on why the measured gradient is below the theoretical value.",
   "dataNote": "A bottle, measuring cylinder, stopwatch and ruler are enough, but the main uncertainty is timing short collections and the falling water level.",
   "verdict": "Cheap, clear and testable against theory, which makes it a good choice if you do the Q² linearisation and the discharge coefficient. Make it personal by using a real bottle or a tank you have at home and comparing hole sizes."
  },
  {
   "id": "grease-temperature-and-impact-crater-depth",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Grease temperature and impact crater depth",
   "researchQuestion": "How does the temperature of a tub of petroleum jelly, varied from 10 °C to 50 °C in steps of 10 °C, affect the depth of the crater made by a steel ball dropped from 0.50 m?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Temperature of the grease or petroleum jelly, 10, 20, 30, 40, 50 °C (5 values), set in a water bath, with 5 drops at each temperature.",
   "dependentVariable": "Crater depth in mm, measured with a depth gauge or a needle and ruler after each drop. Energy lost to the grease is then calculated from the ball's kinetic energy at impact, or the stopping force is estimated from depth.",
   "controlledVariables": "Drop height fixed with a clamped release and metre rule. Same ball mass and diameter every time. Grease surface smoothed flat before each drop, and a fresh spot used each time. Temperature checked with a thermometer just before and after each drop, since grease cools quickly.",
   "physicsNeeded": "Energy conservation, mgh = F·d for an average stopping force, and the link between temperature and viscosity. Plot ln(depth) against 1/T, or depth against temperature, and comment on whether the trend is exponential like viscosity. Gradient links to how strongly resistance changes with temperature.",
   "slVsHl": "SL students can plot depth against temperature and estimate average stopping force from work done. Top band work tests a linearised model of viscosity against temperature, compares with a second drop height, and explains why crater depth is not simply proportional to viscosity.",
   "whereMarksAreLost": "Research design: temperature drifting during the trial, and no justification of the drop height. Data analysis: ignoring uncertainty in reading depth from a soft, ragged crater. Conclusion: claiming a viscosity value when only depth was measured. Evaluation: not discussing that grease is non-Newtonian and deforms rather than flows.",
   "dataNote": "Needs a water bath, thermometer and a way to measure depth in soft material; the main uncertainty is a poorly defined crater bottom and temperature loss during the drop.",
   "verdict": "Worth choosing if you want something hands on and slightly messy. Make it personal by using a grease or food product you can justify, and be honest that you measure resistance to penetration, not true viscosity."
  },
  {
   "id": "inflation-pressure-and-rolling-tyre-drag-on-a-slope",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Inflation pressure and rolling tyre drag on a slope",
   "researchQuestion": "How does the inflation pressure of a bicycle tyre, from 100 kPa to 400 kPa in 5 steps, affect the coefficient of friction measured by the tilt angle at which a loaded wheel just starts to slide on a wooden board?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Tyre gauge pressure, 100, 150, 200, 300, 400 kPa (5 values), set with a pump and gauge, 5 repeats each.",
   "dependentVariable": "Force to pull the tyre at steady speed with a newton meter or force sensor, or the angle at which a locked wheel slides on a tilting board. μ = F/N, or μ = tan θ.",
   "controlledVariables": "Load on the tyre (fixed added mass). Surface (same board, cleaned). Pulling speed. Tyre temperature and wear, using one tyre.",
   "physicsNeeded": "F = μN, with N = mg on a level surface, or μ = tan θ on a slope at the point of sliding. Plot μ against pressure, or against 1/pressure to test whether contact area is involved.",
   "slVsHl": "SL: measure μ for each pressure and comment on the trend. Deeper: relate contact area to pressure using A = N/P and discuss why classical friction predicts no dependence.",
   "whereMarksAreLost": "Research design: pressure loss during tests that is not checked. Data analysis: mixing rolling and sliding friction. Conclusion: claiming that contact area matters without measuring it.",
   "dataNote": "Needs a bicycle pump with gauge and a force sensor; the pressure leak and locked wheel technique are the main uncertainty.",
   "verdict": "Good if you measure the contact patch with ink, so that the physics is tested and not assumed. Lock the wheel so that you really measure sliding."
  },
  {
   "id": "lift-on-a-flat-plate-against-fan-speed",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Lift on a flat plate against fan speed",
   "researchQuestion": "How does air speed, varied from 2 to 10 m/s in six steps, affect the lift force on a flat card wing set at a fixed 15° angle of attack in a small wind tunnel?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Air speed through the working section, 2, 4, 6, 8, 10 and 12 m/s, set by fan voltage and checked with a handheld anemometer. Three repeats at each speed.",
   "dependentVariable": "Lift force, measured with a top-pan balance or a 0 to 1 N force sensor holding the wing on a low-friction pivot arm. Air speed from the anemometer. Lift coefficient calculated from L = 0.5 ρ v² A C.",
   "controlledVariables": "Angle of attack: fixed with a protractor jig. Wing area and shape: the same card wing throughout. Air density: room temperature and pressure recorded. Blockage and turbulence: wing kept in the middle of the section, same distance from the fan and flow straightener.",
   "physicsNeeded": "Lift scales as v² for a fixed wing, from momentum change of deflected air. Plot L against v². A straight line through the origin has gradient 0.5 ρ A C, which gives C. Compare C with published values for flat plates.",
   "slVsHl": "SL: measure L against v, test the v² relationship and find C. Top band: check the Reynolds number range, explain deviation at high speed by stall or vibration, and compare with a momentum-flux estimate. HL adds nothing syllabus-wise but the fluid ideas give depth.",
   "whereMarksAreLost": "Research design: air speed that is not uniform across the wing and no anemometer calibration. Data analysis: plotting L against v and calling it linear without testing v². Evaluation: ignoring wall effects and fan pulsing, which dominate the error.",
   "dataNote": "Needs a tunnel or a box fan with a straightening tube, an anemometer and a sensitive force measurement; forces are only a few tenths of a newton and the flow fluctuates.",
   "verdict": "Worth it only if your school has a tunnel or you can build a decent one. The twist is to make your own wing and justify how you measured a very small force."
  },
  {
   "id": "lift-on-a-model-wing-as-its-tilt-changes",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Lift on a model wing as its tilt changes",
   "researchQuestion": "How does the angle of attack of a cardboard or foam aerofoil, varied from 0° to 30° in 5° steps, affect the lift force measured in a fan-driven airflow at a fixed speed of about 5 m s⁻¹?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Angle of attack from 0° to 30° in 5° steps (7 values), each with 3 repeats.",
   "dependentVariable": "Lift measured as an apparent mass change on a top-pan balance or with a force sensor (±0.01 N). Lift coefficient can be calculated from the lift, air density, wing area and air speed.",
   "controlledVariables": "Air speed, checked with an anemometer at the wing position each run. Wing shape and area, by using one wing. Distance from fan, fixed with a marked stand. Room air movement, minimised by shielding.",
   "physicsNeeded": "Lift arises from momentum change of deflected air, L = ½ρv²AC_L. Plot lift against angle to show the linear region and the stall point, then plot C_L against angle for the linear part, where the gradient gives the lift slope.",
   "slVsHl": "SL students show the trend and locate the stall angle. Top band work compares C_L with published thin aerofoil data and justifies a physical model. Because this uses only A.2 ideas, depth comes from analysis, not HL content.",
   "whereMarksAreLost": "Research design: airflow from a fan is turbulent and non-uniform, and drag on the mount is not separated from lift. Data analysis: plotting raw force without normalising for speed. Conclusion: claiming stall angle with too few points near it. Evaluation: ignoring wall and edge effects and the sensor's drift.",
   "dataNote": "Needs a fan or small wind tunnel, an anemometer and a sensitive balance or force sensor. The main uncertainty is non-uniform airflow and fan speed drift.",
   "verdict": "Fun and visual but hard to get clean data. Worth it if you have some airflow control. Twist: test a 3D printed or cut-out wing based on a bird or paper plane you actually fly."
  },
  {
   "id": "load-position-along-a-cantilever-and-its-sag",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Load position along a cantilever and its sag",
   "researchQuestion": "How does the distance x of a 200 g load from the clamped end of a 60 cm steel or wooden ruler, from 10 cm to 50 cm in 5 steps, affect the vertical deflection at the free end?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Load position along the beam, 10, 20, 30, 40, 50 cm (5 values), measured with a metre rule, 3 repeats each.",
   "dependentVariable": "Deflection at the free end, read against a vertical rule or from a travelling microscope or a phone photo with a scale, in mm.",
   "controlledVariables": "Load mass (same hanger and slotted masses). Beam material and cross section (one ruler measured with calipers). Clamped length and clamp tightness. Temperature, and avoiding loading beyond the elastic limit.",
   "physicsNeeded": "For a point load at x on a cantilever, deflection at the tip goes as δ = Fx²(3L − x)/(6EI). Plot δ against x²(3L − x); the gradient is F/(6EI), which gives Young modulus E.",
   "slVsHl": "SL: plot deflection against x and describe the non linear shape. Strong work applies the beam equation, finds E and compares it with a data book, though the equation itself is beyond the syllabus and must be supported by derivation or source.",
   "whereMarksAreLost": "Research design: loading past the elastic limit. Data analysis: an unlinearised plot with no fit. Evaluation: ignoring the sag from the weight of the beam itself.",
   "dataNote": "Needs a ruler, clamp, masses and a scale; the main uncertainty is reading the tip position.",
   "verdict": "A good way to test the model, but the equation is not on the syllabus so you must source and justify it. Compare E to a book value for a clear conclusion."
  },
  {
   "id": "mass-of-a-block-and-distance-it-travels-after-a-pendulum-hit",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Mass of a block and distance it travels after a pendulum hit",
   "researchQuestion": "How does the mass of a wooden block, from 100 g to 500 g in steps of 100 g, affect the distance it slides along a bench after being struck by a pendulum hammer released from a fixed height?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Block mass: 100, 200, 300, 400 and 500 g, using stacked identical blocks or added masses, 5 repeats each.",
   "dependentVariable": "Slide distance measured with a metre rule (±1 mm), and speed of the block just after impact from 240 fps video; momentum transferred calculated as mv.",
   "controlledVariables": "Hammer mass and release height, fixed with a clamp and a stop. Contact surface, cleaned and using the same face. Point of impact on the block, marked with tape. Bench surface, the same track each time.",
   "physicsNeeded": "For a fixed impulse J, v = J/m, and the block then decelerates through friction so d = v²/(2μg) = J²/(2μg m²). Plot d against 1/m² and expect a straight line. Friction depends on m as well, which cancels in the expression, so the model is clean only if μ stays constant.",
   "slVsHl": "SL: plot d against 1/m² and discuss the fit. Top band: check that the impulse itself stays constant by measuring hammer speed after the collision, and treat the collision as partly elastic.",
   "whereMarksAreLost": "Research design: 'constant external force' cannot be created; a pendulum gives constant energy, not constant force. Data analysis: an unlinearised d against m plot that hides the model. Evaluation: not seeing that the hammer rebounds differently with each mass.",
   "dataNote": "Pendulum hammer, blocks and a rule; the main uncertainty is the collision repeatability, roughly ±5% in distance.",
   "verdict": "A good idea if you define the launch as a fixed pendulum release. The twist: use d against 1/m² so the physics decides the graph, not the other way round."
  },
  {
   "id": "maximum-load-of-a-model-boat-in-salt-water-of-different-concentration",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Maximum load of a model boat in salt water of different concentration",
   "researchQuestion": "How does the salt concentration of water (0 to 100 g/L in steps of 20 g/L) change the maximum mass a rectangular model boat can carry before it sinks to its marked waterline?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Salt concentration, 0, 20, 40, 60, 80, 100 g/L, made in a large tank with a balance and measuring cylinder. Three repeats per value.",
   "dependentVariable": "Mass added to the boat (weights or coins) to reach a fixed waterline mark, read on a balance. Fluid density from a hydrometer or from mass over volume of a sample. Upthrust is total mass times g.",
   "controlledVariables": "Boat shape and hull: same boat, waterline marked on the side. Water temperature: measured with a thermometer and kept about the same. Placement of load: centred, to avoid tilting. Water volume in tank: enough so the level does not affect the result.",
   "physicsNeeded": "Floating equilibrium: upthrust = weight, ρ V_sub g = (m_boat + m_load)g. With V_sub fixed by the waterline, m_load = ρV − m_boat. Plot m_load against ρ; the gradient is the submerged volume V and the intercept is −m_boat.",
   "slVsHl": "SL: plot m_load against density and check gradient with the calculated volume. Top band: uncertainty on density and waterline reading, and compare V from the gradient with V from the hull dimensions.",
   "whereMarksAreLost": "Research design: concentration not converted to density, so no linearisation is possible. Data analysis: no uncertainty on waterline. Conclusion: no link between gradient and volume. Evaluation: salt not fully dissolved or stratified in the tank.",
   "dataNote": "Needs a tank, salt, balance and a simple boat from a plastic box; the main uncertainty is the waterline reading and uneven mixing.",
   "verdict": "Easy and doable with cheap equipment, and gives a clean straight line. Twist: relate it to the Dead Sea or the Plimsoll line on real ships."
  },
  {
   "id": "momentum-conservation-in-trolley-collisions-using-light-gates",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Momentum conservation in trolley collisions using light gates",
   "researchQuestion": "How does the fractional change in total momentum in collisions between two dynamics trolleys vary with the initial speed of the moving trolley from 0.20 m/s to 1.00 m/s, on a level track?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Initial speed of the moving trolley, 5 to 6 values from 0.20 to 1.00 m/s, set by the release height on a small ramp or a spring plunger, with 3 repeats; a second series varies the mass of the target trolley from 0.5 to 2.0 kg.",
   "dependentVariable": "Velocities before and after collision from two light gates and cards, or video analysis at 120 frames per second; total momentum before and after, and the percentage change.",
   "controlledVariables": "Track level: checked with a spirit level and by a trolley that does not accelerate. Friction: same track and wheels, with compensation by a small tilt. Collision type: Velcro or magnetic ends, stayed the same. Masses: measured on a balance to 1 g.",
   "physicsNeeded": "Conservation of momentum, p = mv, total p before equals total p after for an isolated system. Plot total momentum after against total momentum before; the gradient should be 1, and kinetic energy checks distinguish elastic from inelastic collisions.",
   "slVsHl": "SL students compute momentum before and after with uncertainties and test a gradient of 1. Extra depth: measure kinetic energy lost and link it to collision type, and quantify the loss from friction using a coasting trolley.",
   "whereMarksAreLost": "Research design: two independent variables changed together, and no control over friction. Data analysis: ignoring uncertainties in card length and gate timing. Evaluation: not explaining a momentum shortfall by friction, or claiming conservation without a stated tolerance.",
   "dataNote": "Trolleys, track, two light gates and a data logger, or a phone camera for video analysis; the main uncertainty is friction and card-length timing error.",
   "verdict": "Well suited to a school lab and easy to get clean data, but commonly done. Make it your own by quantifying the losses and comparing elastic with inelastic ends."
  },
  {
   "id": "number-of-rotor-blades-against-thrust-at-fixed-speed",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Number of rotor blades against thrust at fixed speed",
   "researchQuestion": "How does the number of identical blades, from 2 to 6, on a motor-driven rotor affect the thrust measured with a top-pan balance at 1500 rpm?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Number of blades: 1, 2, 3, 4, 5 and 6 on a hub with equally spaced slots, 3 repeats each.",
   "dependentVariable": "Apparent mass loss on a 0.01 g balance (g), converted to thrust in N; rpm found by video frame counting.",
   "controlledVariables": "Rotor speed, adjusted with the supply voltage until the video count gives 1500 rpm. Blade size, pitch and material, all from one template. Hub height above the balance, clamp fixed. Balance zeroed with the stopped rotor in place each time.",
   "physicsNeeded": "If blades act independently, thrust should rise in proportion to the number of blades, F ∝ N. At high N the blades pass through each other's disturbed air and the plot should curve below the straight line. Plot F against N and compare with a line through the origin.",
   "slVsHl": "SL: linear plot and simple discussion of the departure. Top band: use the deviation to estimate an interference effect and quantify with residuals; consider tip vortices.",
   "whereMarksAreLost": "Research design: extra blades add load so rpm drops unless it is corrected each time. Conclusion: claiming proportionality without testing the intercept. Evaluation: no discussion of air recirculation.",
   "dataNote": "Keeping rpm constant needs retuning the supply for every N, which is fiddly but doable.",
   "verdict": "An easy build with a decent physics idea behind it (blade interference). The twist is to predict the curve before measuring."
  },
  {
   "id": "object-mass-and-buoyant-force-at-fixed-volume",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Object mass and buoyant force at fixed volume",
   "researchQuestion": "How does the mass of a fully submerged object of fixed volume (50 cm³, from 50 g to 400 g in 6 steps) affect the apparent weight and the water volume displaced?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Mass of the object, 50 to 400 g, using sealed 50 cm³ containers filled with different amounts of sand or steel shot; six values, 5 repeats each.",
   "dependentVariable": "Volume of water displaced in a measuring cylinder or overflow can (±0.5 cm³), and apparent weight from a force sensor or newton meter; buoyant force calculated.",
   "controlledVariables": "Same container volume and shape; water at the same temperature and depth; fully submerged with the same dry container each time; the same overflow can.",
   "physicsNeeded": "Archimedes: buoyant force = ρVg, which depends on the submerged volume, not mass. Plot displaced volume against mass and expect a horizontal line. Also plot apparent weight against mass, with gradient g and intercept −ρVg.",
   "slVsHl": "SL: show displaced volume is constant and buoyant force equals the weight of the displaced water. Top band: use a range of fluid densities such as salt solutions to show that the force depends on ρ.",
   "whereMarksAreLost": "Research design: the hypothesis is trivial, giving a flat line with no new physics. Data analysis: air bubbles and meniscus reading. Evaluation: no comment on the result being expected.",
   "dataNote": "Needs a measuring cylinder, balance and newton meter or sensor; the main uncertainty is reading the meniscus and trapped air bubbles.",
   "verdict": "A weak choice as it is, because the answer is known. Change the fluid density as the independent variable instead and it becomes a real investigation."
  },
  {
   "id": "pitch-angle-of-a-card-rotor-and-its-thrust",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Pitch angle of a card rotor and its thrust",
   "researchQuestion": "How does the pitch angle of blades on a small motor-driven rotor, from 5° to 45° in steps of 10°, affect the thrust recorded on a top-pan balance at constant motor voltage?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Blade pitch angle: 5°, 15°, 25°, 35°, 45°, set with a protractor jig, 3 repeats each.",
   "dependentVariable": "Balance reading loss (g) with the rotor running, converted to thrust in N; rotor rpm from a slow motion video to check the speed stays similar.",
   "controlledVariables": "Supply voltage, from a stabilised supply. Blade area and length, cut from one template. Rotor height above the pan, fixed by a clamp. Room draughts, reduced by closing doors and windows.",
   "physicsNeeded": "Air deflected downward gives a thrust from the momentum change, but pitch also changes the rotor speed because drag torque changes. Plot thrust against sin of pitch angle, or against angle, and look for a peak. Stall at large angles gives a maximum, which is the interesting result.",
   "slVsHl": "SL: describe the trend and suggest a reason for the peak. Top band: model thrust with a simple momentum argument and account for rpm changes by plotting thrust against rpm² for each angle.",
   "whereMarksAreLost": "Research design: rpm changes with angle and is not controlled or recorded. Data analysis: forcing a linear fit onto data with a maximum. Evaluation: setting the angle by eye with about ±3° uncertainty and not stating it.",
   "dataNote": "A protractor jig gives about ±2° in pitch, and a motor's rpm drops with more load, so record it every run.",
   "verdict": "Good if you accept that the result is a curve with a peak, not a clean law. The twist: report thrust per unit rpm² so pitch is separated from speed."
  },
  {
   "id": "projectile-mass-and-swing-of-a-ballistic-pendulum",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Projectile mass and swing of a ballistic pendulum",
   "researchQuestion": "How does the mass of a plasticine or steel projectile, from 5 g to 30 g in 6 steps, affect the maximum rise in height of a 500 g block pendulum after it embeds, with launch speed fixed by a spring gun?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Projectile mass, 6 values, 5 repeats each. Use a spring launcher compressed to a fixed mark, or a ramp roll to keep speed constant.",
   "dependentVariable": "Maximum height of the pendulum from a video frame against a ruler, or from the angle of the string; h = L(1 − cos θ). Launch speed inferred from the height.",
   "controlledVariables": "Launch speed (same spring compression, checked with light gates). Pendulum block mass and string length. Method of catching (the same foam target). Alignment at the centre of mass of the block.",
   "physicsNeeded": "Momentum conservation m v = (m + M)V, then (m + M)gh = ½(m + M)V². So v = ((m + M)/m)√(2gh). Plot h against (m/(m + M))² to get a straight line if v is fixed; the gradient is v²/2g.",
   "slVsHl": "SL: measure h for each mass and compare to the momentum prediction. Stronger: derive the linear graph, find v and compare with the light gate value, and calculate the kinetic energy lost.",
   "whereMarksAreLost": "Research design: launch speed not fixed when the mass changes. Data analysis: missing the m/(m + M) relationship. Evaluation: not checking that the block swings in plane, without rotation.",
   "dataNote": "Needs a spring launcher and camera; the launch speed variation with mass is the main uncertainty.",
   "verdict": "A classic that works well when you check the launch speed with a light gate, which is the bit many students skip. Use the linear graph to get v."
  },
  {
   "id": "puck-collisions-in-two-dimensions-with-video",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "HL",
   "title": "Puck collisions in two dimensions with video",
   "researchQuestion": "How does the impact parameter (0 to 4.0 cm in 0.5 cm steps, 9 values) affect the angle between the two pucks after a glancing collision on an air table?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Impact parameter, set by offsetting the target puck from the line of the moving puck; 0 to 4.0 cm in 9 steps, each repeated 3 to 5 times.",
   "dependentVariable": "Overhead video at 60 fps or more, digitised with Tracker. The angle between the two outgoing paths is measured, and the total momentum x and y components before and after are calculated.",
   "controlledVariables": "Launch speed: same launcher and start distance. Surface: air table or glass with dry ice or air puck, kept level. Puck masses: equal pucks checked on a balance. Camera: mounted directly above with a scale in view.",
   "physicsNeeded": "Vector momentum conservation gives p = p₁' + p₂' in x and y. For equal masses in an elastic collision the outgoing angle is 90°. Plot separation angle against impact parameter and compare with the prediction. Also plot total final momentum against initial momentum, gradient 1.",
   "slVsHl": "SL students can do a simple version with pucks of the same mass. HL work resolves components, checks energy loss and uses unequal masses. Top band analysis includes propagation of uncertainty from the tracked points.",
   "whereMarksAreLost": "Research design: the impact parameter is not measured and cannot be controlled by eye. Data analysis: using only speeds and not vectors. Evaluation: ignores that pucks are slowed by friction between frames.",
   "dataNote": "An air table or very smooth surface plus a camera is required; the main uncertainty is friction and the perspective of the video.",
   "verdict": "Impressive if you have the equipment, but hard to get clean data without an air table. Without one, choose a different collision topic."
  },
  {
   "id": "rolling-resistance-of-a-cart-with-added-load",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Rolling resistance of a cart with added load",
   "researchQuestion": "How does the total mass of a dynamics cart, increased from 0.50 kg to 2.00 kg in six steps, affect the coefficient of rolling resistance on a level wooden track?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Total cart mass from 0.50 kg to 2.00 kg using added masses (6 values, 3 repeats each).",
   "dependentVariable": "Force sensor reading while towing the cart at constant speed, or the tilt angle at which it just rolls at steady speed (measured with a protractor and metre rule for height). The coefficient is F/(mg) or tan θ.",
   "controlledVariables": "Track surface: the same board, cleaned and levelled between runs. Speed: a constant tow speed checked with video or a motion sensor. Wheels and axles: the same cart, same tyre pressure if applicable. Load position: added masses placed centrally each time.",
   "physicsNeeded": "Rolling resistance force F_r = C_rr N, with N = mg. Plot F_r against mg; the gradient is C_rr and a non-zero intercept shows a load independent term such as axle friction. Compare with the incline method where C_rr = tan θ.",
   "slVsHl": "SL: measure F_r at each mass and find C_rr from the gradient. Top band: test whether C_rr really is constant and compare two independent methods (tow and incline). HL is not required.",
   "whereMarksAreLost": "Research design: pulling at varying speed so the force is not equilibrium. Data analysis: forcing the line through the origin. Conclusion: not separating rolling from axle friction. Evaluation: ignoring track unevenness and its effect on the spread.",
   "dataNote": "A force sensor and a dynamics cart make it easy; small forces of a few tenths of a newton mean zero offset dominates the uncertainty.",
   "verdict": "Practical and clean, and the two-method comparison makes it stand out. Choose it if you like a simple set-up with a real analysis challenge."
  },
  {
   "id": "rotor-blade-area-and-thrust-from-a-small-spinning-rotor",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Rotor blade area and thrust from a small spinning rotor",
   "researchQuestion": "How does the plan area of a two-blade card rotor, varied from 10 cm² to 50 cm² in five steps, affect the thrust measured on a top-pan balance at a fixed motor speed of 1500 rpm?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Plan area of each blade cut from identical card, 10, 20, 30, 40 and 50 cm², with 3 repeats per area (new blades each time).",
   "dependentVariable": "Apparent loss in balance reading (g) while the rotor spins above the pan, converted to thrust in N (F = Δm × g). Rotor speed checked with a phone slow motion video or a stroboscope app.",
   "controlledVariables": "Motor speed, held by a stabilised DC supply and checked by video count each run. Blade pitch, set with a card template at 15°. Blade length, cut identically. Distance of rotor from the floor and walls, fixed with a clamp.",
   "physicsNeeded": "Thrust comes from the rate of change of momentum of the air pushed down, F = Δp/Δt = ρAv². Plot thrust against blade area and test for a straight line through the origin. The gradient links to ρv² for the air. Note that 'cross-sectional' is ambiguous, so define it as plan area.",
   "slVsHl": "SL: measure, plot, discuss proportionality and repeat scatter. Top band: estimate the downward air speed from the gradient and check it independently with an anemometer, and discuss why thrust may saturate at large area. HL depth is not required.",
   "whereMarksAreLost": "Research design: area and mass of the blades change together, so balance changes may come from weight of the rotor, not thrust. Data analysis: ignoring uncertainty from a fluctuating balance reading. Evaluation: not addressing air recirculation and ground effect.",
   "dataNote": "Needs a small motor, a supply and a 0.01 g balance; the balance reading fluctuates by about ±0.2 g because of turbulence, so take a mean over 10 s.",
   "verdict": "Workable once you fix the vague 'cross-sectional area' and separate thrust from blade weight. Choose it only if you enjoy building; the twist is to zero the balance with the rotor stopped for each blade set."
  },
  {
   "id": "rubber-temperature-and-the-friction-needed-to-start-sliding",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Rubber temperature and the friction needed to start sliding",
   "researchQuestion": "How does the temperature of a rubber block, from 5°C to 65°C in steps of 10°C, affect the coefficient of static friction on a wooden plank, found from the angle at which the block first slides?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Rubber temperature: 5, 15, 25, 35, 45, 55 and 65°C, achieved with an ice bath, room air and a water bath, with 5 repeats each.",
   "dependentVariable": "Critical angle θ at which the block first slips on a slowly raised plank, measured with a protractor or phone level app (±0.5°); μs = tan θ.",
   "controlledVariables": "Rubber sample and the surface, one block, one plank, wiped and dried between runs. Normal force, kept constant with the same block and no added mass. Rate of raising the plank, slow and steady with a screw jack. Time from taking the block out to testing, under 20 s, with a thermometer or an infrared thermometer checking the block temperature at the moment of release.",
   "physicsNeeded": "At the point of slipping, the friction force equals μs N, giving μs = tan θ for a block on an incline. Plot μs against temperature and look for a trend. Rubber becomes softer when warmer, which increases the true contact area and adhesion.",
   "slVsHl": "SL: measure and describe the trend with uncertainties from repeats. Top band: model the cooling of the block during the test, and explain the trend with the ideas of contact area and viscoelasticity.",
   "whereMarksAreLost": "Research design: the sample cools or warms in the air before the test, and water films on the surface change friction. Data analysis: a small range of angles with only ±0.5° resolution. Evaluation: not repeating with a new block to check sample variation.",
   "dataNote": "Needs a thermometer, a water bath and a tilting plank; the largest uncertainty is temperature change of the block between bath and test.",
   "verdict": "An unusual and personal idea if you control the cooling problem. The twist: measure the block's surface temperature with an infrared thermometer at the moment of slip."
  },
  {
   "id": "sag-of-a-ruler-bridge-with-changing-width",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Sag of a ruler bridge with changing width",
   "researchQuestion": "How does the width w (1.0, 1.5, 2.0, 2.5, 3.0, 4.0 cm) of a card or plastic strip bridge, supported at two points 30.0 cm apart, affect its central deflection under a 100 g load?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Width of the strip, 6 values, cut from one sheet of uniform plastic or thin wood so thickness is constant, with 3 repeat strips of each.",
   "dependentVariable": "Central deflection measured with a ruler against a mirrored scale or a dial gauge, and the difference between loaded and unloaded position. Calculated from it is the effective flexural stiffness.",
   "controlledVariables": "Span: fixed by two supports at 30.0 cm. Thickness: measured with a micrometer for every strip. Load: same hanging mass, placed at the centre by the same loop. Material: cut from the same sheet, same grain direction.",
   "physicsNeeded": "For a beam, deflection δ = FL³/(48EI) with I = wt³/12, so δ ∝ 1/w. Plot δ against 1/w: a line through the origin with gradient FL³/(4Et³), and E can be calculated. Beam bending is beyond the syllabus, but Hooke's law and Young modulus at SL and HL give the base, and the formula can be quoted with a source.",
   "slVsHl": "SL: show the inverse relation and describe stiffness. Higher: extract Young modulus E from the gradient and compare with a data book value, then discuss the assumption of small deflection and elastic behaviour.",
   "whereMarksAreLost": "Research design: varying width only by cutting different materials, or not repeating. Data analysis: tiny deflections measured with a ruler have large percentage uncertainty. Conclusion: stating 'wider means less sag' without a quantified relation. Evaluation: not checking permanent deformation or support slipping.",
   "dataNote": "Rulers, clamps, slotted masses and a micrometer are enough; a dial gauge helps, but deflection resolution is the main uncertainty.",
   "verdict": "A sound project if you use the 1/w plot and find E. Personalise by building an actual model bridge and comparing with the beam theory prediction. Without the linearisation it is too descriptive."
  },
  {
   "id": "siphon-tube-bore-and-water-flow-rate",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Siphon tube bore and water flow rate",
   "researchQuestion": "How does the internal diameter of a siphon tube (4 to 12 mm, 6 sizes) affect the volume flow rate of water at a fixed height difference of 30 cm?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Internal diameter of clear tubing, 6 sizes from 4 mm to 12 mm, measured with a calliper or by a water column of known length. Three runs each.",
   "dependentVariable": "Volume of water collected in a measuring cylinder over a timed interval with a stopwatch; flow rate Q = V / t, in ml per s.",
   "controlledVariables": "Height difference between the water levels, held with a marked stand and a large supply tank kept topped up. Tube length, the same 1 m for all, or the effect of length is shown separately. Water temperature, from a thermometer. Tube kept straight with no kinks.",
   "physicsNeeded": "Bernoulli gives an ideal exit speed v = sqrt(2 g h), so Q = A v = pi d^2 v / 4. Plot Q against d^2; the gradient gives an effective speed to compare with sqrt(2 g h). Narrow tubes will fall below this because of viscosity, so also test the Poiseuille prediction Q proportional to d^4.",
   "slVsHl": "SL: Q against d^2 with uncertainty and comparison to the ideal speed. Top band: discuss Reynolds number, plot log Q against log d to find the real power and explain which regime applies. Still fine at HL, since the syllabus needed is small.",
   "whereMarksAreLost": "Research design: letting the water level in the tank fall so the height changes. Data analysis: assuming the area law without testing it. Evaluation: not explaining why the measured speed is well below the ideal value.",
   "dataNote": "Standard clear tubing, a bucket and a measuring cylinder are enough; the main uncertainty is the tank level dropping and bubbles in the tube.",
   "verdict": "Simple and practical, but only scores well if you test the power law and explain any deviation. Use a log-log plot as your personal analytical twist."
  },
  {
   "id": "sliding-friction-of-a-ball-on-artificial-turf-with-different-water-dep",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Sliding friction of a ball on artificial turf with different water depth",
   "researchQuestion": "How does the depth of water sprayed on a turf sample (0 to 5 mL per 100 cm², 6 values) affect the coefficient of kinetic friction of a rolling or sliding football, found from its stopping distance from a fixed launch speed?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Volume of water sprayed on a turf strip, 0 to 5 mL per 100 cm² in 6 steps, measured with a syringe. Five repeats each. The original range in millimetres is not realistic for a school lab.",
   "dependentVariable": "Stopping distance of a ball launched down a ramp of fixed height onto the horizontal turf, measured with a metre rule or video. Launch speed v from energy on the ramp, then μ = v²/(2gd) for sliding, or an effective resistance coefficient for rolling.",
   "controlledVariables": "Launch speed: same ramp release height each time, checked by light gates or video. Ball: same ball and inflation pressure. Turf: same sample, dried and combed between trials to keep pile orientation the same. Surface levelness: checked with a spirit level.",
   "physicsNeeded": "Work done by friction: μmg·d = ½mv², so d = v²/(2μg). Plot 1/d against water volume, or μ against water volume, and look for a trend. For rolling balls the loss is rolling resistance, not sliding friction, so state this and treat the coefficient as an effective value.",
   "slVsHl": "SL: measure distances, compute μ and describe the trend. Top band: distinguish rolling from sliding using ½mv² + ½Iω² for a hollow sphere, and test whether the results follow a simple law of water volume.",
   "whereMarksAreLost": "Research design: a rolling ball does not have a kinetic friction coefficient, and the student does not notice. Data analysis: μ averaged across rough repeats without spread. Conclusion: overclaim from a small trend. Evaluation: turf drying and pile direction changing during the session.",
   "dataNote": "Needs a ramp, metre rule, spray or syringe and a turf offcut; the main uncertainty is that the wet surface is not uniform and dries in minutes.",
   "verdict": "Good sporty idea if you clearly say rolling resistance and not sliding friction. Twist: use your own football and a pitch offcut, and relate it to why wet pitches play faster or slower."
  },
  {
   "id": "sliding-friction-of-a-block-on-six-surface-materials",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Sliding friction of a block on six surface materials",
   "researchQuestion": "How does the kinetic friction coefficient of a 500 g wooden block change when it is pulled at constant speed over six different surface materials (sandpaper, cardboard, felt, rubber mat, acrylic sheet, aluminium foil on board), measured with a force sensor from 0.5 N to 5 N of normal load?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Normal force on the block, changed by adding masses of 100 g steps from 0 to 500 g (6 values), repeated on each of 3 chosen surface materials. Optionally extend to 6 materials at one fixed load. Each setting repeated 5 times.",
   "dependentVariable": "Pulling force read from a digital force sensor (or a newton meter) while the block moves at steady speed, taken as the mean of the flat part of the trace. Kinetic friction coefficient is the gradient of friction force against normal force, with uncertainty from the best and worst fit lines.",
   "controlledVariables": "Pulling speed: motor-driven pulley or a marked timing of about 5 cm/s, checked with a video and ruler. Contact area: same block face used every time. Surface cleanliness: wipe and use a fresh area of material for each run. Pull angle: string kept parallel to the surface using a pulley or a level-set sensor height.",
   "physicsNeeded": "Kinetic friction F = μk N when acceleration is zero, so pulling force equals friction. Plot friction force (y) against normal force (x). The line should be straight through the origin and the gradient is μk. An intercept that is not zero suggests a systematic error such as sensor offset or adhesion. Compare gradients between materials.",
   "slVsHl": "SL: measure, plot, get μk for each material and compare with a sensible uncertainty. Top band: test whether F really is proportional to N by looking at the intercept, check speed independence with a second set of speeds, and comment on stick slip. HL depth can come from an inclined plane comparison method or a model of energy lost to friction, but this is not needed for the syllabus.",
   "whereMarksAreLost": "Research design: too many materials with only one load and no repeats, or failing to hold speed steady so static and kinetic friction get mixed. Data analysis: calculating μ from single readings instead of a gradient, and ignoring the intercept. Conclusion: stating that a material has a coefficient with no comparison to a data book value. Evaluation: not discussing stick slip jerks, surface wear and non-uniform speed.",
   "dataNote": "Needs a force sensor or a 10 N newton meter, wooden block, masses and test surfaces; the main uncertainty is keeping a truly constant speed by hand, so a motor or a sensor trace is better.",
   "verdict": "A very common and safe topic, so it will only stand out if you make it rigorous. The twist is to choose surfaces you actually care about, for example different climbing shoe rubbers or skate deck grips, and test proportionality properly rather than one load per material."
  },
  {
   "id": "sphere-density-and-settling-time-in-water",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Sphere density and settling time in water",
   "researchQuestion": "How does the density of a sphere of fixed radius (1000 to 7800 kg m^-3, 6 materials) affect its terminal speed when sinking through glycerol in a 1 m measuring cylinder?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Density of 12 mm diameter spheres: nylon, glass, aluminium, titanium or ceramic, steel, brass. 6 materials, 5 drops each. Density found from mass and diameter.",
   "dependentVariable": "Time to fall between two marked lines, measured with a phone video at 240 fps or 60 fps and frame-by-frame analysis. Terminal speed = distance / time. Also compare with the Stokes prediction.",
   "controlledVariables": "Sphere diameter, checked with a micrometer at several angles. Liquid temperature, measured with a thermometer before each drop. Release point, by dropping from just under the surface. Tube width, one tube for all runs. Note that water is too fast, so use glycerol or a glycerol/water mix.",
   "physicsNeeded": "At terminal speed, weight = buoyancy + drag, so (rho_s - rho_f) g V = 6 pi eta r v for slow flow. Plot v against (rho_s - rho_f). It should be a straight line through the origin with gradient 2 g r^2 / (9 eta), so eta can be extracted and compared with the data book value.",
   "slVsHl": "SL: straight-line graph and a viscosity value with uncertainty. Top band: check the Reynolds number, apply the wall correction for the tube radius, and discuss why the line curves for dense spheres at high speed. HL is not required.",
   "whereMarksAreLost": "Research design: using water so the fall is too quick to time, or letting the density change together with size. Data analysis: timing by stopwatch with reaction-time error swamping the data. Evaluation: ignoring that spheres have not reached terminal speed and ignoring wall effects.",
   "dataNote": "Needs glycerol, spheres of different materials and a video for timing; the main uncertainty is whether terminal speed is reached and the temperature-dependent viscosity.",
   "verdict": "Worth choosing if you switch to a viscous liquid and measure speed rather than a vague equilibrium time. The twist is using your measured viscosity to check the Stokes model and say where it breaks."
  },
  {
   "id": "sphere-diameter-and-fall-time-with-quadratic-drag-model",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Sphere diameter and fall time with quadratic drag model",
   "researchQuestion": "How does the diameter of a spherical projectile (from 2 cm to 20 cm in 2 cm steps) dropped from 50 m affect its fall time in a numerical model with quadratic air drag and a fixed drag coefficient?",
   "dataDifficulty": 2,
   "dataSource": "simulation",
   "sitesListingIt": 1,
   "independentVariable": "Sphere diameter from 2 cm to 20 cm in 10 values in the model, at a fixed density such as iron; repeat with a different density to check.",
   "dependentVariable": "Fall time from the model, found by stepping the equation of motion in a spreadsheet or Python with a time step of 0.001 s, and checked against the analytical solution using a tanh function. A real check can be made by dropping balls of different sizes from a stairwell and timing them with a video.",
   "controlledVariables": "Drag coefficient fixed at 0.47; air density 1.2 kg/m³; fall height fixed; time step tested for convergence by halving it.",
   "physicsNeeded": "m dv/dt = mg − ½ρ_air C_d A v², with m = ρ_s(4/3)πr³ and A = πr², so the terminal speed scales as √(r). Plot fall time against diameter, and terminal speed squared against diameter, whose gradient tests the model. Small spheres are drag-limited and large ones approach free fall.",
   "slVsHl": "An SL student can build the step-by-step model and describe the trend. Top band work compares with the analytic solution, validates against real drops, and discusses the change in C_d with Reynolds number.",
   "whereMarksAreLost": "Research design: purely computational work with no validation against real data. Data analysis: uncertainty not treated, since simulation has no random error but has step-size error. Evaluation: constant C_d assumption not challenged.",
   "dataNote": "Needs a spreadsheet or Python; the main uncertainty is numerical step size and the assumed C_d, so test convergence and vary C_d.",
   "verdict": "Only worth it if you add real drops to validate the model, otherwise it reads as a coding exercise. Make it personal with balls you can actually drop, such as steel, wooden and foam spheres."
  },
  {
   "id": "tension-in-a-whirled-bung-at-different-radii",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Tension in a whirled bung at different radii",
   "researchQuestion": "How does the radius r of a rubber bung swung in a horizontal circle (r = 0.30 to 0.90 m in 6 steps) affect the centripetal force needed to keep the period fixed at 1.0 s?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Radius r of the circle, 0.30, 0.40, 0.50, 0.60, 0.75, 0.90 m, with 5 trials at each.",
   "dependentVariable": "Centripetal force from the weight of hanging washers on the string below a glass tube (F = Mg), balanced when the marker on the string stays at the tube. Period from a phone video at 240 fps or by timing 20 revolutions with a stopwatch.",
   "controlledVariables": "Period fixed at 1.0 s by timing over many revolutions and adjusting the swing. Mass of the bung: same bung throughout. Circle kept horizontal by checking the angle of the string in video. Hanging mass changed only to find the balance point.",
   "physicsNeeded": "F = m·4π² r / T². At fixed T, plot F against r; the gradient equals 4π² m / T², so m can be compared with the balance reading. Also possible to vary T at fixed r and plot F against 1/T².",
   "slVsHl": "SL students can get a full mark spread with the linear graph and a comparison of the gradient with the mass. Top band work handles the fact that the string is not horizontal, which needs the vertical component of the tension, and shows that the effective radius is measured from the tube to the centre of mass of the bung.",
   "whereMarksAreLost": "Research design: holding speed constant is hard; fixing the period is much easier and should be said clearly. Data analysis: string angle ignored. Evaluation: judging the period by eye instead of timing many revolutions.",
   "dataNote": "Only a bung, string, glass tube, washers and a stopwatch are needed; the main uncertainty is the sag angle of the string and keeping T constant by hand.",
   "verdict": "Simple and safe, though standard, so it needs a personal angle: quantify the sag angle and correct for it. Wear eye protection and swing in an empty area."
  },
  {
   "id": "terminal-speed-of-falling-balls-of-different-mass-in-air",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Terminal speed of falling balls of different mass in air",
   "researchQuestion": "How does the mass of a hollow plastic ball of fixed diameter (2.0, 3.0, 4.0, 5.0, 6.0, 8.0 g) affect its terminal speed and drag coefficient when dropped from 3 m?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Mass of the ball, 6 values from 2 to 8 g, adjusted by adding modelling clay or beads inside identical hollow balls (e.g. table tennis or foam balls), each dropped 5 times.",
   "dependentVariable": "Position against time from video at 120 fps or more, analysed in Tracker, with terminal speed from the gradient of the final linear section. Drag coefficient is then calculated as C = 2mg / (ρAv²).",
   "controlledVariables": "Ball diameter: same shell each time, checked with a calliper. Drop height: fixed, with a stairwell or balcony giving at least 3 m. Air: indoor, no draughts, with temperature recorded for air density. Camera position: fixed and perpendicular, with a metre rule in view for scale.",
   "physicsNeeded": "At terminal speed mg = ½CρAv². Plot v² against m: a line through the origin with gradient 2g/(CρA), so C follows from the gradient. If C is constant, the graph is linear, and if not it shows dependence on Reynolds number.",
   "slVsHl": "SL: find v_t for each mass and show that v² is proportional to m. Top band: compute C with uncertainty, check Reynolds number, and discuss why C is not expected to depend on mass but might change with speed.",
   "whereMarksAreLost": "Research design: the ball may not reach terminal speed within the drop height, and that is not checked. Data analysis: perspective and frame rate errors. Conclusion: stating that mass changes C when the data are within error. Evaluation: ignoring that uneven mass added inside changes spin and path.",
   "dataNote": "Needs a slow motion phone camera and Tracker; the biggest uncertainty is whether terminal speed is really reached.",
   "verdict": "Good if you accept that the expected answer is 'C stays constant'. That makes the conclusion honest and interesting. Personalise by dropping from a real stairwell and using coffee filters as an extension."
  },
  {
   "id": "terminal-speed-of-paper-cones-against-weight-per-area",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Terminal speed of paper cones against weight per area",
   "researchQuestion": "How does the ratio of mass to frontal area (from 0.5 to 3.0 g per cm², 6 values) affect the terminal speed of cone shaped paper cases falling through air?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Mass divided by frontal area, changed by stacking 1 to 6 identical coffee filter cups and using a balance to check the mass. Each value repeated 5 times.",
   "dependentVariable": "Fall time over the last 1.0 m of a 3 m drop, using a phone recording at 120 fps beside a metre rule. Terminal speed is the distance divided by time, with the uniform speed section confirmed on the video.",
   "controlledVariables": "Shape: same cup type, nested so the outline is unchanged. Release height and orientation: released from a fixed mark, apex down. Air movement: indoor stairwell with doors closed. Air temperature: read from a thermometer.",
   "physicsNeeded": "At terminal speed weight equals drag, mg = ½CρAv², so v = √(2mg/CρA). Plot ln v against ln(m/A) and find the gradient. Compare it to 0.5 rather than assuming the value. Then plot v² against m/A to get C from the gradient.",
   "slVsHl": "SL students can plot v² against m/A and comment on linearity. Top band work fits the exponent with uncertainty and discusses drag at low Reynolds numbers where the power changes. HL depth can come from discussing Reynolds number and the change in drag regime.",
   "whereMarksAreLost": "Research design: cones are dropped before terminal speed is reached. Data analysis: assumes the exponent is 0.5 without fitting. Evaluation: sticks to random errors and ignores drafts and cups deforming when stacked.",
   "dataNote": "Coffee filters, a balance, a phone and a stairwell are enough; the main uncertainty is timing and drafts.",
   "verdict": "An accessible idea that can still score well if you fit the exponent honestly. Do not choose it only for its simplicity, since many students have already done this."
  },
  {
   "id": "terminal-speed-of-paper-parachutes-of-varying-radius",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Terminal speed of paper parachutes of varying radius",
   "researchQuestion": "How does the radius of a circular paper or plastic parachute (5.0, 7.5, 10.0, 12.5, 15.0, 20.0 cm) with a fixed 20 g load affect its terminal speed when dropped from 2.5 m?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Canopy radius, 6 values, cut from the same sheet, each dropped 5 times.",
   "dependentVariable": "Terminal speed from a video analysed in Tracker (position against time, gradient of the linear section), or from the time to fall a marked final 1 m section with a stopwatch.",
   "controlledVariables": "Load: same plasticine mass, attached with strings of equal length. Canopy material: cut from one sheet, checked for flatness. Drop height and release: from a fixed height, released by hand at rest. Air: indoors with the doors shut, no fans.",
   "physicsNeeded": "At terminal speed mg = ½CρAv², so v ∝ 1/r if C is constant. Plot v² against 1/r² (or 1/A): a straight line through the origin, and the gradient gives 2mg/(Cρπ). The line shows C and can be compared with a typical value of about 0.75 to 1.4 for a parachute.",
   "slVsHl": "SL: measure v_t, plot the linearised graph and calculate C. Top band: check the Reynolds number range, discuss canopy shape changes at larger radius, and the fact that the load's own drag is not negligible for small canopies.",
   "whereMarksAreLost": "Research design: dropping from too low, so terminal speed is not reached. Data analysis: reading speed from a stopwatch over short distances. Conclusion: claiming 'proportional' from only a curve. Evaluation: not commenting on canopy tilting or oscillation.",
   "dataNote": "A stopwatch and ruler work, but a phone video and Tracker reduce timing uncertainty; the canopy swaying is the main problem.",
   "verdict": "A common idea in the physics of drag, so it needs a personal angle. Compare a flat with a hemispherical canopy, or vary the load as well. Do the v² against 1/A plot to reach the top band."
  },
  {
   "id": "tilt-angle-measurement-of-static-friction-for-six-material-pairs",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Tilt-angle measurement of static friction for six material pairs",
   "researchQuestion": "How does the coefficient of static friction, from the critical tilt angle, differ for a wooden block on six surfaces (wood, glass, aluminium, sandpaper, rubber, felt)?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Surface material of the incline: 6 surfaces, each with 8 trials. A further test varies the normal force by adding masses to the block from 0.2 kg to 1.0 kg.",
   "dependentVariable": "Angle at which the block begins to slide, from a protractor or a phone inclinometer, tilted slowly. Coefficient mu_s = tan(theta).",
   "controlledVariables": "Same block with the same contact face and area. Surface cleaned before each trial. Same tilting rate, ideally by a lab jack raising one end. Same mass on the block (or measured across a set of masses). Humidity and temperature noted.",
   "physicsNeeded": "At the point of slipping, mg sin(theta) = mu_s mg cos(theta), so mu_s = tan(theta). For mass variation, use a horizontal pull with a force meter: plot F_max (y) against normal force N (x), the gradient is mu_s.",
   "slVsHl": "SL students compare mu_s among materials with uncertainties. Higher marks come from showing that mu_s does not depend on the normal force or the area, and from analysing the spread from surface wear.",
   "whereMarksAreLost": "Research design: raising the ramp at an uneven speed so that the angle is hard to read. Data analysis: averaging without treating the trial spread as uncertainty. Evaluation: not seeing that the surface changes with repeated sliding.",
   "dataNote": "Needs a board, block, protractor or phone app and surface sheets; main uncertainty is deciding when sliding starts, about 1 to 2 degrees.",
   "verdict": "Easy and safe, but the question is only a comparison. Add the force meter graph and test the friction law to make it a proper investigation."
  },
  {
   "id": "trolley-acceleration-with-fixed-total-mass",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Trolley acceleration with fixed total mass",
   "researchQuestion": "How does the driving force from a hanging mass (0.02 to 0.12 N in steps of 0.02 N, 6 values) affect the acceleration of a trolley on a level track when the total mass is kept at 0.500 kg?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Hanging weight from 2 g to 12 g, moved one slice at a time from the trolley to the hanger. Each value repeated at least 5 times.",
   "dependentVariable": "Velocity at two light gates on the track, or a motion sensor v–t plot. Acceleration comes from the gradient of the v–t graph or from (v² − u²)/2s.",
   "controlledVariables": "Total mass: all slotted masses stay on the system and are checked on a balance. Track level: checked with a spirit level. Friction: same wheels and track, string parallel to track. Start position: fixed mark.",
   "physicsNeeded": "For the system, mg = (M + m)a with M + m constant, so a is proportional to m. Plot a against the driving force. The gradient is 1/(total mass) and any non-zero intercept shows friction, which can be used to estimate a friction force.",
   "slVsHl": "SL students can verify the gradient against the total mass. Higher marks come from using the intercept to quantify friction and from checking string and pulley effects. HL students can consider the rotational inertia of the pulley in the gradient.",
   "whereMarksAreLost": "Research design: the total mass is not really constant since masses are not weighed. Data analysis: only uses a single trial and no error bars. Conclusion: claims F = ma is proved with no comparison of gradient with 1/M.",
   "dataNote": "Uses a track, light gates or a motion sensor and a balance; the main uncertainty is friction and pulley effects.",
   "verdict": "A fair and reliable choice, but it is a school classic. Its value is in analysing the intercept and pulley mass carefully, not simply confirming F = ma."
  },
  {
   "id": "upthrust-on-an-aluminium-block-in-water-from-5-to-80-c",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Upthrust on an aluminium block in water from 5 to 80 °C",
   "researchQuestion": "How does the apparent weight of a fully submerged aluminium block change as water temperature rises from 5 °C to 80 °C in steps of about 15 °C, and does the upthrust change by more than measurement uncertainty?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Water temperature: 6 values from about 5 °C (ice bath) to 80 °C, measured with a thermometer next to the block. Five repeated weighings per temperature.",
   "dependentVariable": "Apparent weight of the block hung from a top-pan balance or force sensor while submerged. Upthrust is the true weight minus apparent weight, and is compared with ρgV using tabulated water density.",
   "controlledVariables": "Block volume: same block throughout, measured with a calliper (thermal expansion is small but can be discussed). Submersion: fully under, not touching walls, at the same depth. Water volume and container: same beaker, stirred so temperature is uniform. Thread: thin thread, same length, kept out of hot water where possible.",
   "physicsNeeded": "Upthrust F = ρ_fluid V g, with water density falling from 1000 to about 972 kg/m³ over this range. Plot measured upthrust against tabulated density; the gradient should equal Vg. The expected change is about 3%, so precision matters.",
   "slVsHl": "SL: measure the trend and compare with the density table. Top band: propagate uncertainty to show whether a 3% effect can be seen at all, and discuss the effect of convection currents and thermal expansion of the block.",
   "whereMarksAreLost": "Research design: balance resolution too coarse to see a 3% change. Data analysis: no uncertainty on upthrust as a difference of two masses. Conclusion: claiming a trend where the error bars overlap. Evaluation: convection currents and surface tension on the thread ignored.",
   "dataNote": "Needs a 0.01 g balance or sensitive force sensor and a large block; the main uncertainty is that the expected effect is only a few percent.",
   "verdict": "Fine and honest if you check first that your balance can see a 3% change. Twist: make the hot water case a swimming or bath link, and use a larger block to enlarge the signal."
  },
  {
   "id": "warming-a-lubricant-to-change-sliding-friction",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Warming a lubricant to change sliding friction",
   "researchQuestion": "How does the temperature of vegetable oil, varied from 20 °C to 60 °C in 10 °C steps, affect the coefficient of kinetic friction of a wooden block pulled at constant speed across a glass plate?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Oil temperature, 20, 30, 40, 50, 60 °C (5 values), each with 5 repeat pulls. Oil film heated in a water bath before being spread.",
   "dependentVariable": "Pulling force read from a force sensor (or a newton meter dragged by a motor) at constant speed; μk = F / (mg) from the mean force. Oil temperature checked with a digital thermometer just before each pull.",
   "controlledVariables": "Block mass and contact area (same block, same load). Oil volume and film thickness (measured with a syringe and spread with a fixed template). Pulling speed (motor or timed with video). Surface cleaned and re-oiled between runs.",
   "physicsNeeded": "F = μk R with R = mg on a horizontal surface. Plot μk against temperature, or ln μk against 1/T if testing an Arrhenius type viscosity trend. Gradient shows how sensitive friction is to viscosity change.",
   "slVsHl": "SL: measure, plot, describe the trend and discuss uncertainty. Stronger work links μk to viscosity, separates boundary from fluid lubrication, and justifies a model, rather than only reporting a trend.",
   "whereMarksAreLost": "Research design: oil cools during the run, so temperature is not really controlled. Data analysis: pulling force is jerky and the mean is taken without checking for stick slip. Evaluation: not asking whether μk is a valid quantity for a fluid film.",
   "dataNote": "Needs a force sensor and a heated bath; the oil cooling between heating and pulling is the main uncertainty in temperature.",
   "verdict": "Worth doing only if you accept that lubricated friction may not follow F = μR. Measure viscosity separately with a falling ball and you have a strong personal twist."
  },
  {
   "id": "water-flow-through-tubes-of-different-bore",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Water flow through tubes of different bore",
   "researchQuestion": "How does the internal diameter of a horizontal tube, varied from 2 mm to 8 mm using 6 tubes of equal length 30 cm, affect the volume flow rate of water driven by a constant head of 50 cm?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Internal tube diameter, 6 values from 2 mm to 8 mm, measured with a vernier caliper or a travelling microscope and repeated 3 times.",
   "dependentVariable": "Volume collected in a measuring cylinder over a set time, timed with a stopwatch, giving flow rate in mL s⁻¹. The flow is also checked by running for at least 30 s.",
   "controlledVariables": "Pressure head, kept constant by an overflow bucket or Mariotte bottle. Water temperature, checked with a thermometer since viscosity depends on it. Tube length, cut to the same length. Tube inlet and outlet height, fixed.",
   "physicsNeeded": "For laminar flow Poiseuille's law gives Q = πΔP r⁴/(8ηL), so Q ∝ d⁴. Plot Q against d⁴, and the gradient gives πΔP/(128ηL), allowing viscosity to be found. Check the Reynolds number, since turbulent flow breaks the relationship.",
   "slVsHl": "SL students plot log Q against log d and find the exponent, comparing it to 4. Top band work considers the range of laminar flow and the inlet effects, and finds the viscosity. Poiseuille's law goes beyond the syllabus, so the physics must be explained clearly.",
   "whereMarksAreLost": "Research design: the head falls as the container drains, so pressure is not constant. Data analysis: uncertainty in a small diameter is large and is raised to the fourth power. Conclusion: fitting a power without testing the exponent against the uncertainty. Evaluation: ignoring turbulence at large diameter and entrance effects.",
   "dataNote": "Needs rigid tubes of different bore, a constant head arrangement and a measuring cylinder. The main uncertainty is bore diameter and unsteady head.",
   "verdict": "A good one if you keep the head constant and check laminar flow. Twist: repeat with a glycerol and water mix to bring viscosity into the analysis."
  },
  {
   "id": "young-modulus-of-copper-wire-from-load-extension-graph",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Young modulus of copper wire from load extension graph",
   "researchQuestion": "What is the Young modulus of a 2.0 m length of copper or constantantan wire, found by adding masses from 0.5 kg to 4.0 kg in 0.5 kg steps and measuring the extension, and how does it compare with the accepted value?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Load applied to the wire, from 0.5 kg to 4.0 kg in 8 steps, loading and then unloading to check for elastic behaviour.",
   "dependentVariable": "Extension measured with a vernier scale, a travelling microscope or a ruler with a pointer (±0.1 mm). Wire diameter measured with a micrometer at several points. Young modulus from the gradient of stress against strain.",
   "controlledVariables": "Original wire length, measured from clamp to marker. Wire material and diameter, using one wire from the same reel. Temperature, kept at room level. Kinks removed by preloading with a small mass before starting.",
   "physicsNeeded": "E = stress/strain = (F/A)/(ΔL/L). Plot force against extension, so the gradient equals EA/L, and E = gradient × L/(πd²/4). Stay within the linear elastic region.",
   "slVsHl": "SL students get E from a straight line gradient and compare it. Top band work propagates the diameter uncertainty (squared in the area), identifies the limit of proportionality, and repeats with another wire. There is no HL syllabus need.",
   "whereMarksAreLost": "Research design: the stated variables are muddled, with force as independent but a stated aim to find E, and a short wire that gives tiny extensions. Data analysis: using a single diameter reading, which dominates the uncertainty. Conclusion: not checking elastic limit. Evaluation: ignoring the wire's slippage in the clamp and kinks.",
   "dataNote": "Needs a long thin wire, a strong clamp, a micrometer and a precise extension scale. The main uncertainty is diameter and small extensions.",
   "verdict": "Solid classic that works well if you use a long, thin wire. It is well known, so a twist helps: compare a wire before and after annealing with a hot flame, or across three different metals."
  },
  {
   "id": "young-modulus-of-wires-and-rubber-from-load-extension-data",
   "topic": "A.2",
   "topicName": "Forces and momentum",
   "level": "both",
   "title": "Young modulus of wires and rubber from load-extension data",
   "researchQuestion": "How does the Young modulus of copper, steel and nylon wires of equal diameter, found from load-extension gradients for loads of 0.5 N to 5.0 N in 0.5 N steps, compare with database values?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Wire material (copper, steel, nylon, three to four samples), and load added in 8 to 10 steps from 0.5 N to 5 N, each loaded and unloaded three times.",
   "dependentVariable": "Extension measured with a travelling microscope or a ruler against a fixed marker (mm); diameter measured with a micrometer at five points. Stress = F/A and strain = extension/original length are calculated.",
   "controlledVariables": "Original length: fixed clamp to marker distance measured with a metre rule. Diameter: micrometer check at several points. Temperature: same room, short runs. Load: kept under the elastic limit by checking the wire returns to zero extension.",
   "physicsNeeded": "Stress = F/A, strain = x/L, E = stress/strain. Plot stress against strain: the gradient in the linear region is the Young modulus. Rubber gives a curve with hysteresis, which is a useful contrast but cannot give a single E.",
   "slVsHl": "SL: get E for two or three wires and compare with tabulated values. Top band: propagate the diameter uncertainty (it enters squared), locate the limit of proportionality objectively, and discuss hysteresis and work done from the area under a force-extension graph.",
   "whereMarksAreLost": "Research design: overloading past the elastic limit, or a vague RQ about 'differences'. Data analysis: ignoring diameter uncertainty, which dominates. Conclusion: no comparison with an accepted value. Evaluation: not mentioning slipping at the clamp or the kinks in the wire.",
   "dataNote": "Long thin wires, a clamp, slotted masses and a travelling microscope are needed; the main uncertainty is the small extension (under 2 mm) and the wire diameter.",
   "verdict": "Worth choosing if you have a long wire and a good way to read tiny extensions. Make it personal by testing something unusual such as fishing line or guitar strings from your own instrument, and avoid the vague 'compare materials' framing."
  },
  {
   "id": "basketball-pressure-and-bounce-efficiency",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Basketball pressure and bounce efficiency",
   "researchQuestion": "How does the coefficient of restitution of a basketball, found from drop heights of 1.20 m, change when its gauge pressure is varied from 30 kPa to 80 kPa in 6 to 8 steps?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Gauge pressure, 30 to 80 kPa in 10 kPa steps (6 values), set with a hand pump and a pressure gauge, with 5 drops at each.",
   "dependentVariable": "Rebound height from a phone video filmed against a metre rule, or a sound-based method with a microphone timing successive bounces. The coefficient of restitution e is found from the ratio of rebound to drop height, then square-rooted.",
   "controlledVariables": "Drop height fixed with a release rig. Same ball and the same hard floor. The ball released without spin. Temperature of the ball stable, since air pressure depends on it.",
   "physicsNeeded": "e = v_after / v_before = √(h₂/h₁). Plot h₂ against h₁ for a fixed pressure to find e² from the gradient. Then plot e against pressure. Discuss energy loss as ΔE = mg(h₁ − h₂) and the ball's gas and rubber wall deformation.",
   "slVsHl": "SL students calculate e at each pressure and discuss the trend. To reach the top band, vary drop height at each pressure to get e from a gradient, and consider whether e levels off. HL can link to the gas laws for the pressure change during impact.",
   "whereMarksAreLost": "Research design: pressure changing as the ball is checked or pumped, or reading heights from a video without calibration. Data analysis: only one drop height. Conclusion: a trend claimed over too few pressures. Evaluation: air resistance and parallax not discussed.",
   "dataNote": "Needs a ball, a pump with a gauge and a phone camera; parallax reading of height is the main uncertainty.",
   "verdict": "Less crowded (listed on 2 sites) and easy to run. Choose it if you play basketball, and add multiple drop heights to turn it into a gradient measurement."
  },
  {
   "id": "rebound-of-a-bouncing-ball-from-freezer-to-hot-water",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Rebound of a bouncing ball from freezer to hot water",
   "researchQuestion": "How does the starting temperature of a tennis ball, varied from 5 °C to 60 °C in six steps, change its coefficient of restitution when it is dropped from 1.00 m onto a concrete floor?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Core temperature of the ball: about 5, 15, 25, 35, 45 and 60 °C (six values). Cool in a fridge or freezer, warm in a water bath or oven set low. Use one ball per temperature, or the same ball re-equilibrated, and do at least five drops at each value.",
   "dependentVariable": "Rebound height after the first bounce, read from a video recorded at 120 fps or 240 fps against a metre rule, or from sound timing between the first and second impacts with a microphone and Audacity. Coefficient of restitution e is calculated as the square root of rebound height divided by drop height. Ball temperature is checked with a digital or infrared thermometer just before release.",
   "controlledVariables": "Drop height fixed with a clamp-held release point and a plumb line. Same floor tile or slab for every drop, checked for cleanliness. Ball cooling during the transfer is limited by timing each drop within 10 s of removal and by logging the temperature immediately before release. The same ball, or balls from the same tube, are used to avoid differences in wear and internal pressure.",
   "physicsNeeded": "For a ball hitting a fixed surface, e = v_after / v_before = sqrt(h / H), because speed comes from energy conservation during free fall. Plot h against H for a fixed temperature to check that the relationship is linear, with gradient e squared. Then plot e against temperature, or e squared against temperature, and comment on the trend. Link the trend to the gas pressure inside the ball, which rises with temperature according to the pressure law, and to the softening of the rubber, which increases energy loss as internal friction in the material.",
   "slVsHl": "At SL, a clean e against temperature graph with uncertainty bars and a sensible explanation using energy dissipated in the collision is enough for a good mark. To reach the top band, repeat at several drop heights to show that e does not depend on H, then separate the pressure effect from the rubber effect, for example by comparing a pressurised ball with a pressureless one or by drilling a small hole in a sacrificial ball. An HL student can add a model of the energy lost per bounce as a fraction of the initial energy, and estimate the change in gas pressure from the pressure law with T in kelvin.",
   "whereMarksAreLost": "Research design: temperature of the ball surface is measured but the core is at a different temperature, so the real IV is unclear. Data analysis: only one drop per temperature, or rebound height read by eye from a rule with no frame by frame video, producing large unquantified uncertainty. Conclusion: claiming a linear trend from too narrow a temperature range without a fitted line, or explaining the trend with 'more energy' without discussing the ball's rubber and gas. Evaluation: ignoring how quickly a hot or cold ball returns to room temperature, and not discussing systematic error from slow motion video frame rate or parallax.",
   "dataNote": "A phone with slow motion video, a metre rule, a thermometer and a water bath are enough, but the ball cools or warms between the bath and the drop, so the real core temperature is the main uncertainty.",
   "verdict": "Popular with two sites listing it, so it needs a personal angle: I would push a student to compare a pressurised ball with a pressureless one, or to test a ball type they actually play with, so the physics explanation is tested and not just quoted. It works well because the equipment is cheap and the range of e is large enough to beat the noise."
  },
  {
   "id": "rolling-time-of-a-can-down-ramps-of-different-heights",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Rolling time of a can down ramps of different heights",
   "researchQuestion": "How does the height h of the top end of a 1.00 m ramp, varied from 5 cm to 25 cm in 5 cm steps, affect the time for a solid metal cylinder to roll down it, and is the result consistent with energy conservation including rotational energy?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Height of the raised end above the bench, 5, 8, 11, 14, 17, 20, 25 cm, each run five times.",
   "dependentVariable": "Time to roll a fixed 1.00 m distance, measured with two light gates or by slow motion video. Calculated: acceleration a = 2s/t², and final speed v.",
   "controlledVariables": "Same cylinder and same ramp surface. Distance travelled fixed at 1.00 m. Release from rest with a ruler held across the top. Ramp checked flat so the cylinder does not drift sideways.",
   "physicsNeeded": "For a solid cylinder, mgh = ½mv² + ½Iω² gives v² = (4/3)gh, and a = (2/3) g sinθ. Plot a (y) against sinθ (x), where sinθ = h/L. The gradient should be 2g/3, about 6.5 m/s², independent of mass.",
   "slVsHl": "SL students can use energy transfer with the fraction of kinetic energy that is rotational and compare the gradient with theory. HL students can derive it with the moment of inertia and compare a solid cylinder with a hollow one.",
   "whereMarksAreLost": "Research design: the question asks about time, which is not linear in h, so no useful graph is planned. Data analysis: uncertainty in h at a shallow ramp not propagated to sinθ. Conclusion: no comparison with the predicted gradient. Evaluation: slipping and ramp flex not considered.",
   "dataNote": "Needs a ramp, metre rule and stopwatch or light gates, and the main uncertainty is starting exactly at rest and timing short runs.",
   "verdict": "Fine as a base but the raw question is too thin. Twist it by comparing a solid and a hollow cylinder, so the moment of inertia gives you a real prediction to test."
  },
  {
   "id": "ball-size-and-rebound-elasticity-on-a-hard-floor",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Ball size and rebound elasticity on a hard floor",
   "researchQuestion": "How does the outer diameter of a solid rubber ball, varied from 20 mm to 60 mm in six steps, change the ratio of rebound speed to impact speed (e = sqrt(h_rebound/h_drop)) after a single bounce from a release height of 1.00 m onto a concrete floor?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Ball diameter: six balls from 20 mm to 60 mm in roughly 8 mm steps, measured with vernier calipers at three orientations and averaged. Ideally the same material for all (for example solid rubber or steel-free bouncy balls from one supplier). 5 drops per ball, 30 drops in total.",
   "dependentVariable": "Rebound height read from a slow motion video (240 fps phone camera) filmed against a metre rule, using the frame where the ball reaches its top. Coefficient of restitution calculated as e = sqrt(h_rebound/h_drop). Optionally, a microphone and audio software can time the gap between the first two impacts to get e from the flight time.",
   "controlledVariables": "Release height fixed at 1.00 m to the bottom of the ball using a clamped release point and a rule with a set square. Same floor surface for every drop, marked with tape. Ball material and temperature kept the same by using balls from one batch stored in the same room. Release without spin by holding the ball between two fingers or using a small clamp.",
   "physicsNeeded": "Conservation of energy before and after impact gives v = sqrt(2gh), so e = v_after/v_before = sqrt(h_rebound/h_drop). Plot e against diameter to test for a trend. Alternatively plot h_rebound against h_drop for one ball, whose gradient is e squared. Also consider mass, since a larger ball of the same material is heavier, and compare the fractional energy lost, 1 - e squared.",
   "slVsHl": "An SL student can find e for each diameter, plot it with error bars and describe the trend and any link to mass. To reach the top band, the student should separate the effect of size from mass and material (for example by comparing a hollow ball and a solid one), analyse the energy lost as sound and heat, and judge whether any trend is larger than the spread of repeats. HL students can add a model of the ball as a nonlinear spring with damping, or examine the contact time.",
   "whereMarksAreLost": "Research design: diameter is confounded with mass, wall thickness and material when different types of ball are mixed, so the comparison is not fair. Data analysis: reading the top of the bounce by eye gives uncertainties of several centimetres, and students often ignore them or propagate them wrongly through the square root. Conclusion: claiming a trend when the differences in e are smaller than the repeat spread. Evaluation: not discussing air resistance, spin, non-vertical bounces, or the fact that the balls are not identical in composition.",
   "dataNote": "Needs vernier calipers, a metre rule and a phone with slow motion video; the main uncertainty is reading the peak height from video frames, plus real variation between balls.",
   "verdict": "A sound and easy investigation, but the topic is common, so it only stands out if the design tackles the confound between size, mass and material. Personalise it by choosing an unusual but consistent ball family, such as sports balls of one material, and by using audio timing as a second measurement of e."
  },
  {
   "id": "ball-speed-at-the-foot-of-a-ramp-against-release-height",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Ball speed at the foot of a ramp against release height",
   "researchQuestion": "How does the release height, varied from 5 cm to 30 cm in 5 cm steps, affect the speed of a steel ball at the bottom of a 1.0 m ramp, and what fraction of gravitational potential energy becomes translational kinetic energy?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Vertical release height from 5 cm to 30 cm, 6 values, with 5 repeats at each.",
   "dependentVariable": "Speed at the bottom from a light gate placed across the ball's diameter (±0.01 m s⁻¹) or from video analysis. Kinetic energy is found from the speed and the mass on a balance.",
   "controlledVariables": "Ball mass and diameter, using one steel ball. Track surface, using the same groove or rail. Release method, letting go without pushing, for instance with a ruler stop. Light gate position, kept at the same point on the track.",
   "physicsNeeded": "For a solid sphere rolling without slipping, mgh = ½mv² + ½Iω² gives v² = (10/7)gh. Plot v² against h, with a gradient of (10/7)g ≈ 14.0 m s⁻². Compare with the value found to find energy lost.",
   "slVsHl": "SL students get the v² against h line and compare the gradient to 10/7 g. Top band work tests the rolling assumption, for example by using a hollow sphere or cylinder to compare moments of inertia. HL students can build the moment of inertia analysis rigorously.",
   "whereMarksAreLost": "Research design: the input says ramp angle is controlled, but changing height at a fixed length changes the angle, so the variables need a clear plan. Data analysis: plotting v against h and missing the square relationship. Conclusion: ignoring rotational energy so that 'lost energy' appears large. Evaluation: not measuring the diameter for the light gate speed.",
   "dataNote": "Needs a ramp, a light gate or a phone camera, and a steel ball. The main uncertainty is the gate's timing over the ball's width and slipping.",
   "verdict": "Easy and widely done, so the interest is in the rolling energy split. Twist: compare a solid ball, a hollow ball and a can to test how mass distribution changes the fraction."
  },
  {
   "id": "bounce-height-and-impact-force-for-cushioning-materials",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Bounce height and impact force for cushioning materials",
   "researchQuestion": "How does the thickness of a foam layer (5, 10, 15, 20, 25, 30 mm) affect the peak deceleration of a 200 g steel ball dropped from 0.50 m onto it?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Foam thickness from 5 mm to 30 mm in six steps, stacking identical 5 mm sheets so the material stays the same. Five drops per thickness.",
   "dependentVariable": "Peak acceleration read from a phone accelerometer taped to the ball holder or a force sensor plate, converted to peak force with F = ma. Optionally rebound height from slow motion video against a ruler.",
   "controlledVariables": "Drop height fixed with a clamp and marked release point. Mass of the falling object fixed by weighing it. Same foam type and density, cut from one sheet. Rigid bench surface under the foam, same for every trial.",
   "physicsNeeded": "Energy transfer mgh to kinetic energy, impulse F·Δt = Δp, and the fraction of energy returned e = h_rebound/h_drop. Plot peak force against 1/thickness, or rebound fraction against thickness. If the deceleration distance d is compressive, F_avg ≈ mgh/d gives a testable link.",
   "slVsHl": "SL students can plot force against thickness and explain with impulse and energy. Top band work compares a model of average force with measured peak force and discusses why they differ. HL students can add a force-time curve integrated to check the impulse equals the momentum change.",
   "whereMarksAreLost": "Research design: comparing 'materials' with no way to hold thickness and density equal. Data analysis: reading the peak from one noisy trace without repeats or uncertainty. Evaluation: ignoring that phone sampling rates can miss the true peak.",
   "dataNote": "Needs a phone accelerometer app or force sensor; the main uncertainty is the sampling rate missing the peak and the ball tilting on impact.",
   "verdict": "Worth choosing if you fix one material and vary thickness, because comparing several unlike materials gives you nothing to linearise. Twist: test the foam from a real helmet or a parcel you own."
  },
  {
   "id": "dc-motor-efficiency-across-a-range-of-lifted-loads",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "SL",
   "title": "DC motor efficiency across a range of lifted loads",
   "researchQuestion": "How does the mass lifted by a small DC motor, varied from 20 g to 200 g in 20 g steps, affect its efficiency at a fixed supply voltage of 3.0 V?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Lifted mass, 20 g to 200 g in steps of 20 g (10 values), each lifted 3 times.",
   "dependentVariable": "Voltmeter and ammeter readings give input power P_in = VI. Metre rule and stopwatch give the time to raise the mass through a fixed height (about 0.80 m), so P_out = mgh/t. Efficiency = P_out/P_in.",
   "controlledVariables": "Supply voltage: stabilised power supply checked with a voltmeter during each lift. Lift height: marked on a rule and the same start and end points used. String and pulley: the same thread and a low-friction pulley throughout. Motor temperature: pause between runs so the motor does not warm up.",
   "physicsNeeded": "Efficiency = useful power out / power in, with P = VI and P = mgh/t. Plot efficiency against lifted mass and find the load at maximum efficiency. A second graph of P_out against m helps show why the curve peaks. Note that current varies during the lift, so read it at steady speed.",
   "slVsHl": "SL: measure, plot the efficiency curve and describe the peak. Top band: model motor losses (resistive heating I²R, friction) and compare the predicted peak with the measured one. HL students can link the back emf of the motor to induction ideas from D.4.",
   "whereMarksAreLost": "Research design: too few masses near the peak, or voltage not held constant. Data analysis: reading current while the motor is accelerating, and no uncertainty on t for short lifts. Conclusion: claiming a rise then fall without comparing to a model. Evaluation: ignoring pulley friction and string stretch.",
   "dataNote": "A cheap hobby motor, two multimeters and a stopwatch are enough; lifts of about 2 s make timing uncertainty large, so use a longer lift height or video timing.",
   "verdict": "Sound and easy to run, and the efficiency peak gives a clear result. Make it yours by explaining the peak with a loss model rather than just plotting it."
  },
  {
   "id": "drop-height-of-water-and-power-from-a-small-turbine",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Drop height of water and power from a small turbine",
   "researchQuestion": "How does the vertical drop height of water (0.20 to 1.00 m in 0.20 m steps) affect the electrical power delivered by a small hobby generator to a fixed resistor?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Drop height of the water outlet above the turbine, 0.20 to 1.00 m, five or six values, 5 repeats each.",
   "dependentVariable": "Voltage across a fixed load resistor with a voltmeter or data logger, giving P = V²/R in W; water flow rate from a measuring cylinder and stopwatch.",
   "controlledVariables": "Volume of water released, using a fixed bucket with a valve; outlet nozzle diameter; load resistance; distance and angle of the jet onto the turbine.",
   "physicsNeeded": "Water gains kinetic energy mgh, so the available power is ρQgh. Plot electrical power against height, expecting a line through the origin. The gradient gives ρQg times efficiency. Compare with the input power to obtain efficiency.",
   "slVsHl": "SL: power against height with efficiency calculated. Top band: note that flow rate also depends on height, and use Bernoulli to correct for it. HL adds nothing essential.",
   "whereMarksAreLost": "Research design: flow rate changes with height and is not controlled. Data analysis: only peak voltage is read from a fluctuating signal. Evaluation: splash losses and turbine friction not discussed.",
   "dataNote": "Needs a hobby DC motor as generator, a tube, a logger; the main uncertainty is the fluctuating output, so record V against time and average.",
   "verdict": "A solid energy conversion project if efficiency is the focus. Test a second turbine design to make it your own."
  },
  {
   "id": "efficiency-of-a-pulley-system-when-lifting-loads",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Efficiency of a pulley system when lifting loads",
   "researchQuestion": "How does the efficiency of a two-pulley block and tackle change as the load is increased from 0.20 kg to 1.00 kg in steps of 0.20 kg, when lifted through 0.30 m?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Load lifted: 5 to 6 values from 0.20 to 1.00 kg, each lift repeated 3 times, with an optional second series with different numbers of supporting strings.",
   "dependentVariable": "Effort measured with a force sensor or newton meter as the load rises slowly, and distances moved by the load and by the effort measured with a rule; work input is F_effort times the effort distance, work output is mgh, and efficiency is output divided by input.",
   "controlledVariables": "Lifting height: fixed at 0.30 m with markers. Lifting speed: slow and steady, timed to about 0.05 m/s. Pulleys and string: same set and lubrication. Number of supporting strings: kept the same for the load series.",
   "physicsNeeded": "Work W = F s, useful work mgh, efficiency = (mgh) / (F_effort s). Plot work output against work input; the gradient is efficiency. The energy lost by friction and pulley weight explains the shortfall from 100 percent.",
   "slVsHl": "SL students find efficiency for each load and describe the trend. Stronger work models the constant friction plus the pulley weight, and predicts why efficiency rises with load towards a limit.",
   "whereMarksAreLost": "Research design: only measuring force on a stationary load, missing friction. Data analysis: reading a bouncing newton meter. Evaluation: not linking energy loss to friction and the weight of the moving pulley.",
   "dataNote": "Pulleys, string, masses and a force sensor; the main uncertainty is jerky force reading while the load moves.",
   "verdict": "A decent choice if you focus on efficiency, since simple work done equals mgh is not really a question. The rise of efficiency with load is a good personal finding."
  },
  {
   "id": "efficiency-of-a-small-dc-motor-lifting-a-load",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Efficiency of a small DC motor lifting a load",
   "researchQuestion": "How does the electrical input power, varied from 0.5 to 3.0 W by changing supply voltage, affect the efficiency of a small DC motor lifting a 50 g mass?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Supply voltage to the motor, 1.0 to 6.0 V in steps of 1.0 V (six values), three trials each. Input power found from voltage times current.",
   "dependentVariable": "Efficiency = useful output power divided by input power. Output power = mgh/t, using a stopwatch or video for the time to lift the mass through a measured height with a metre rule. Voltage and current from two multimeters.",
   "controlledVariables": "Lifted mass: 50 g throughout. Lift height: fixed at 0.80 m. Motor and string: the same motor with the same spool. Motor temperature: rest between runs so resistance stays similar.",
   "physicsNeeded": "Efficiency = mgh/(VIt). Energy losses come from Joule heating I²R in the windings and friction. Plot efficiency against input power, and also plot output power against input power. A model of P_out = P_in minus I²R minus friction can be tested.",
   "slVsHl": "SL: measure and plot efficiency, discuss losses qualitatively. Top band: estimate winding resistance from a stalled test and fit a loss model quantitatively. HL: link to back emf in the motor, if induction is covered.",
   "whereMarksAreLost": "Research design: no clear method for output power, or lifting speed not constant. Data analysis: uncertainty in short lift times ignored. Evaluation: not commenting on the mass being too small for the higher voltages, which pushes efficiency down.",
   "dataNote": "Two multimeters, a motor, a pulley and a stopwatch are enough; the main uncertainty is the lift time at high voltage, so use video timing.",
   "verdict": "A solid, safe choice with clear energy conversions. Make it your own by extracting the winding resistance and testing whether it explains the losses."
  },
  {
   "id": "energy-lost-by-a-trolley-on-different-ramp-surfaces",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "SL",
   "title": "Energy lost by a trolley on different ramp surfaces",
   "researchQuestion": "How does the surface material of a 1.00 m ramp inclined at 15° (sandpaper, carpet, plastic, wood, felt, foil: 6 values) affect the percentage of gravitational potential energy converted to kinetic energy at the base?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Ramp surface material, 6 types glued on the same board. Each tested 5 times.",
   "dependentVariable": "Speed at the bottom from a light gate with a card of known width. Kinetic energy ½mv² is compared with mgΔh, and the fraction dissipated is 1 − KE/PE.",
   "controlledVariables": "Ramp angle: set with the same height blocks and checked with a protractor. Trolley mass: measured on a balance. Release position: from the same mark with no push. Wheels: same trolley, or a sliding block with the same contact area.",
   "physicsNeeded": "Energy conservation: mgh = ½mv² + work against friction. Then fraction lost = 1 − v²/(2gh). With a sliding block, work against friction is μmg cosθ × d, giving μ. Plot v² against distance down the slope for each material; the gradient gives the acceleration and thus μ.",
   "slVsHl": "SL students can compare fractions and connect them to friction. To reach the top band, extract μ from the gradient of v² against distance and discuss rotational KE for the wheels. HL depth is less natural here.",
   "whereMarksAreLost": "Research design: only one release distance, so no trend is available. Data analysis: rolling wheel energy is ignored when the trolley is said to lose energy. Evaluation: surface wear and dust between repeats.",
   "dataNote": "A ramp, a light gate and a balance are enough; the main uncertainty is the speed from a light gate and the ramp angle.",
   "verdict": "Fine, but the IV is categorical, which limits the analysis. Twist it by using several release distances per surface and finding μ from graphs."
  },
  {
   "id": "energy-lost-when-a-pendulum-bob-strikes-a-wall",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Energy lost when a pendulum bob strikes a wall",
   "researchQuestion": "How does the mass of a steel ball, from 10 g to 60 g in 5 steps, affect the fraction of kinetic energy lost when it swings from a fixed release height into a rigid block?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Ball mass, 5 to 6 values (steel or brass spheres of the same radius are not possible, so use drilled or different material balls and record diameter), 5 repeats each.",
   "dependentVariable": "Release height and rebound height read from a video frame against a ruler, with the tracker software. Fraction lost = 1 − h_rebound/h_release, with propagated uncertainty.",
   "controlledVariables": "Release height (fixed with a clamp stop). String length and type. Wall material and its rigidity (clamped steel block). Ball diameter, or note its change and its effect on air drag.",
   "physicsNeeded": "Gravitational potential energy mgh converts to kinetic energy and back. Fraction lost = 1 − h2/h1. Plot fraction lost against mass; if the collision is independent of mass the gradient is zero, which is a testable prediction.",
   "slVsHl": "SL: measure and compare with a flat line. Top band: relate the result to the coefficient of restitution e = √(h2/h1), and consider air drag and string losses separately.",
   "whereMarksAreLost": "Research design: masses that also change diameter, so more than one variable is changing. Data analysis: reading rebound heights from a video with large uncertainty. Conclusion: claiming a trend when values overlap within error bars.",
   "dataNote": "Needs a phone camera at 120 fps or more; reading the rebound height is the main uncertainty.",
   "verdict": "A decent idea if you expect and test a null result. Vary the wall material as well to make it your own."
  },
  {
   "id": "paddle-area-of-a-small-waterwheel-and-its-efficiency",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Paddle area of a small waterwheel and its efficiency",
   "researchQuestion": "How does the paddle area of a hand built waterwheel, from 4 cm² to 20 cm² in 5 steps, affect its efficiency in lifting a 50 g mass or turning a small motor as generator, at a fixed water flow rate?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Paddle area, 5 values (card or plastic cut to 4, 8, 12, 16, 20 cm²), 3 or more repeats each.",
   "dependentVariable": "Electrical output power from a small DC motor used as a generator, P = V²/R, with a voltmeter across a load resistor. Input power from water flow rate (measuring cylinder and stopwatch) and drop height, P = ρQgh. Efficiency = P_out/P_in.",
   "controlledVariables": "Water flow rate (constant head tank with a fixed tap). Drop height. Number of paddles and the wheel radius. Load resistor value.",
   "physicsNeeded": "Input power P = ρQgh; output power P = V²/R. Efficiency = P_out/P_in. Plot efficiency against paddle area and find where the curve peaks, then explain with momentum transfer from the water.",
   "slVsHl": "SL: collect and plot the data, and comment on the trend. Stronger: explain the peak with a momentum model of the jet hitting the paddle, and account for splash losses and friction.",
   "whereMarksAreLost": "Research design: flow rate not held constant, and too few areas. Data analysis: not propagating uncertainty into efficiency. Evaluation: not measuring friction or splash losses.",
   "dataNote": "Needs a motor, a voltmeter and a steady water supply; the flow rate stability and generator efficiency are the main uncertainties.",
   "verdict": "Messy but personal, and it can score if you keep the flow rate under control. Build your own wheel and measure output at several load resistances to find the best."
  },
  {
   "id": "peak-lifting-speed-of-a-hand-held-load-against-mass",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Peak lifting speed of a hand-held load against mass",
   "researchQuestion": "How does the mean speed of lifting a load through 0.50 m vary as the mass is increased from 1.0 kg to 6.0 kg in 1.0 kg steps?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Lifted mass: 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0 kg (6 values), using slotted masses on a hanger, 5 repeats each with rests between.",
   "dependentVariable": "Time to raise the load through a marked 0.50 m, taken from a video recorded at 120 frames per second or a ultrasonic motion sensor. Mean speed = 0.50 m divided by time; power = mgv.",
   "controlledVariables": "Lifting distance: fixed with tape marks at 0.50 m. Person: one participant, with a warm-up. Technique: same posture, elbow starting angle and instruction to lift as fast as possible. Rest time: 2 minutes between lifts to avoid fatigue.",
   "physicsNeeded": "Muscle force-velocity behaviour is usually modelled by the Hill relation, and mechanical power is P = mgv. Plot v (y) against mass m (x) to see the curve, and P against m to find the peak power. A straight line of 1/v against m is a simple test of a linear model.",
   "slVsHl": "SL students plot v against m and calculate power and work. Stronger work compares the curve with a simple model and separates constant-speed from accelerating phases. The original heavier-is-slower claim is obvious, so the quantitative shape is the point.",
   "whereMarksAreLost": "Research design: human participant, fatigue and ethics are not controlled or discussed. Data analysis: stopwatch timing with reaction error of about 0.2 s on a lift of under 1 s. Evaluation: not commenting on the acceleration phase.",
   "dataNote": "Needs a phone camera or motion sensor and slotted masses; the main uncertainty is timing a short lift and one person's fatigue.",
   "verdict": "Fine if you replace the stopwatch with video and go for peak power. Get teacher approval for the human-participant risk."
  },
  {
   "id": "power-from-a-model-wind-turbine-at-different-blade-lengths",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Power from a model wind turbine at different blade lengths",
   "researchQuestion": "How does the electrical power delivered by a model turbine to a fixed 10 ohm load change when the blade length is varied from 6 cm to 16 cm in steps of 2 cm?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Blade length: 6, 8, 10, 12, 14 and 16 cm (6 values), with 3 or more repeats each. Blades are cut from the same card or plastic sheet and trimmed.",
   "dependentVariable": "Voltage across a fixed load resistor measured with a voltmeter or logger, giving P = V²/R. Wind speed at the rotor is checked with an anemometer.",
   "controlledVariables": "Wind speed: same fan setting and distance, checked at the rotor with an anemometer. Blade number, pitch angle and width: use a template and a protractor. Load resistance: same resistor. Generator: same small DC motor used as a generator.",
   "physicsNeeded": "Power in the wind through the swept area is P = ½ρAv³ with A = πL², so power should be proportional to L² if efficiency is constant. Plot P (y) against L² (x); gradient = ½ρπv³ × efficiency, so efficiency can be estimated. A non-linear plot shows tip losses or a stalled rotor.",
   "slVsHl": "SL students test P against L² and find the efficiency. HL or top band work also examines the non-uniform wind profile from a fan, and compares the power coefficient with the Betz limit of 59 percent.",
   "whereMarksAreLost": "Research design: fan wind is not uniform across large blades, so the wind speed is not truly controlled. Data analysis: ignoring that power is not simply V×I of a loaded motor. Evaluation: not commenting on friction in the generator or turbulence.",
   "dataNote": "Needs a fan, a small DC motor and an anemometer; the main uncertainty is the uneven airflow across the rotor.",
   "verdict": "Fine and practical, but common as a theme. Make it personal by measuring the wind speed map across the fan face and deriving efficiency rather than just plotting power."
  },
  {
   "id": "ramp-angle-and-the-run-out-distance-of-a-rolling-ball",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Ramp angle and the run-out distance of a rolling ball",
   "researchQuestion": "How does ramp angle from 5 to 35 degrees affect the distance a steel ball rolls on a flat wooden track after it leaves a ramp with a release length of 0.50 m?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Ramp angle, 7 values from 5 to 35 degrees in 5 degree steps, set by a fixed release length and adjusted height, 5 runs each.",
   "dependentVariable": "Run-out distance on the flat track from the base of the ramp, measured with a tape and marked by a small tab. Speed at the base from a light gate or video analysis to see the energy conversion.",
   "controlledVariables": "Same ball, same release length along the ramp so that it starts at the same point. Ramp surface and flat track kept the same and cleaned. A smooth transition curve at the ramp base. Ball released without push, by a ruler held at the top.",
   "physicsNeeded": "For a rolling ball, mgh = 1/2 m v^2 + 1/2 I w^2 (for a solid sphere, v^2 = (10/7) g h). Constant deceleration on the flat gives d = v^2 / (2a). Plot d (y) against sin(theta) (x) with h = L sin(theta): expect a straight line through the origin.",
   "slVsHl": "SL students plot d against sin(theta) and comment on the trend. Better work extracts the deceleration on the flat track and compares v from the light gate with (10/7) g h. HL depth can treat rotational kinetic energy and rolling resistance.",
   "whereMarksAreLost": "Research design: kink at the ramp base, so the ball bounces and loses energy. Data analysis: plotting distance against angle rather than sin(theta) and assuming linear. Conclusion: claiming a trend without a physical reason from the energy split.",
   "dataNote": "Needs a ramp, ball, tape and optionally a light gate or phone video; main uncertainty is the base transition and the point where the ball stops.",
   "verdict": "Easy to run and easy to make trivial. It becomes solid work if you linearise with sin(theta) and check the rolling energy split against the measured speeds."
  },
  {
   "id": "rebound-efficiency-of-a-ball-on-different-surfaces",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Rebound efficiency of a ball on different surfaces",
   "researchQuestion": "How does the fraction of gravitational potential energy retained after one bounce of a tennis ball change with drop height from 0.20 m to 1.20 m in steps of 0.20 m, on a hard laboratory floor?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Drop height h0 from 0.20 to 1.20 m in steps of 0.20 m (6 values), with 5 drops at each height. A second run could repeat this on a different surface.",
   "dependentVariable": "Rebound height h1 read from slow motion video (120 fps or more) filmed against a metre rule, using a phone. Efficiency is calculated as h1/h0, since mass cancels in mgh1/mgh0.",
   "controlledVariables": "Same ball, checked with a balance before and after. Same surface, taped down and level. Release with no spin, using a clamp or a marked release point. Ball temperature and room temperature kept steady, with drops in one session so the ball does not warm up.",
   "physicsNeeded": "Gravitational potential energy Ep = mgh, with efficiency = Ep(after)/Ep(before) = h1/h0. Plot h1 against h0. The gradient is the efficiency, or the square of the coefficient of restitution. A straight line through the origin supports a constant fraction. Curvature would suggest speed dependent losses. Comparing with muscle efficiency of about 25 % is a side comment, not the core of the investigation.",
   "slVsHl": "SL students give a clear h1 against h0 graph with the gradient and uncertainty. To reach top band, link efficiency to the coefficient of restitution e = sqrt(h1/h0), explain where the energy goes (sound, heat, deformation), and test a second surface or ball. HL students can add the time between successive bounces and check consistency with a geometric series of rebound heights.",
   "whereMarksAreLost": "Research design: the original muscle comparison is not measurable with balls, so the question must stay on the bounce itself. Data analysis: reading the rebound height by eye gives large uncertainty, so use video and propagate it. Conclusion: claiming a constant efficiency without checking the fit residuals. Evaluation: ignoring parallax on the ruler and air resistance at large heights.",
   "dataNote": "Needs a metre rule, a ball and a phone with slow motion. The main uncertainty is reading the peak of the rebound from video frames, about ±1 cm.",
   "verdict": "Simple and cheap, and easy to do well, but examiners have seen bouncing balls. Drop the muscle comparison and add a twist, for example your own sport ball or a surface such as a gym mat. This is a measurable version, but it is not a biological study."
  },
  {
   "id": "rebound-energy-loss-of-a-ball-on-different-floor-materials",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Rebound energy loss of a ball on different floor materials",
   "researchQuestion": "How does the type of flat surface (glass, wood, rubber mat, carpet tile, cork, concrete slab; 6 materials) affect the coefficient of restitution e of a squash ball dropped from 1.00 m, found from rebound height using e = √(h/H)?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Surface material, 6 different flat samples of similar thickness, all laid on the same rigid floor. A second run can vary drop height (0.40 to 1.60 m in 5 steps) on one material to test whether e depends on impact speed.",
   "dependentVariable": "Rebound height h after the first bounce, read from a video recorded at 120 fps or more beside a fixed metre rule, measured to ±0.5 cm. e is calculated as √(h/H) for each drop. 5 repeat drops per material give a mean and a spread.",
   "controlledVariables": "Same ball, kept at room temperature and checked for pressure or wear, so ball properties do not drift. Release height fixed with a clamp and a release method that gives no spin, such as a light suction or a two-finger release. Camera position and distance fixed, with the ruler in the same plane as the ball to limit parallax. Sample resting on the same solid base, so the base does not absorb energy differently.",
   "physicsNeeded": "Energy before and after impact: v = √(2gH) on arrival and √(2gh) on leaving, so e = v_out/v_in = √(h/H). Plot h against H for one surface: the gradient equals e², so e = √gradient. For the material comparison, a bar chart of mean e with error bars. Extension: e against impact speed to see if e is constant, and energy lost as a fraction 1 − e².",
   "slVsHl": "SL students can compare materials with a clear method, uncertainties and a bar chart of e. Top band work uses the h against H gradient to get e for each material, propagates uncertainty properly and discusses why e may vary with speed. HL depth can come from modelling the contact as a damped spring, or from using contact time or sound to estimate energy going into vibration and heat.",
   "whereMarksAreLost": "Research design: listing materials without saying why they differ, and not controlling spin or release. Data analysis: using one drop per material, or reporting e without an uncertainty from the h readings and the square root. Conclusion: claiming a ranking when the error bars overlap. Evaluation: ignoring that thin samples on a floor behave as a layered system, and that parallax and frame rate limit the height reading.",
   "dataNote": "Needs a ball, metre rule, phone camera with slow motion and clamp stand; the main uncertainty is reading the peak height from video, about ±1 cm.",
   "verdict": "A safe, doable idea but very common, so it only scores well with a proper h against H gradient and honest uncertainties. Personalise it by choosing materials from your own home or school, such as a gym mat or a sports court sample, and by testing the speed dependence."
  },
  {
   "id": "rebound-height-of-a-ball-which-factor-matters",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Rebound height of a ball: which factor matters",
   "researchQuestion": "How does the drop height of a tennis ball (0.20 to 1.20 m in 6 steps) affect its coefficient of restitution on a concrete floor?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Drop height from 0.20 to 1.20 m, 6 values, each repeated 5 times. Choose one factor only; the others below stay constant.",
   "dependentVariable": "Rebound height measured from 240 fps video beside a metre rule. Coefficient of restitution e = √(h_rebound/h_drop), or the speeds either side of the bounce from a microphone or Tracker.",
   "controlledVariables": "Surface: same floor tile throughout. Ball: same ball, kept at room temperature (checked with a thermometer). Inflation: sealed ball, not changed between runs. Release: from rest by hand, checked on video for spin.",
   "physicsNeeded": "Speed just before impact is v = √(2gh) and after is √(2gh'), so e = √(h'/h). Plot h' against h; the gradient is e². A non-linear graph would show that e depends on speed. Energy lost per bounce is mg(h − h').",
   "slVsHl": "SL students can plot h' against h and interpret the gradient. To reach the top band, compare several bounces on one drop and discuss deformation and air drag. HL students may use a model of the ball as a damped spring.",
   "whereMarksAreLost": "Research design: several variables are changed together so no conclusion is possible. Data analysis: rebound height is read by eye with large uncertainty. Evaluation: ignores parallax and the ball's spin.",
   "dataNote": "A ball, a metre rule and a phone camera are enough; the main uncertainty is reading the rebound peak.",
   "verdict": "Very common as an idea, so it needs a twist. Try temperature of a squash ball (5 to 60 °C in a water bath) to make it your own."
  },
  {
   "id": "stored-energy-in-springs-of-different-stiffness-and-construction",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Stored energy in springs of different stiffness and construction",
   "researchQuestion": "How does the spring constant k of five helical steel springs (k about 5 to 60 N/m) affect the elastic energy stored, found from the area under the force-extension graph, when each is stretched to a fixed extension of 0.100 m?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Spring identity, five to six springs of different stiffness (different wire diameter or coil number), each characterised by its own k. Alternatively vary the number of identical springs in series or parallel, giving 5+ effective values of k.",
   "dependentVariable": "Extension measured with a metre rule (or a marker and camera) for at least six hanging masses per spring, three repeats each. Force from mg. Stored energy from the area under the F-x graph and compared with ½kx².",
   "controlledVariables": "Final extension fixed at 0.100 m using a marked stop position. Stay within the elastic limit by checking the spring returns to its original length. Same rule and reading height to limit parallax. Mass values from one balance.",
   "physicsNeeded": "F = kx and E = ½kx². Plot F against x for each spring, gradient is k. Then plot E against k for the fixed extension, which should be a straight line through the origin with gradient ½x².",
   "slVsHl": "SL students find k for each spring and compare ½kx² with the graph area. Top band work tests the linearity limit, compares series and parallel prediction of k, and estimates energy lost when a spring is released and oscillates.",
   "whereMarksAreLost": "Research design: the original question is vague about 'spring type', so define exactly what changes. Data analysis: forgetting uncertainty in gradient and propagation to E. Conclusion: not comparing stored energy with the prediction. Evaluation: ignoring spring mass and hysteresis.",
   "dataNote": "Springs, slotted masses, hanger and metre rule are enough; the main uncertainty is reading the extension to about 1 mm.",
   "verdict": "Sound and easy, but basic unless you add series and parallel prediction or hysteresis. Pick it if you want a clean, well-controlled dataset, and add a loading-unloading loop to make it yours."
  },
  {
   "id": "water-drop-release-height-and-rebound-from-a-water-surface",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Water drop release height and rebound from a water surface",
   "researchQuestion": "How does the release height of a 50 microlitre water drop (10 to 60 cm, 6 heights) affect the height of the small secondary droplet that jumps up from a water surface?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Release height of the drop measured from the surface, 10 to 60 cm in 10 cm steps, 5 drops per height, delivered by a burette or syringe with a fixed tip.",
   "dependentVariable": "Rebound height of the droplet read from high-speed video (slow-motion phone, 240 fps) against a ruler in the frame. Impact speed calculated from height, and the ratio of rebound to fall height found.",
   "controlledVariables": "Drop size, by using the same tip and counting the mass of 20 drops. Depth and width of the water tray. Lighting and camera position, fixed with a clamp. Water temperature and any surface film or dust, by using fresh water each set.",
   "physicsNeeded": "Impact speed v = sqrt(2 g h), so kinetic energy at impact is proportional to h. Plot rebound height against fall height and see if the line is straight; the gradient gives the efficiency of energy return. Consider surface tension energy of the droplets formed.",
   "slVsHl": "SL: rebound versus fall height graph and an energy efficiency estimate. Top band: compare with surface energy 4 pi r^2 sigma and explain why the rebound is not a single simple bounce and may only occur in a limited height range. HL adds nothing needed.",
   "whereMarksAreLost": "Research design: not stating how the rebound is defined. Data analysis: reading a fast event by eye with no video. Conclusion: claiming energy conservation when the result shows a small fraction returned. Evaluation: the rebound only appears at certain heights, and scatter is large.",
   "dataNote": "Needs slow-motion video and good lighting; the main uncertainty is the small secondary droplet, which is irregular and may not occur at every height.",
   "verdict": "Interesting but risky because rebound can be rare and scattered. Choose it only if you have slow-motion video; a safer twist is measuring the crater or splash height instead."
  },
  {
   "id": "where-a-rubber-cord-stops-obeying-hooke-s-law",
   "topic": "A.3",
   "topicName": "Work, energy and power",
   "level": "both",
   "title": "Where a rubber cord stops obeying Hooke's law",
   "researchQuestion": "How does the elastic energy stored in a rubber cord differ from the value predicted by Hooke's law as the extension increases from 2 cm to 30 cm in 2 cm steps?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Extension of a rubber cord or elastic band, 2 cm to 30 cm in 2 cm steps (15 values), during loading and again during unloading.",
   "dependentVariable": "Force from a force sensor or a set of slotted masses, extension from a fixed metre rule. Stored energy is found from the area under the force against extension graph by the trapezium rule, then compared with ½kx² using the initial gradient.",
   "controlledVariables": "Cord sample: the same piece and original length for every run. Temperature: room conditions, and rest between cycles to limit hysteresis. Rate of loading: slow, steady steps with a fixed 10 s wait before each reading. Zero position: the unstretched length is checked before each run.",
   "physicsNeeded": "Hooke's law F = kx and elastic energy E = ½kx² = area under the F-x graph. Plot F against x and compare with the straight-line extrapolation. The difference between loading and unloading areas is the energy dissipated as thermal energy.",
   "slVsHl": "SL: plot F-x, find the limit of proportionality and compare energies. Top band: quantify the hysteresis loop and relate it to energy lost, with a proper uncertainty on the area. HL adds nothing syllabus-wise but can use a fitted non-linear model.",
   "whereMarksAreLost": "Research design: a steel spring is chosen, which stays linear over the range, so there is nothing to investigate. Data analysis: area from crude graph counting with no uncertainty. Conclusion: an unsupported limit value. Evaluation: not commenting on time dependence (creep) of rubber.",
   "dataNote": "Slotted masses, a rule and a stand are enough; the main uncertainty is creep, so readings drift with waiting time.",
   "verdict": "Good if you use rubber, where the physics is interesting. Personalise it by comparing two different cords or a band and a spring."
  },
  {
   "id": "angular-acceleration-of-a-pulley-driven-wheel-against-torque",
   "topic": "A.4",
   "topicName": "Rigid body mechanics",
   "level": "HL",
   "title": "Angular acceleration of a pulley-driven wheel against torque",
   "researchQuestion": "How does the torque applied to a bicycle wheel, varied by hanging masses from 20 g to 120 g on a string wound round its axle, affect its angular acceleration?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Hanging mass (20 g to 120 g in 20 g steps, 6 values, three drops each), which sets the tension and hence the torque about the axle.",
   "dependentVariable": "Time for the mass to fall a fixed height of about 1.0 m, measured with a phone at 240 fps or light gates. From this the linear acceleration a is found, and angular acceleration α = a/r.",
   "controlledVariables": "Moment of inertia of the wheel: same wheel, no added masses. Axle radius: measured with vernier calipers. Fall height: fixed with a marked scale. Friction at the bearing: wheel spun and checked before each run, the same bearing used throughout.",
   "physicsNeeded": "τ = Iα, with τ = T r and T = m(g − a). Plot τ (y) against α (x): the gradient is the moment of inertia I and the intercept is the frictional torque. HL only, as rotational dynamics is in A.4.",
   "slVsHl": "Needs HL content. At HL, get I from the gradient and compare it with a value from the wheel's mass and radius or from a second method such as a swing. Top band: use the intercept for the bearing friction and justify using T = m(g − a) instead of T = mg.",
   "whereMarksAreLost": "Research design: the input idea is about force types in general and not measurable, so students who keep it vague get no clear IV. Data analysis: using T = mg, which overestimates torque at large masses. Conclusion: not comparing I with an independent estimate. Evaluation: ignoring string thickness and slipping of the string on the axle.",
   "dataNote": "Needs a wheel or turntable on a good axle, string, masses and a timing method; the main uncertainty is the fall time and the bearing friction.",
   "verdict": "The original is far too broad, so I have cut it to one clean torque against α test, which is much better. Good for HL students who want mechanics with a real intercept meaning; not suitable for SL."
  },
  {
   "id": "angular-speed-change-when-masses-move-inward",
   "topic": "A.4",
   "topicName": "Rigid body mechanics",
   "level": "HL",
   "title": "Angular speed change when masses move inward",
   "researchQuestion": "How does the starting radius of two 200 g masses on a freely rotating stool, varied from 20 cm to 60 cm, affect the ratio of final to initial angular speed after they are pulled in to 10 cm?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Starting radius of the masses, 20 cm to 60 cm in 10 cm steps (5 values or more, 3 repeats each).",
   "dependentVariable": "Angular speed before and after pulling the masses in, from slow motion video with a marked pointer and frame counting. The ratio ω_f/ω_i is calculated and compared with I_i/I_f.",
   "controlledVariables": "Bearing friction: a well oiled turntable and short time between measurements. Final radius: fixed with a stop at 10 cm. Masses: the same pair each time. Starting push: a consistent small initial spin so angular speeds are similar.",
   "physicsNeeded": "Conservation of angular momentum L = Iω when net external torque is negligible. Plot ω_f/ω_i against I_i/I_f (calculated from mr²), and expect a line of gradient 1. The apparatus's own moment of inertia adds a constant to each I.",
   "slVsHl": "This is HL content. Top band work measures the apparatus's own moment of inertia and shows how it changes the predicted ratio, and estimates the angular momentum lost to friction.",
   "whereMarksAreLost": "Research design: masses moved unevenly so the axis shifts. Data analysis: reading angular speed by eye instead of from video. Conclusion: not accounting for the moment of inertia of the rotating platform. Evaluation: ignoring friction and the frame rate limit on ω precision.",
   "dataNote": "A bicycle wheel or a rotating stool with a phone camera at 120 fps works; the main uncertainty is friction and uneven pulling in.",
   "verdict": "A vivid demonstration and worth doing if you have a good bearing. The apparatus inertia correction is what turns it into a strong IA."
  },
  {
   "id": "mass-distribution-and-speed-of-rolling-cylinders-on-a-ramp",
   "topic": "A.4",
   "topicName": "Rigid body mechanics",
   "level": "HL",
   "title": "Mass distribution and speed of rolling cylinders on a ramp",
   "researchQuestion": "How does the moment of inertia factor k (I = k m r^2, from 0.4 to 1.0 across 6 objects) affect the speed at the bottom of a 1.0 m ramp at 10 degrees?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Rolling objects of the same radius but different mass distributions: solid cylinder, hollow tube, cylinders filled with sand, water, or with added rings of mass. 6 configurations, 5 runs each. k calculated from the geometry and mass.",
   "dependentVariable": "Speed at the bottom from two light gates a short distance apart with a card of known width, or from the time down the ramp with video. v is calculated from distance and time and compared with the theoretical value.",
   "controlledVariables": "Ramp angle, by measuring height and length with a metre rule. Release point, a stop at the same line each time. Ramp surface, the same board with no slipping. Radius, checked with a calliper for every object.",
   "physicsNeeded": "Energy conservation: m g h = 1/2 m v^2 + 1/2 I omega^2, with v = omega r, so v^2 = 2 g h / (1 + k). Plot v^2 against 1 / (1 + k); the gradient is 2 g h, which can be compared with the measured value.",
   "slVsHl": "Rotational dynamics is HL only. At HL, take the graph to a value of g with uncertainty. Top band: study the effect of slipping, rolling resistance, and the difference between energy loss and the idealised model.",
   "whereMarksAreLost": "Research design: varying mass and radius together with the distribution. Data analysis: assuming k for filled objects without calculation. Evaluation: ignoring that the objects may slip or that the light gate measures speed of a section rather than centre of mass.",
   "dataNote": "Needs light gates or good video and rollers with known geometry; the main uncertainty is calculating k for partially filled cylinders and rolling friction.",
   "verdict": "A strong HL option if the graph is linearised properly and k is computed rather than guessed. The twist is to predict v for a new object before testing it."
  },
  {
   "id": "moment-of-inertia-by-torque-from-a-falling-mass",
   "topic": "A.4",
   "topicName": "Rigid body mechanics",
   "level": "HL",
   "title": "Moment of inertia by torque from a falling mass",
   "researchQuestion": "How does the distance of two 100 g masses from the axis, varied from 5 cm to 25 cm in 4 cm steps, affect the moment of inertia of a turntable arm measured by angular acceleration?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Radial distance r of two equal masses on a horizontal rod, 5 cm to 25 cm in 5 steps or more (6 values, 3 repeats).",
   "dependentVariable": "A hanging mass on a string wound round the axle gives the torque. Fall time over a measured height, with a stopwatch or video, gives the linear acceleration a, then α = a/R. Moment of inertia I = τ/α, with τ = mR(g − a).",
   "controlledVariables": "Driving torque: the same hanging mass and axle radius R. Total mass on the rod: masses added symmetrically and never changed. Axle friction: measure it in a run with no added masses and subtract it. Fall height: fixed and measured each time.",
   "physicsNeeded": "τ = Iα and I = Σmr². Plot I against r², the gradient gives the sum of the masses and the intercept gives the apparatus's own moment of inertia. Compare the gradient with 2m = 0.200 kg.",
   "slVsHl": "Rigid body dynamics is HL only, so this is an HL topic. Depth comes from the intercept analysis, the friction correction and treating the point mass approximation critically for finite sized masses.",
   "whereMarksAreLost": "Research design: no way to separate frictional torque. Data analysis: assuming a = g/2 style shortcuts or ignoring string tension. Conclusion: not comparing the gradient with the known mass. Evaluation: not commenting on masses having their own size.",
   "dataNote": "A retort stand axle or a low-friction turntable with string, pulley and stopwatch works; short fall times limit precision, so use video analysis.",
   "verdict": "Excellent HL idea with a clean linearisation and a built-in check on the gradient. Add your own friction calibration to make it stand out."
  },
  {
   "id": "moment-of-inertia-of-a-wheel-with-movable-masses",
   "topic": "A.4",
   "topicName": "Rigid body mechanics",
   "level": "HL",
   "title": "Moment of inertia of a wheel with movable masses",
   "researchQuestion": "How does the radius r of four 50 g masses clamped on a bicycle-style wheel (r = 0.05 to 0.25 m in 5 steps) affect its angular acceleration when a 100 g hanging mass drives it through a string wound on the axle?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Radial position r of four equal masses on the wheel spokes or rim slots, 0.05, 0.10, 0.15, 0.20, 0.25 m, each run 5 times.",
   "dependentVariable": "Angular acceleration α, found from a video (phone at 120 fps, Tracker) of the falling mass: a from a straight-line fit of distance against t squared, then α = a / axle radius. Moment of inertia then calculated from I = T·R/α.",
   "controlledVariables": "Driving torque: same hanging mass and same axle radius, checked with a ruler and balance. Total mass on the wheel: same four masses every run. Friction: same axle, tested with no added mass and included as an intercept. Release height: fixed by a marked start line.",
   "physicsNeeded": "τ = Iα with I = I0 + Σ m r². Plot I (or 1/α) against r². The gradient gives the total added mass 4m, which can be checked against the balance, and the intercept gives I0 of the bare wheel. Tension in the string is T = m(g − a), not mg.",
   "slVsHl": "Rotational dynamics is HL only, so an SL student would need to avoid this or reframe it as energy conservation with a falling mass. At HL, top band work compares the gradient with 4m, deals with axle friction and tension correctly, and tests the parallel axis contribution of masses that are not point-like.",
   "whereMarksAreLost": "Research design: torque assumed to equal mg times the axle radius, ignoring that the string tension is lower. Data analysis: friction ignored, leading to a nonzero intercept that is never explained. Conclusion: no comparison of the gradient with the measured masses. Evaluation: uncertainty in release timing not linked to the spread of α.",
   "dataNote": "Needs a wheel or turntable on a low friction axle, clamps, a phone camera and Tracker; friction in the bearing is the main uncertainty.",
   "verdict": "Good for an HL student who wants real rotational physics with a clean check against the balance. The twist is to build the wheel from something at home, such as a bicycle wheel, and to measure its own bearing friction."
  },
  {
   "id": "racing-rolling-objects-down-the-same-ramp",
   "topic": "A.4",
   "topicName": "Rigid body mechanics",
   "level": "HL",
   "title": "Racing rolling objects down the same ramp",
   "researchQuestion": "How does the shape factor k = I/(mr²) of five rolling objects affect their acceleration down a 15° ramp of length 1.20 m?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Object type, giving different k: solid sphere (0.4), solid cylinder (0.5), thin hollow cylinder (1.0), hollow sphere (0.67) and a cylinder with added mass at its rim, five or more values with 5 repeats each.",
   "dependentVariable": "Time to travel down a marked 1.20 m with a stopwatch or light gates, giving a = 2s/t². This is compared with the predicted a = g sin θ / (1 + k).",
   "controlledVariables": "Ramp angle: set from height and length and checked with a protractor. Surface: the same track, so slipping does not happen. Release: from rest at the same mark with a stopper. Ramp length: fixed and measured.",
   "physicsNeeded": "Energy conservation with rotation: mgh = ½mv² + ½Iω² gives a = g sin θ / (1 + k). Plot a against 1/(1+k), the gradient is g sin θ. Mass and radius cancel, which can be tested directly.",
   "slVsHl": "Rotational kinetic energy belongs to HL rigid body content. For top band, derive the acceleration expression, test whether radius and mass really cancel, and check the no-slip assumption at higher angles.",
   "whereMarksAreLost": "Research design: only the standard objects, with no variation in k or angle. Data analysis: comparing only times, not against the model. Conclusion: not commenting on differences between measured and predicted a. Evaluation: ignoring rolling resistance and the hollow objects' wall thickness.",
   "dataNote": "A ramp, ruler and stopwatch are enough; light gates or video improve timing, which is the main uncertainty on a 1 to 2 s roll.",
   "verdict": "Accessible and testable against a firm prediction. Build your own objects, such as a can with added weights, to make it a personal investigation."
  },
  {
   "id": "rolling-cylinders-down-a-ramp-does-radius-or-mass-matter",
   "topic": "A.4",
   "topicName": "Rigid body mechanics",
   "level": "HL",
   "title": "Rolling cylinders down a ramp: does radius or mass matter?",
   "researchQuestion": "How does the radius of a solid wheel (2.0 cm to 8.0 cm, 6 values) affect its speed at the bottom of a 1.0 m ramp at 10°, with mass fixed?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Radius of a wheel or disc, using 6 discs cut from the same material, or a set of cylinders of different diameter. A separate second run varies mass at fixed radius over 5 values by adding equal masses to the rim or face.",
   "dependentVariable": "Time to travel a marked 1.0 m with a light gate pair or video analysis at 240 fps, giving linear speed v, and angular velocity ω = v/r. Five repeats per value.",
   "controlledVariables": "Ramp angle: fix with a clamp and check with a protractor or from height and length. Release point: mark start line and release without pushing. Surface: same track covering. Mass distribution: keep the shape and material consistent, or state clearly when it is changed.",
   "physicsNeeded": "Conservation of energy with rotation: mgh = ½mv² + ½Iω². For a solid uniform disc, v² = (4/3)gh, independent of mass and radius. Plot v² against h, or acceleration against sin θ, and compare the gradient with 2g/3 sin θ. The interesting result is that mass and radius should have no effect for the same shape.",
   "slVsHl": "HL only in the full form, because moment of inertia is in A.4. SL students can do a simplified version comparing acceleration with a sliding trolley. Top band: test different shapes (hoop, disc, sphere) and show that the ratio I/mr² decides the speed, not mass or size.",
   "whereMarksAreLost": "Research design: the question suggests mass and radius matter, so the hypothesis is wrong and the student never states the predicted null result. Data analysis: slipping treated as rolling. Conclusion: no comparison with the theoretical value. Evaluation: ignoring rolling friction and air resistance.",
   "dataNote": "Needs light gates or a phone in slow motion and a rigid ramp; the main uncertainty is release consistency and slipping at low friction.",
   "verdict": "Good HL choice, but reframe it: the physics says mass and radius should not matter, and testing that prediction is the strong version. Twist: use wheels from your own bike or skateboard."
  },
  {
   "id": "wheel-radius-and-the-torque-to-start-rotation",
   "topic": "A.4",
   "topicName": "Rigid body mechanics",
   "level": "HL",
   "title": "Wheel radius and the torque to start rotation",
   "researchQuestion": "How does the radius of a wheel, from 3.0 cm to 12.0 cm in six steps, affect the torque needed to make it just start turning on a fixed axle when a string wound on its rim is pulled by hanging masses?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Radius of the rim on which the string acts, 6 values from 3.0 to 12.0 cm, using stacked discs of different radii on one axle, each repeated 5 times.",
   "dependentVariable": "Mass added to a hanger until the wheel starts to turn, weighed on a balance. Torque is calculated as τ = mgr. Alternatively use a newton meter for the pull.",
   "controlledVariables": "Axle friction: same bearing, lubricated equally and checked with the wheel unloaded. Wheel mass and inertia: same stack of discs, only the string radius changes. String angle: kept tangent and horizontal with a pulley. Starting position: marked on the rim.",
   "physicsNeeded": "τ = Fr. If friction at the axle is constant the torque to overcome it is constant, so the mass needed is proportional to 1/r. Plot m against 1/r. The gradient gives the friction torque divided by g. A better version measures angular acceleration for a fixed hanging mass and uses τ = Iα.",
   "slVsHl": "The syllabus content sits in HL topic A.4, so this is an HL idea. Top band work finds the friction torque from the intercept, and repeats with a timed release to get α and I.",
   "whereMarksAreLost": "Research design: it is unclear what is meant by torque required, so the method measures something loose. Data analysis: no uncertainty from the stiction threshold. Conclusion: expecting torque to grow with r when it is really constant against friction. Evaluation: not addressing the axle friction as a systematic effect.",
   "dataNote": "Simple kit with a balance and stand, but the starting threshold is a judgement call, so the main uncertainty is the repeatability of stiction.",
   "verdict": "Only HL and the original question hides a trap, since the torque needed to beat friction hardly depends on radius. Rewrite it as the angular acceleration under a fixed torque and it becomes a solid investigation."
  },
  {
   "id": "cosmic-ray-muon-counts-at-two-altitudes-and-time-dilation",
   "topic": "A.5",
   "topicName": "Galilean and special relativity",
   "level": "HL",
   "title": "Cosmic ray muon counts at two altitudes and time dilation",
   "researchQuestion": "Does the observed fraction of atmospheric muons surviving from high altitude to sea level agree better with relativistic time dilation or with classical decay, given a mean muon lifetime of 2.2 microseconds?",
   "dataDifficulty": 3,
   "dataSource": "database",
   "sitesListingIt": 1,
   "independentVariable": "Altitude of the detector, using at least two published sites, or 5 or more altitudes if the dataset allows.",
   "dependentVariable": "Muon flux from published counts at each altitude; survival fraction is the ratio of fluxes, compared with exp(-t/tau) and exp(-t/(gamma tau)).",
   "controlledVariables": "Same muon energy or momentum band across datasets. Same detector type and angle to the vertical. Comparable atmospheric conditions. Same production height assumed in both predictions.",
   "physicsNeeded": "Time dilation t = gamma t0 and exponential decay N = N0 exp(-t/tau). Plot ln(N/N0) against altitude, and compare the gradient with the classical and relativistic predictions.",
   "slVsHl": "Relativity is HL only, so this is an HL idea. Top band: propagate uncertainties in flux and production height, and note energy loss in the atmosphere.",
   "whereMarksAreLost": "Research design: mixing datasets with different energy cuts. Data analysis: no uncertainty on flux. Conclusion: overclaiming from two points. Evaluation: ignoring the spread in production height and muon energy.",
   "dataNote": "Needs published flux data at known altitudes, which is hard to match in energy range; the uncertainty in production height and speed dominates.",
   "verdict": "Ambitious and hard to make clean with only secondary data. Consider a cosmic ray detector from a university outreach programme if your school has access, otherwise pick something simpler."
  },
  {
   "id": "specific-heat-capacity-of-salt-solutions-by-electrical-heating",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Specific heat capacity of salt solutions by electrical heating",
   "researchQuestion": "How does the specific heat capacity of sodium chloride solution change as its mass concentration rises from 0 to 250 g per kg of water, in 6 steps, measured by electrical heating in a lagged calorimeter?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 3,
   "independentVariable": "Salt mass per 100 g of water: 0, 5, 10, 15, 20, 25, 30 g (7 values), each run 3 times with a fresh solution.",
   "dependentVariable": "Temperature rise measured with a digital thermometer (0.1 °C) in a lagged polystyrene cup while a 50 W immersion heater runs for a fixed time. Energy comes from a joulemeter or from V, I and t. c is calculated from E = mcΔT with heat capacity of the cup included.",
   "controlledVariables": "Mass of solution weighed on a 0.01 g balance. Heater power checked by ammeter and voltmeter. Starting temperature about 20 °C every time. Lid, lagging and stirring rate kept the same. Heating time fixed so ΔT stays near 10 °C.",
   "physicsNeeded": "E = mcΔT, or VIt = (m c + C)ΔT. Plot ΔT against t for each concentration and use the gradient to find c. Then plot c against concentration; the expected fall is small, about a few per cent, so the linear fit and its uncertainty matter. Compare with published data.",
   "slVsHl": "SL students find c at each concentration and a trend. To reach the top band, correct for heat lost to the surroundings by plotting a full heating and cooling curve and discuss whether the change is bigger than the uncertainty. HL adds nothing specific.",
   "whereMarksAreLost": "Research design: changes in c are small compared with heat loss, so a weak method gives no visible trend. Data analysis: uncertainty bars larger than the effect. Conclusion: claiming a trend that the data cannot support. Evaluation: not quantifying the heat loss.",
   "dataNote": "Needs a joulemeter or power supply with meters, and a lagged calorimeter; heat loss and the small size of the effect are the main uncertainty.",
   "verdict": "Sensible but risky, because the effect is small and a sloppy setup will hide it. Pick it if you like careful calorimetry and are ready to state honestly whether a difference was detected."
  },
  {
   "id": "heat-flow-through-insulation-slabs-at-steady-state",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Heat flow through insulation slabs at steady state",
   "researchQuestion": "How does the thickness of foam or fibreboard insulation (5 to 30 mm, 6 values) affect the electrical power needed to keep a heated block at 60 °C?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Insulation thickness, 5 to 30 mm, six values made by stacking identical sheets, each measured with a calliper. Repeat each thickness twice or three times.",
   "dependentVariable": "Electrical power P = VI, from a heater and a power supply with a meter, once the temperature of the hot side has stayed constant for 5 minutes. Temperature by a probe on each face.",
   "controlledVariables": "Hot side temperature, held at 60 °C by adjusting the supply. Cold side or room temperature, recorded. Same area of contact and same heater. Same material, with edges sealed to reduce loss.",
   "physicsNeeded": "Conduction: P = kAΔT/d. Plot P (y) against 1/d (x). The gradient is kAΔT, so k can be found and compared with tables. Note that edge losses give a positive intercept.",
   "slVsHl": "SL students can produce the plot and estimate k. Excellent work adds a correction for edge loss, and a second material for comparison. HL does not change much here.",
   "whereMarksAreLost": "Research design: not waiting for steady state, so the reading is still changing. Data analysis: uncertainty in ΔT not propagated. Conclusion: k value not compared with a source. Evaluation: heat lost from the sides ignored, poor contact between layers and heater.",
   "dataNote": "Needs a heater, two thermometers and a power supply; the main issue is reaching steady state, which can take 20 minutes per run.",
   "verdict": "Worth choosing if you are patient, because the steady state design is sound. Twist: use the cooling curve of a wrapped can as a cheaper check and compare the two k values."
  },
  {
   "id": "linear-expansion-coefficient-of-a-heated-metal-rod",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Linear expansion coefficient of a heated metal rod",
   "researchQuestion": "How does the temperature rise (from 20 °C to 95 °C, 6 or more values) of a 0.50 m aluminium rod affect its extension, measured in mm?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Rod temperature, from 20 °C to 95 °C using steam or a hot water jacket, read at about 10 °C steps.",
   "dependentVariable": "Extension measured with a dial gauge or a micrometer-style lever arm to 0.01 mm, with temperature from a thermometer or thermocouple in contact with the rod. Repeat on cooling.",
   "controlledVariables": "Same rod, with initial length measured at room temperature. The rod insulated so the temperature is uniform along it. One end fixed rigidly. Same gauge position each run.",
   "physicsNeeded": "ΔL = αL₀ΔT. Plot ΔL against ΔT; the gradient is αL₀, so α = gradient/L₀. Compare with the tabulated value (about 23 × 10⁻⁶ /K for aluminium).",
   "slVsHl": "SL work extracts α and compares it with the literature. Top band handles thermal lag between water and rod, the expansion of the support frame and a hysteresis check on cooling.",
   "whereMarksAreLost": "Research design: extensions of about 1 mm are too small for a ruler. Data analysis: ignoring temperature uncertainty along the rod. Evaluation: heating the support and gauge as well as the rod.",
   "dataNote": "Needs a dial gauge and a steam or hot water jacket; the extension is tiny, so the gauge resolution and frame expansion dominate.",
   "verdict": "Worthwhile only with a dial gauge. A ruler cannot see the change. The twist is comparing aluminium, brass and steel rods."
  },
  {
   "id": "painted-cans-cooling-emissivity-and-convection-compared",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Painted cans cooling: emissivity and convection compared",
   "researchQuestion": "How does the surface finish of identical metal cans (matt black, gloss white, bare shiny, foil wrapped) change the initial cooling rate of water from 80 °C in a 20 min period?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Surface finish of the can, four to five types, each can filled with the same mass of water and tested three times.",
   "dependentVariable": "Water temperature with a probe every 30 s for 20 min. Calculate initial cooling rate dT/dt from the slope of the first few minutes, plus the total energy lost using Q = mcΔT.",
   "controlledVariables": "Same starting temperature of 80 °C. Same mass of water measured on a balance. Same can size and lid with insulated top. Same location out of draughts, room temperature logged, can raised on a cork mat.",
   "physicsNeeded": "Power radiated P = eσA(T⁴ − Ts⁴), plus convection. Plot ln(T − Ts) against t; the gradient gives the cooling constant which should be larger for higher emissivity. Convection is best reduced by a shield.",
   "slVsHl": "SL compares finishes qualitatively and ranks them. Higher marks come from separating radiation from convection, for example by repeating in a closed box, or by using an infrared thermometer to check surface temperature. HL can fit the T⁴ law.",
   "whereMarksAreLost": "Research design: temperature of the surroundings and the draughts not controlled, so differences are noise. Data analysis: comparing raw curves without a cooling constant or uncertainty. Evaluation: not admitting that convection and evaporation from the lid dominate over radiation at these temperatures.",
   "dataNote": "Needs identical cans, paint, a data logger or probe thermometer and a balance; main uncertainty is convection and evaporation swamping the radiation difference.",
   "verdict": "Good if you tackle the convection problem directly, since otherwise differences vanish. Twist: use a Leslie cube style set up or a lid to cut evaporation."
  },
  {
   "id": "spring-stiffness-of-a-steel-spring-in-warm-water",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Spring stiffness of a steel spring in warm water",
   "researchQuestion": "How does the spring constant k of a steel spring change as its temperature is raised from 20 °C to 80 °C in steps of 10 °C?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Temperature of the water bath around the spring, 20 to 80 °C, 7 values, three loading runs per temperature.",
   "dependentVariable": "Extension of the spring with a fixed 200 g load, read by a rule or a phone photo against a scale, and a digital thermometer for temperature. k = F/x is calculated, and better from the gradient of force against extension for 4 masses.",
   "controlledVariables": "Same spring throughout. Same masses used and the load applied for a fixed time. Spring fully in the water bath so the temperature is even. Reading taken when the temperature is stable, within 1 °C. Extension below the elastic limit.",
   "physicsNeeded": "Hooke's law F = kx. Plot k (y) against T (x). The temperature dependence is small, so expect a change of only a few percent over the range, well within noise. The gradient would give a temperature coefficient.",
   "slVsHl": "SL students can carry out the measurements and judge whether any trend beats the uncertainty. Reaching the top band needs uncertainty propagation on k and a proper conclusion, including 'no measurable change'. HL students can relate it to the temperature dependence of Young's modulus.",
   "whereMarksAreLost": "Research design: thermal expansion of the spring and the water buoyancy on the mass ignored. Data analysis: no error bars, so any trend is claimed without support. Conclusion: overclaiming a trend. Evaluation: rule resolution compared with the tiny effect not discussed.",
   "dataNote": "Needs a water bath, thermometer and a fine measurement of extension, and the effect is small compared with reading error.",
   "verdict": "Risky because the real effect is very small and may vanish in your uncertainty. It can still be a good result if you plan for a high-resolution measurement and honestly state a null outcome. Otherwise choose something with a clear signal."
  },
  {
   "id": "air-gap-width-in-a-double-glazed-model-window",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Air gap width in a double glazed model window",
   "researchQuestion": "How does the air gap between two glass panes, varied from 2 mm to 20 mm, affect the rate of cooling of 200 g of water at 60 °C in a box with a double glazed window?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Air gap width between two microscope slides or acrylic sheets, 2, 5, 8, 12, 16, 20 mm (6 values), 3 repeats each, set with spacers of measured thickness.",
   "dependentVariable": "Temperature of hot water in an insulated box read with a thermometer or data logger every 30 s for 10 min. Initial cooling rate in °C per s is taken from the gradient, and power lost is found using P = mcΔθ/Δt.",
   "controlledVariables": "Start temperature and volume of water identical. Window area the same, with other box walls thickly insulated. Room temperature and draughts monitored and kept constant. Gap sealed with tape to stop air exchange.",
   "physicsNeeded": "Conduction through a layer, P = kAΔT/d, and convection in a gap that becomes important once the gap is wide. Plot power lost against gap width and look for a minimum or levelling off, and 1/gap width if conduction alone is expected.",
   "slVsHl": "SL students can measure cooling rate and describe the trend using conduction and convection. Top band work identifies the gap at which convection takes over and uses U-values or thermal resistance to compare with the data.",
   "whereMarksAreLost": "Research design: heat escaping through the box walls swamps the window effect. Data analysis: comparing raw cooling curves rather than initial rates with uncertainties. Conclusion: claiming that larger gaps always insulate better. Evaluation: not quantifying how much heat leaks around the edges.",
   "dataNote": "Needs a well insulated box and a logger; the main uncertainty is heat loss through everything except the window.",
   "verdict": "A good idea if you can make the window the dominant loss path. Test a control run with the window blocked with foam to prove it, which makes the project yours."
  },
  {
   "id": "boiling-water-at-fixed-power-latent-heat-from-mass-loss",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Boiling water at fixed power: latent heat from mass loss",
   "researchQuestion": "How does the electrical power of an immersion heater, varied from 50 W to 250 W, affect the rate of mass loss of boiling water, and what value of specific latent heat of vaporisation does this give?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Heater power: 6 settings from about 50 W to 250 W, set with a variable DC supply and measured as V × I. Each held for 5 minutes of steady boiling, repeated 3 times.",
   "dependentVariable": "Mass of the beaker on a balance (±0.01 g) read every 30 s, giving the mass loss rate dm/dt from the gradient of a mass against time graph. Power from a voltmeter and ammeter.",
   "controlledVariables": "Starting water mass: same 300 g each run. Container: same insulated beaker with the same partial lid. Heater position: clamped, fully immersed, not touching the base. Water: start every run already boiling, to ignore warm-up.",
   "physicsNeeded": "P = L (dm/dt) + P_loss. Plot P (y) against dm/dt (x): gradient is L, and the y-intercept is the power lost to surroundings. Compare with 2.26 MJ/kg.",
   "slVsHl": "SL: plot P against dm/dt, read L, and comment on the intercept. Top band or HL depth: consider whether P_loss changes with power, use error bars from the repeats, and discuss steam condensing on the lid and the heater lead.",
   "whereMarksAreLost": "Research design: including the warm-up period in the mass loss. Data analysis: no uncertainty on the gradient, or forcing the line through the origin. Conclusion: not explaining why L comes out too low or too high. Evaluation: ignoring condensed steam or convection forces on the balance.",
   "dataNote": "Needs a mains-safe immersion heater or a low-voltage coil, and a balance able to handle a hot beaker; the main uncertainty is steam condensing and buoyancy forces from the rising steam.",
   "verdict": "A strong experiment because the intercept gives you a physical result about heat loss. Take care with electrical safety and keep the water level constant."
  },
  {
   "id": "comparing-thermal-conductivity-of-metal-rods-by-steady-state",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Comparing thermal conductivity of metal rods by steady state",
   "researchQuestion": "How does the thermal conductivity of copper, aluminium, brass and steel rods of equal length 20 cm and diameter 1 cm affect the temperature gradient along each rod at steady state with one end in boiling water?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Metal type, four to five metals (copper, aluminium, brass, mild steel, and stainless steel if available), with 6 thermometer positions along each rod as second variable.",
   "dependentVariable": "Temperature at fixed points along each rod from thermocouples or a multi-channel logger, reading to 0.1 °C. Temperature gradient dT/dx found from a plot, then relative conductivity k ∝ 1/gradient.",
   "controlledVariables": "Rod length and diameter measured with vernier callipers. Hot end held at 100 °C in a kettle or steam. Cold end in an ice bath or at fixed room temperature. Rods lagged with the same insulation and steady state judged when the readings stop changing for two minutes.",
   "physicsNeeded": "Fourier conduction P = kA(ΔT/Δx). Plot temperature against distance along the rod, gradient is proportional to 1/k for a constant heat flow. Compare with the ratio of literature k values.",
   "slVsHl": "SL students can rank the metals and compare gradients. Top band work estimates the heat flow from the cold end water (mcΔT/t) to get an absolute k. HL not needed.",
   "whereMarksAreLost": "Research design: 'heat exchanger efficiency' is not measured, so the RQ should be about conductivity. Data analysis: not reaching steady state before reading. Evaluation: side losses from unlagged rods.",
   "dataNote": "Needs rods of equal size and several thermometers or thermocouples; lateral heat loss and thermal contact at the hot end are the main uncertainties.",
   "verdict": "Sound if you drop the heat exchanger language and measure k properly. Twist: add a metal from something you own, such as a spoon, and predict its gradient first."
  },
  {
   "id": "cooling-constant-of-hot-water-and-open-surface-area",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Cooling constant of hot water and open surface area",
   "researchQuestion": "How does the open surface area of hot water, varied from 20 cm² to 80 cm² using cylindrical containers of different diameter, affect the cooling constant k in Newton's law of cooling?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Exposed surface area: 5 to 6 different beakers or cups with diameters from about 5 cm to 10 cm, giving areas from 20 cm² to 80 cm². Two runs each.",
   "dependentVariable": "Temperature logged every 30 s for 30 minutes with a temperature probe (±0.1 °C). The constant k is found from the gradient of ln(T − T_room) against time.",
   "controlledVariables": "Water volume: use 200 ml in each, which changes the depth, so consider also a set with equal depth. Starting temperature: 80 °C. Room temperature: measured with a second probe, no draughts. Container material: same thin-walled glass or metal, insulated on the sides and base.",
   "physicsNeeded": "dT/dt = −k(T − T_env), so ln(T − T_env) = −kt + constant. Plot ln(T − T_env) against t, gradient −k. Then plot k against area A: if evaporation and convection from the top dominate, k should be roughly proportional to A/(mc).",
   "slVsHl": "SL: extract k from each run and plot k against area. Top band or HL depth: separate the evaporation contribution using lids, and explain the change from the exponential model at high temperature difference.",
   "whereMarksAreLost": "Research design: changing the water depth and mass together with the area. Data analysis: fitting a single exponential to the whole curve, including the early part where evaporation makes it non-linear. Conclusion: claiming proportionality without checking the fit. Evaluation: not considering the changing room temperature.",
   "dataNote": "A temperature probe with a data logger is helpful; without one, manual readings every minute work but are noisier. The main uncertainty is evaporation and draughts.",
   "verdict": "A worthwhile investigation if you keep it about the cooling constant and not a general talk on cooling. Insulating the sides is the twist that isolates the top surface."
  },
  {
   "id": "cooling-constant-of-water-in-cups-of-different-surface-area",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Cooling constant of water in cups of different surface area",
   "researchQuestion": "How does the open top area A of a beaker (A = 20 to 80 cm², five sizes) filled with 150 g of water at 80 °C affect the cooling constant k over 20 minutes?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Open surface area A of five similar cylindrical containers, 20, 32, 45, 60, 80 cm², from the measured diameters, each run three times.",
   "dependentVariable": "Water temperature every 30 s from a digital thermometer or logger; k from the gradient of ln(T − T_room) against time.",
   "controlledVariables": "Mass of water: 150 g on a balance. Starting temperature: 80 °C by the kettle and thermometer. Room temperature: recorded each run, drafts avoided by working in one closed room. Container material: all glass or all the same plastic, with the same lid condition.",
   "physicsNeeded": "Newton's law of cooling: dT/dt = −k(T − T_room), so ln(T − T_room) against t is a straight line with gradient −k. Then plot k against A to find whether it is proportional. Evaporation from an open surface adds a second loss path.",
   "slVsHl": "SL students can complete the two step analysis. To reach the top band, separate evaporation by covering the cup with a lid and comparing, and use the linearity of the ln graph residuals to state where Newton's law stops holding at large temperature differences.",
   "whereMarksAreLost": "Research design: shape, material and area varied at once. Data analysis: k found from a curve fit with no check of the linear plot. Evaluation: ignoring evaporation, so the area effect is not just conduction and radiation.",
   "dataNote": "A kettle, thermometer or logger and a set of beakers are enough; room drafts and evaporation are the main uncertainties.",
   "verdict": "A good sound choice if only one thing changes. Choose area with a fixed material, then repeat with lids on to isolate evaporation, which makes it your own."
  },
  {
   "id": "cooling-curves-of-water-oil-and-salt-solution",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Cooling curves of water, oil and salt solution",
   "researchQuestion": "How does the mass fraction of salt in water (0 to 20 % in 5 steps) affect the initial cooling rate of 150 g samples starting at 70 °C in identical lidded beakers?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Salt mass fraction, 0, 5, 10, 15, 20 %, made up on a balance, three runs each. Cooking oil can be added as an extra comparison liquid.",
   "dependentVariable": "Temperature every 30 s over 15 minutes from a digital thermometer; cooling rate from the initial gradient of the T against t graph, and k from ln(T − T_room) against t.",
   "controlledVariables": "Sample mass: 150 g on a balance. Start temperature: 70 °C. Container and lid: same beaker and lid for each run. Room temperature: measured each run, no drafts. Stirring: same gentle stir before each reading.",
   "physicsNeeded": "Rate of energy loss P = m c dT/dt, and Newton's law of cooling gives dT/dt = −k(T − T_room). The specific heat capacity of the solution falls with salt content, so plot k or the initial rate against mass fraction, and compare a calculated c with the data value.",
   "slVsHl": "Suitable for SL. Top band work relates the change in cooling rate to the change in specific heat capacity and to the surface loss, and separates evaporation by using lids.",
   "whereMarksAreLost": "Research design: different liquids vary density, volume and specific heat at once. Data analysis: reading cooling rate from a single point. Evaluation: evaporation and convection differences not addressed.",
   "dataNote": "A kettle, thermometer or logger, beakers and salt are enough; evaporation and non-uniform temperature in the liquid are the main uncertainties.",
   "verdict": "Better than comparing random liquids, because salt fraction is a continuous variable with a clear expected trend. Use lids and equal mass to get a fair test."
  },
  {
   "id": "cooling-of-salt-solutions-of-different-density",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Cooling of salt solutions of different density",
   "researchQuestion": "How does the mass of potassium chloride dissolved in 200 g of hot water, from 0 to 15 g in steps of 3 g, affect the initial cooling rate of the solution over 10 minutes?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Mass of KCl dissolved in 200 g of water: 0, 3, 6, 9, 12 and 15 g. Two or three repeated cooling runs for each.",
   "dependentVariable": "Temperature from a digital thermometer or logger every 30 s from about 70 °C. Initial cooling rate found from the gradient of the first few minutes of the temperature time graph. Density checked with a measuring cylinder and balance.",
   "controlledVariables": "Starting temperature: 70 °C for every run. Water mass: 200 g weighed. Container: the same insulated cup with lid. Room temperature and draughts: same bench, recorded at start and end.",
   "physicsNeeded": "Newton's law of cooling, dT/dt = −k(T − T_room). Plot ln(T − T_room) against t and use the gradient as −k. Salt changes the specific heat capacity and mass, so compare k with a prediction from c of the solution.",
   "slVsHl": "SL: cooling curves and gradients, with a clear link to heat capacity. Top band: linearise with ln, predict k from the changed heat capacity and separate the effect of evaporation. HL: nothing extra needed.",
   "whereMarksAreLost": "Research design: calling density the variable when mass of salt is what is changed, and dissolving not being complete. Data analysis: rate taken from two points. Evaluation: not addressing that evaporation and lid losses dominate over a small effect.",
   "dataNote": "Thermometer or logger, cups and a balance; the effect is small, so repeats and a lid are essential to see any trend above scatter.",
   "verdict": "Fine but the expected effect is small and easily lost in noise. Better to frame it around heat capacity and check your prediction, not density."
  },
  {
   "id": "cooling-of-warm-water-in-wrapped-containers",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Cooling of warm water in wrapped containers",
   "researchQuestion": "How does the initial cooling rate of 200 mL of water, starting at 60 °C in a wrapped beaker, depend on the thickness of a wool layer, from one to six layers, over 15 minutes?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Number of wool layers wrapped round the beaker: 1, 2, 3, 4, 5 and 6 (6 values), plus an unwrapped control. Each value is repeated 3 times.",
   "dependentVariable": "Water temperature every 30 s for 15 minutes, using a digital thermometer or a temperature probe. Cooling rate is the gradient of the temperature against time in the first 5 minutes, or the fitted decay constant of the whole curve.",
   "controlledVariables": "Same beaker and 200 mL of water, measured in a measuring cylinder. Starting temperature 60 °C, set with a kettle and a thermometer. Room temperature logged and draughts avoided, with a lid on the beaker. Same wool, with the layer thickness measured with a ruler and the wrap tight each time.",
   "physicsNeeded": "Newton's law of cooling: dT/dt = −k(T − Troom), so ln(T − Troom) against t is a straight line with gradient −k. Rate of energy loss P = mc dT/dt. Plot k or P against the number of layers, or against the inverse of thickness, to test whether conduction through the layer, where P ∝ A ΔT/d, matches the data. Comparing different materials, as in the original idea, is better done with equal thickness.",
   "slVsHl": "SL students plot cooling curves and compare rates for each thickness. Top band work linearises with ln(T − Troom), links k to thermal conductivity, and discusses heat lost through the lid and base. HL students can estimate effective thermal conductivity of the wool from the gradient and compare it with a published value.",
   "whereMarksAreLost": "Research design: comparing materials of different thickness mixes two variables, so fix one. Data analysis: reading a hand held thermometer with no uncertainty and using one run only. Conclusion: claiming a material is better without a numerical value. Evaluation: heat loss from the top and base, and uneven wrapping, are seldom addressed.",
   "dataNote": "Needs beakers, a kettle, a thermometer or probe, a stopwatch and wool. The main uncertainty is uneven wrapping and evaporation from the water surface.",
   "verdict": "Easy and reliable, but common as a topic. Fix the thickness question or the material choice so it is measurable. The link to animals is only an analogy. Testing your own gear, such as a jacket fabric or a hot water bottle cover, would make it personal."
  },
  {
   "id": "cooling-rate-of-hot-water-in-containers-of-different-surface-area",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Cooling rate of hot water in containers of different surface area",
   "researchQuestion": "How does the exposed surface area of hot water (from 20 cm² to 80 cm², 6 values) in cylindrical beakers affect the initial rate of cooling in °C per minute, starting at 80 °C?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Open surface area of the water, changed by using 6 cylindrical containers of different diameter (about 5 to 10 cm), each with the same mass of water. Three repeats per container.",
   "dependentVariable": "Temperature against time with a digital thermometer or temperature probe and datalogger, every 30 s for 10 min. The initial cooling rate is found from the gradient of a tangent, or from a fit of the first few minutes.",
   "controlledVariables": "Starting temperature: heat every sample to 80 °C and start timing at the same reading. Mass of water: weigh on a balance. Room conditions: same bench, no draughts, door closed. Container material and lid: use identical thin metal or plastic and either no lid throughout or a lid throughout.",
   "physicsNeeded": "Newton's law of cooling and the rate of energy loss P = hAΔT (with evaporation as an extra effect). Plot initial cooling rate against surface area; a straight line through the origin supports proportionality, and the gradient links to h and to the mass and specific heat capacity of the water. Note that the original wording heats objects, so cooling is the cleaner measurable version.",
   "slVsHl": "SL: measure rates, plot rate against area, state whether it is proportional. Top band or deeper: separate evaporation from convection by comparing lidded and open runs, and fit exponential decay to extract a cooling constant per container.",
   "whereMarksAreLost": "Research design: depth of water changes with area if volume is not fixed, and this is missed. Data analysis: tangent gradients drawn by eye with no uncertainty. Conclusion: claiming proportionality without comparing the fit to the uncertainty. Evaluation: ignoring evaporation and the heat lost through the sides and base.",
   "dataNote": "Beakers or cans, thermometer or probe, balance and stopwatch are enough; the main uncertainty is evaporation and draughts changing the loss between runs.",
   "verdict": "Worth doing if you flip it to cooling, which is far easier to measure than heating. Twist: use real objects like a mug shape you actually own and link the result to why soup cools faster in a wide bowl."
  },
  {
   "id": "correcting-heat-loss-in-a-specific-heat-capacity-block",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Correcting heat loss in a specific heat capacity block",
   "researchQuestion": "How does the thickness of foam insulation around a 1.0 kg aluminium block, varied from 0 cm to 5 cm in 1 cm steps, affect the specific heat capacity calculated from a 10 minute electrical heating run?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Thickness of insulation (0 cm to 5 cm in 1 cm steps, 6 values, 3 repeats each).",
   "dependentVariable": "Joulemeter or voltmeter and ammeter give the electrical energy E = VIt. A thermometer or temperature probe gives ΔT. Apparent c = E/(mΔT), then corrected using the cooling curve measured after heating stops.",
   "controlledVariables": "Heater power: a stabilised supply and the same 12 V, 50 W heater. Heating time: 600 s with a timer. Starting temperature: block at room temperature, checked before each run. Room conditions: away from draughts, with ambient temperature recorded.",
   "physicsNeeded": "Energy balance E = mcΔT + heat lost. Plot the apparent c against insulation thickness and show how it tends towards the true value of about 900 J kg⁻¹ K⁻¹. Alternatively, plot temperature against time on the cooling curve and use the loss rate to add back the lost thermal energy.",
   "slVsHl": "SL: measure and plot apparent c against thickness, and compare with the accepted value. Top band: model the loss with Newton's cooling law from the cooling curve and correct each result. HL is not needed.",
   "whereMarksAreLost": "Research design: thermometer not in good contact, with no oil in the hole. Data analysis: no percentage difference from the accepted value or uncertainty propagated. Conclusion: claiming insulation removes all loss. Evaluation: ignoring the thermal energy in the heater and the lag in temperature.",
   "dataNote": "A block with a heater and probe hole is standard school kit; the main uncertainty is temperature lag in the block and heat loss.",
   "verdict": "Turns a routine practical into an inquiry about systematic error. Worth choosing if you do the cooling curve correction, otherwise it is just a familiar experiment."
  },
  {
   "id": "counting-glass-panes-in-a-model-window",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Counting glass panes in a model window",
   "researchQuestion": "How does the number of glass panes, from 1 to 5 with 5 mm air gaps, affect the power lost from hot water at 60 °C through a model window?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Number of panes in the window, 1 to 5 (5 values), stacked with equal 5 mm spacers, 3 repeats each.",
   "dependentVariable": "Water temperature against time with a thermometer or logger, giving the initial cooling rate. Power lost is found from mcΔθ/Δt and thermal resistance from R = ΔT/P.",
   "controlledVariables": "Same water mass and start temperature. Same window area and gap width. Box walls insulated identically. Same room with no draughts, and the room temperature recorded each run.",
   "physicsNeeded": "Thermal resistances of layers in series add, so total resistance should grow linearly with the number of gaps. Plot thermal resistance (ΔT/P) against number of panes; the gradient is resistance per pane and the intercept gives the box's other losses.",
   "slVsHl": "SL students show that heat loss falls as panes are added and explain why. Top band work tests the series resistance model and finds diminishing returns from a fixed total thickness.",
   "whereMarksAreLost": "Research design: gaps not kept equal as panes are added. Data analysis: not converting to resistance so the linear model cannot be tested. Conclusion: ignoring the intercept from other heat paths. Evaluation: not addressing edge leaks and seal quality.",
   "dataNote": "Uses microscope slides or acrylic sheets, spacers and a logger; the main uncertainty is leaks and stacking alignment.",
   "verdict": "Fine but close to the gap width idea, so pick one. The series resistance graph gives you a clean model to test, which is the real strength here."
  },
  {
   "id": "cylinder-shape-and-newton-cooling-of-hot-water",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Cylinder shape and Newton cooling of hot water",
   "researchQuestion": "How does the ratio of exposed surface area to volume, varied from about 0.5 cm^-1 to 1.5 cm^-1 using six metal cylinders holding 200 cm^3 of water each, affect the initial cooling constant k of water starting at 80 °C?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Ratio A/V of the container, changed by using six thin-walled aluminium or steel cans of different radius and height, all filled with the same 200 cm^3 of water. A/V is calculated from measured diameter and water height, including the open top or a fitted lid. Range about 0.5 to 1.5 cm^-1, three trials per shape.",
   "dependentVariable": "Water temperature read every 30 s for 20 minutes with a digital temperature probe and data logger (or thermometer plus stopwatch). Ln(T - T_room) is plotted against time for the first 10 to 15 minutes, and the gradient magnitude gives the cooling constant k in s^-1.",
   "controlledVariables": "Starting temperature of 80 °C, checked with the probe before each run. Water volume of 200 cm^3, measured with a measuring cylinder. Room temperature, recorded throughout and kept steady by a closed room with no draught. Lid material and stirring, using the same insulating lid and one gentle stir before each reading, and containers standing on the same insulating mat.",
   "physicsNeeded": "Rate of heat loss is proportional to surface area and to the temperature difference with the surroundings, so dT/dt = -k(T - T_room) with k proportional to A/(mC), that is to A/V for the same water. Plot ln(T - T_room) against t: the gradient is -k. Then plot k against A/V: a straight line through the origin supports proportionality, and its gradient links to the heat transfer coefficient and water's specific heat capacity.",
   "slVsHl": "An SL student can measure cooling curves, extract k for each shape and show that k rises with A/V, with uncertainty bars from repeats. Top band work separates the surface losses (convection, evaporation, radiation) by using lids, tests whether the line really passes through the origin, and explains any intercept as heat lost through the base or the lid. HL depth can add a discussion of radiative loss with the T^4 law and a comparison of the fitted heat transfer coefficient with a literature value.",
   "whereMarksAreLost": "Research design: A/V changed while wall material, thickness and lid are also different, so several variables change together; open top ignored in the area calculation. Data analysis: fitting the whole curve including the late stage near room temperature, where the reading noise dominates, and not propagating uncertainty in A/V. Conclusion: claiming proportionality without checking the intercept or comparing k values with the spread from repeats. Evaluation: not discussing evaporation and uneven temperature inside the water as systematic errors.",
   "dataNote": "Needs only cans, a thermometer or probe, a kettle and a stopwatch, and the main uncertainty is evaporation and draughts changing the loss from run to run.",
   "verdict": "Simple and safe, and it works well if you keep the material fixed and analyse ln(T - T_room) rather than just comparing final temperatures. Personal twist: choose real objects such as a mug, a flask and a saucepan and ask which shape a coffee shop should use to keep drinks warm longest."
  },
  {
   "id": "does-water-s-specific-heat-capacity-drift-between-20-and-70-c",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Does water's specific heat capacity drift between 20 and 70 °C?",
   "researchQuestion": "Does the specific heat capacity of water, measured with a 50 W immersion heater, change when its starting temperature is 20, 30, 40, 50, 60 and 70 °C?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Starting water temperature, six values from 20 °C to 70 °C, each repeated three times.",
   "dependentVariable": "Temperature rise over a fixed 120 s of heating, from a digital thermometer or temperature probe reading to 0.1 °C. Energy from joulemeter or from V·I·t. Calculate c = E/(mΔT).",
   "controlledVariables": "Water mass 200 g by balance each time. Same heating time and same power, checked with a voltmeter and ammeter. Same insulated polystyrene cup with lid. Stirring at a constant rate before every reading.",
   "physicsNeeded": "Q = mcΔT and E = VIt. Plot calculated c against starting temperature and see if the gradient is zero within uncertainty. Heat loss grows with temperature, so a correction from a cooling curve is expected.",
   "slVsHl": "SL students can get a flat line and a value near 4.18 kJ kg⁻¹ K⁻¹, then argue why. Stronger work measures heat loss with a heater-off cooling run at each temperature and subtracts it. Accurate handling of the fact that real c varies by under 1% is what pushes it into top band.",
   "whereMarksAreLost": "Conclusion: claiming c changes when the trend is just heat loss at higher temperatures. Data analysis: no propagated uncertainty on ΔT, which is small. Evaluation: no quantified heat loss correction.",
   "dataNote": "Needs an immersion heater and a good thermometer; the dominant uncertainty is heat loss to the air at high starting temperatures.",
   "verdict": "Good if you accept that the true answer is nearly flat and make heat loss the real subject. Twist: try a liquid you use at home, such as olive oil, where c does change measurably."
  },
  {
   "id": "evaporation-rate-against-open-surface-area-of-water",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "SL",
   "title": "Evaporation rate against open surface area of water",
   "researchQuestion": "How does the evaporation rate of water at 22 °C vary with exposed surface area, using circular dishes of diameter 4, 6, 8, 10, 12 and 14 cm over 24 hours?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Open surface area, six dishes of known diameter with area πd²/4, from about 13 to 154 cm².",
   "dependentVariable": "Mass lost over 24 hours, measured with a 0.01 g balance at the start and end. Rate of evaporation is mass lost divided by time. Repeat each dish three times.",
   "controlledVariables": "Same starting water depth in every dish (not volume), because depth might matter. Same room, shelf and temperature, with a thermometer and humidity reading. No draughts, dishes kept in a closed cupboard or away from windows. Same water source.",
   "physicsNeeded": "Evaporation as loss of the highest energy molecules, and rate of mass loss expected proportional to area. Plot mass loss rate against area, expecting a straight line through the origin, with gradient as mass flux per unit area. Link to latent heat by calculating the energy removed, L·Δm.",
   "slVsHl": "SL students can do a straight line fit and interpret the gradient. To reach top band, compare with a model using vapour pressure, or show edge effects make the line curve. HL adds nothing specific.",
   "whereMarksAreLost": "Research design: controlling volume instead of depth, so dishes of different area have different depths. Data analysis: no uncertainty on area or drifting room humidity. Evaluation: missing that air over small dishes is affected by rim effects.",
   "dataNote": "Needs a balance to 0.01 g and patience; the main uncertainty is humidity and air movement changing between days.",
   "verdict": "An easy and safe choice that can score well if you record the humidity and test for proportionality. Twist: use a dish from your own kitchen and place a control dish beside each run."
  },
  {
   "id": "ice-melting-in-warm-water-latent-heat-by-mixing",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Ice melting in warm water: latent heat by mixing",
   "researchQuestion": "How does the initial temperature of 150 g of water, varied from 30 °C to 70 °C in steps of 10 °C, affect the value of the specific latent heat of fusion of ice, found from the final mixing temperature?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Initial water temperature: 30, 40, 50, 60, 70 °C (5 values), 3 repeats each, using a fresh ice cube of about 20 g every time.",
   "dependentVariable": "Final equilibrium temperature read with a digital thermometer (±0.1 °C) and masses from a balance (±0.01 g). Latent heat L is calculated from energy lost by the water and calorimeter equalling energy gained by the melting ice and its meltwater.",
   "controlledVariables": "Ice mass: weighed after the cube is dried and by the rise in cup mass at the end. Ice starting temperature: use ice sitting in melting ice water at 0 °C, then blotted. Calorimeter: same polystyrene cup and lid every time. Stirring: constant gentle stirring until the minimum temperature is reached.",
   "physicsNeeded": "Q = mcΔT and Q = mL. Energy balance: m_w c_w (T_i − T_f) + C_cal (T_i − T_f) = m_ice L + m_ice c_w (T_f − 0). Plot m_w(T_i − T_f) against m_ice, or plot energy lost by the warm water against ice mass melted at fixed T_i. Gradient gives L, and a flat trend of L against T_i shows the method is consistent.",
   "slVsHl": "SL: calculate L for each temperature, compare with 334 kJ/kg and comment on the trend. Top band or HL depth: measure the calorimeter heat capacity in a separate run, propagate uncertainties, and model heat gain from the room to explain a drift of L with starting temperature.",
   "whereMarksAreLost": "Research design: forgetting to dry the ice, so surface water adds mass and gives too low an L. Data analysis: not including the calorimeter or the warming of meltwater from 0 °C. Conclusion: claiming a physical dependence of L on temperature when the spread is within uncertainty. Evaluation: not quantifying heat exchange with the room.",
   "dataNote": "Polystyrene cup, thermometer, balance and ice are enough; the main uncertainty is water clinging to the ice and heat gained from the room.",
   "verdict": "Common school experiment, but the twist of testing whether L depends on starting temperature turns it into a proper test of the method. Worth choosing if you are careful with the ice mass and treat the flat trend as a result."
  },
  {
   "id": "insulating-a-hot-can-with-household-materials",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Insulating a hot can with household materials",
   "researchQuestion": "How does the thickness x of a wool wrapping (x = 0 to 2.0 cm in 5 steps) round a 250 mL aluminium can affect the time for 200 g of water to cool from 80 °C to 50 °C?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Thickness x of a single insulator, 0, 0.5, 1.0, 1.5, 2.0 cm (measured with callipers), three runs each. A second material can be repeated at the same thicknesses for comparison.",
   "dependentVariable": "Time to cool by 30 K with a thermometer or logger, and the average power loss P = m c ΔT / t calculated from it.",
   "controlledVariables": "Water mass: 200 g on a balance. Start temperature: 80 °C. Lid: same lid, insulated in the same way. Room temperature: recorded and drafts avoided.",
   "physicsNeeded": "Conduction through a layer: P = k A ΔT / x, though for a cylinder the log form is more accurate. A plot of 1/P against x is expected to be straight with gradient related to 1/(kA ΔT); the conductivity of the material is found and compared with a published value. Average power from P = m c ΔT / t.",
   "slVsHl": "Entirely SL. Top band work notes the cylindrical geometry, uses a mean temperature difference over the run, and compares the thermal conductivity found with the data value for wool or for still air.",
   "whereMarksAreLost": "Research design: different materials compared with different thickness and packing. Data analysis: no conversion to a quantity that can be compared with the literature. Evaluation: heat lost through the lid and base not treated.",
   "dataNote": "Only cans, a thermometer and materials are needed; heat lost through the uninsulated top and base is the main uncertainty.",
   "verdict": "Fine, but a which is best comparison is thin. Vary thickness of one material and extract a conductivity, and it becomes a real investigation."
  },
  {
   "id": "linear-expansion-coefficients-of-metal-rods-heated-by-steam",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Linear expansion coefficients of metal rods heated by steam",
   "researchQuestion": "How does the extension of a 60 cm rod of aluminium, brass and steel change as its temperature rises from 20 °C to 95 °C in steps of about 15 °C, and what are the expansion coefficients?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Temperature rise of the rod (about 6 values from 20 °C to 95 °C), with three rod materials, so the metal is a second variable; rods heated in a steam jacket or a hot water tube.",
   "dependentVariable": "Extension ΔL measured with a dial gauge or a micrometer against a fixed stop (mm, resolution 0.01 mm), with the temperature from a digital thermometer at the middle of the rod; α is calculated from the gradient.",
   "controlledVariables": "Initial length: same 60.0 cm, measured with a rule at 20 °C. Rod cross-section: rods of the same diameter. Heating: same steam generator and time to reach equilibrium. Fixing: same clamp arrangement so the rod pushes only on the gauge.",
   "physicsNeeded": "ΔL = αL₀ΔT. Plot ΔL (y) against ΔT (x): the gradient is αL₀, so α = gradient / L₀. Compare α for the three metals with the data booklet.",
   "slVsHl": "SL: one linear graph per metal and a comparison with data values. Top band: repeat on heating and cooling to test for lag, treat the extension of the gauge itself, and use the fractional uncertainty. Plastics and ceramics from the original are not practical in school and add nothing.",
   "whereMarksAreLost": "Research design: the input idea is too vague, since 'material type' and temperature are both varied with no method for measuring small changes. Data analysis: the extension is only about 1 mm, so the relative uncertainty is large and often not shown. Conclusion: no comparison with the accepted values. Evaluation: the temperature along the rod is not uniform and the thermometer reads the steam, not the metal.",
   "dataNote": "Needs a steam generator, expansion rods and a dial gauge; the main uncertainty is the small extension and uneven rod temperature.",
   "verdict": "A good practical because there is a clear linear model, but only with a dial gauge, since a ruler is too coarse. The twist is to compare three metals and check the values against the data booklet."
  },
  {
   "id": "metal-specific-heat-capacity-by-method-of-mixtures",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Metal specific heat capacity by method of mixtures",
   "researchQuestion": "How does the specific heat capacity of aluminium, brass, copper, iron and zinc samples of about 100 g each, measured by dropping them from boiling water at 100 °C into 150 g of water in a polystyrene cup, compare with data book values, in J kg⁻¹ K⁻¹?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Metal type: 5 different metals, each with 5 repeated trials. An extension could vary the mass of one metal over 5 values from 50 g to 250 g.",
   "dependentVariable": "Water temperature rise read with a digital thermometer (±0.1 °C) or temperature probe. Specific heat is calculated from energy lost by the metal equal to energy gained by the water and cup.",
   "controlledVariables": "Water mass, weighed on a balance to ±0.1 g each trial. Starting water temperature, checked with the same thermometer. Metal start temperature, held by leaving it in boiling water for 5 minutes. Transfer time and lid use, kept short and consistent to limit heat loss.",
   "physicsNeeded": "m_metal c_metal (T_hot − T_final) = m_water c_water (T_final − T_cold) plus a cup correction. Plot energy gained by the water against m_metal(T_hot − T_final) for a single metal with varying mass, so the gradient equals c_metal. Otherwise compare calculated c with accepted values.",
   "slVsHl": "SL students calculate c for each metal and compare percentage differences with book values. Top band work models heat losses, for example by plotting a cooling curve of the cup and extrapolating back to the mixing time, and uses uncertainty propagation carefully. HL adds nothing syllabus-wise, so depth comes from the treatment of systematic error.",
   "whereMarksAreLost": "Research design: not accounting for the cup's heat capacity or heat lost during transfer. Data analysis: uncertainty on a small temperature rise is large and often ignored. Conclusion: claiming agreement without a quantitative comparison to the accepted value. Evaluation: blaming vague 'heat loss' with no estimate of its size or direction.",
   "dataNote": "Needs a kettle, polystyrene cups, a balance and a thermometer. The main uncertainty is heat loss during transfer and the small temperature rise for low-mass samples.",
   "verdict": "Safe and doable, but well used, so it only stands out if you treat heat loss quantitatively. Twist: use the same metals as your school's own kitchen or workshop offcuts and test whether alloys differ from pure metals."
  },
  {
   "id": "rate-of-heat-conduction-through-different-sheet-materials",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Rate of heat conduction through different sheet materials",
   "researchQuestion": "How does the rate of heat flow through 5 mm thick sheets of cork, wood, acrylic, glass and aluminium compare, using the temperature rise of 100 g of water over 10 minutes with a 60 °C source on the other side?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Sheet material (five types) with identical thickness, plus optionally thickness of one material at 2, 4, 6, 8, 10 mm.",
   "dependentVariable": "Temperature of a water-filled aluminium calorimeter on the cool side recorded every 30 s with a digital thermometer or probe (°C); heat flow rate P = mcΔT/Δt from the early linear section.",
   "controlledVariables": "Heat source temperature: water bath held at 60 °C with a thermometer. Contact area: same cut circle, same clamp pressure. Thickness: measured with a micrometer or calipers. Starting temperature of water and room conditions the same, with lagging around the sides.",
   "physicsNeeded": "P = kAΔT/d. Plot P against 1/d for one material: the gradient equals kAΔT and gives k. For different materials, compare k with database values. Note that ΔT changes during the run, so use initial gradients.",
   "slVsHl": "SL: rank materials and estimate k for each. Top band: correct for heat losses with a blank control, account for contact resistance, and test the linear relation with thickness.",
   "whereMarksAreLost": "Research design: 'heat transfer rate' left undefined and thickness not matched. Data analysis: using the whole cooling curve rather than the initial rate. Conclusion: no comparison with tabulated conductivity. Evaluation: side losses and poor contact are large and usually not quantified.",
   "dataNote": "Needs a temperature probe, hot water bath, calorimeter and sheets; the main uncertainty is heat loss to the surroundings and contact quality.",
   "verdict": "Fine if you tie it to P = kAΔT/d and get real k values. Give it a personal angle such as testing building or clothing insulation you can actually buy."
  },
  {
   "id": "regelation-wire-cutting-through-ice-under-load",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "HL",
   "title": "Regelation: wire cutting through ice under load",
   "researchQuestion": "How does the load on a thin wire (0.5 to 5.0 kg in six steps) affect the speed at which it passes through a block of ice at 0 °C?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Hanging mass on a 0.3 mm steel wire, six values from 0.5 kg to 5.0 kg, three runs each.",
   "dependentVariable": "Distance moved by the wire through the ice, measured with a ruler and a stopwatch or video, then speed = distance/time.",
   "controlledVariables": "Ice block from one freezer batch and started at 0 °C, shown by a melting ice slush. Wire diameter and length kept constant. Room temperature recorded and the block insulated, or run in a cold room. Same contact width on the ice.",
   "physicsNeeded": "Pressure p = F/A with A = wire diameter × contact length. The melting point shifts with pressure, dT/dp ≈ −0.0075 K/MPa. Plot cutting speed against pressure, expecting proportionality if pressure melting dominates, though heat conduction through the wire matters too.",
   "slVsHl": "Mostly beyond SL. Even an HL student needs to be careful: the real effect of pressure is tiny, and heat flow from the room through the wire probably dominates. Top band work compares the predicted temperature shift with the speed and evaluates that heat conduction through the wire, not pressure alone, explains the result.",
   "whereMarksAreLost": "Research design: measuring melting point with a thermometer cannot detect a shift of a few hundredths of a kelvin. Conclusion: claiming pressure melting is confirmed when the wire is warmer than the ice. Evaluation: not testing a nylon thread for comparison.",
   "dataNote": "Needs a large clear ice block, a thin wire and steady room conditions; heat conduction along the wire is the hard uncertainty to remove.",
   "verdict": "Risky. The original idea of measuring a melting point shift with a thermometer cannot work, but the wire experiment is a real classic if you compare steel with nylon to test the explanation. Only choose it if you enjoy the conclusion being complicated."
  },
  {
   "id": "rubber-band-launch-range-at-different-starting-temperatures",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Rubber band launch range at different starting temperatures",
   "researchQuestion": "How does the temperature of a rubber band (5, 15, 25, 35, 45, 55 °C ± 1 °C) affect the horizontal range of a fixed-stretch launch, in m?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Band temperature, 6 values from about 5 °C (ice bath) to 55 °C (warm water bath), with 5 launches per temperature and a new band from the same pack for each.",
   "dependentVariable": "Horizontal range from a tape measure and, better, launch speed from a video in Tracker, allowing the kinetic energy ½mv² of a small projectile to be compared with the stretch energy.",
   "controlledVariables": "Stretch: fixed with a stop at the same length. Launch angle: set to 45° with a clamp jig. Projectile: same mass, e.g. a small foam pellet. Time out of the bath: 10 s before firing, dried, with temperature checked by a probe.",
   "physicsNeeded": "Elastic energy stored is related to the force-extension curve, and a rubber band gets stiffer when hot (the entropy effect), so the trend is not what many students predict. For a projectile, range R ∝ v², and v² is proportional to stored energy, so plot R against temperature to test the trend and explain it using kinetic theory of the polymer chains.",
   "slVsHl": "SL: measure R, and describe the change with temperature. Deeper: measure force at fixed extension with a newton meter at each temperature, which links to the stored energy, and discuss hysteresis and the cooling during the delay.",
   "whereMarksAreLost": "Research design: temperature changes during the transfer and is not measured at launch. Data analysis: different bands are not identical, so the spread is large. Conclusion: guessing that 'hot is stretchier' rather than looking at data. Evaluation: not testing wet against dry bands, or ageing of the rubber.",
   "dataNote": "Needs a water bath, thermometer and a launch jig; band variation and cooling before launch are the main uncertainties.",
   "verdict": "Interesting because the result may surprise you. The thermodynamics is only qualitative at school level, so add the force-extension measurement at each temperature to make it solid."
  },
  {
   "id": "water-volume-and-cooling-rate-in-moving-air",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "both",
   "title": "Water volume and cooling rate in moving air",
   "researchQuestion": "How does the volume of hot water, from 50 cm³ to 250 cm³ at a starting 70 °C, affect its initial cooling rate in a steady airflow of 2 m/s?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Volume of water in identical beakers, 50, 100, 150, 200, 250 cm³ (5 values), 3 repeats each.",
   "dependentVariable": "Temperature with a thermometer or probe every 30 s for 10 min, giving initial cooling rate in °C per s. Power lost is found from mcΔθ/Δt.",
   "controlledVariables": "Fan at a fixed distance and speed, checked with an anemometer. Same beaker shape, so the surface area changes only through depth. Same start temperature and room temperature. Lid on or off, decided and kept the same.",
   "physicsNeeded": "Energy loss Q = mcΔθ, and rate of loss depends on surface area and temperature difference, with evaporation adding to it. Plot cooling rate against 1/volume or 1/mass; a straight line through the origin suggests roughly constant power loss.",
   "slVsHl": "SL students can compare cooling rates and explain in terms of mass and surface area. Top band work separates evaporation from convection with a lid, and fits Newton's law of cooling to extract a constant for each volume.",
   "whereMarksAreLost": "Research design: airflow not uniform across the beaker, and evaporation ignored. Data analysis: using average rates over different temperature ranges. Conclusion: not linking the trend to power loss. Evaluation: not discussing that beaker walls and base also conduct.",
   "dataNote": "Beakers, a fan, an anemometer and a thermometer are enough; the main uncertainty is uneven airflow and evaporation.",
   "verdict": "Simple and safe, so the marks come from the analysis. Adding a lid comparison is the twist that makes it more than a routine cooling experiment."
  },
  {
   "id": "young-modulus-of-a-heated-copper-wire",
   "topic": "B.1",
   "topicName": "Thermal energy transfers",
   "level": "HL",
   "title": "Young modulus of a heated copper wire",
   "researchQuestion": "How does the temperature of a copper wire (20, 40, 60, 80, 100 °C) affect its measured Young modulus, in GPa, over an elastic extension of under 0.1%?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Wire temperature, 5 values from room temperature to about 100 °C, heated by passing a small current or by an enclosing hot water tube, with 3 repeated load series at each temperature.",
   "dependentVariable": "Extension for a range of loads, measured with a travelling microscope, a Vernier scale or a dial gauge. Stress and strain are calculated, and E is found as the gradient of stress against strain. Wire diameter is taken with a micrometer.",
   "controlledVariables": "Wire length and diameter: the same wire, measured with a metre rule and micrometer. Load range: kept within elastic behaviour. Thermal expansion: the reference length is corrected or a control wire is used. Time at temperature: allowed to settle for 3 minutes before each reading.",
   "physicsNeeded": "E = stress/strain = (F/A)/(ΔL/L). Plot stress against strain at each temperature, and the gradient is E. Then plot E against temperature. A drop of only a few percent over 80 K is expected, so uncertainty is a key issue. Thermal expansion of the wire is of a similar size to the elastic extension and needs correcting.",
   "slVsHl": "Mostly beyond SL because of the precision needed, but a strong SL student could do it with careful method. Top band: separating thermal expansion from load extension, propagating uncertainty in ΔL, and comparing the trend with the data book value.",
   "whereMarksAreLost": "Research design: thermal expansion mixes with the extension, and thin wires kink or yield. Data analysis: very small extensions (tens of micrometres) have a large percentage uncertainty. Conclusion: claiming a trend when the change is within error. Evaluation: temperature not uniform along the wire.",
   "dataNote": "Needs a long thin wire, precise extension measurement and safe heating; the extension resolution and uniform temperature are the main problems.",
   "verdict": "Hard and risky. The expected change is only a few percent, so most school setups cannot detect it. Only choose it if your school has a good optical or dial gauge system, and otherwise switch to a wire of different length or diameter at room temperature."
  },
  {
   "id": "solar-cell-output-power-against-tilt-angle-under-a-lamp",
   "topic": "B.2",
   "topicName": "Greenhouse effect",
   "level": "both",
   "title": "Solar cell output power against tilt angle under a lamp",
   "researchQuestion": "How does the maximum power output of a small silicon solar cell vary with tilt angle θ from 0° to 80° in 10° steps, under a lamp fixed 0.30 m from the cell centre?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Angle between the cell normal and the lamp direction, 0° to 80° in 10° steps (9 values), on a rotating protractor mount, 3 repeats each.",
   "dependentVariable": "Power P = VI at the maximum power point, found by varying a load resistor (10 Ω to 1 kΩ) with a voltmeter and ammeter. Compare with a cosθ model.",
   "controlledVariables": "Lamp distance to cell centre, measured by ruler at each angle. Lamp power, supplied from a stabilised source. Cell temperature, limited by a heat filter and short exposure times. Room lighting, blocked by a dark screen.",
   "physicsNeeded": "Intensity on a surface falls as I cosθ, so the power should be P = P0 cosθ. Plot P against cosθ and test for a straight line through the origin. Compare gradient with P0.",
   "slVsHl": "SL students test the cosine law. Top work looks at deviations at large angles due to reflection (Fresnel-like losses) and heat, and uses a lux meter to convert the power to efficiency.",
   "whereMarksAreLost": "Research design: allowing the lamp to heat the cell, which lowers voltage. Data analysis: using power at one fixed load and not the maximum power point. Evaluation: stray light at high angles.",
   "dataNote": "Needs a lamp, small cell, load box and two meters; the main uncertainty is angle setting, about ±2°, and heating.",
   "verdict": "Very common, so make it yours by finding the true maximum power point at every angle and explaining why the data leave the cosine curve at large angles."
  },
  {
   "id": "surface-finish-and-lamp-heated-plate-temperature",
   "topic": "B.2",
   "topicName": "Greenhouse effect",
   "level": "both",
   "title": "Surface finish and lamp-heated plate temperature",
   "researchQuestion": "How does the reflectance of a metal plate's coating, varied from about 0.1 to 0.9 using different paper or paint finishes, affect its equilibrium temperature under a 60 W lamp held 20 cm away?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Surface reflectance: 6 finishes from matt black to white to polished foil, each one measured independently using a light sensor comparing reflected and incident light (about 0.1 to 0.9).",
   "dependentVariable": "Equilibrium temperature of the plate, found with a thermocouple taped to the back (±0.1 °C) and logged until it stops rising, about 15 to 20 minutes. Repeat 3 times.",
   "controlledVariables": "Distance and angle from lamp: fixed with a clamp and a ruler. Plate: same aluminium sheet with a coating on the front only. Room temperature: measured and starting with the plate at the same value. Back of plate: insulated with foam.",
   "physicsNeeded": "At equilibrium, absorbed power (1 − a) I A equals power lost by convection and radiation, roughly h A (T − T_room). Plot (T − T_room) against (1 − a): expected straight line through the origin if heat loss is linear. The gradient links to intensity over the loss coefficient.",
   "slVsHl": "SL: plot temperature rise against measured absorbed fraction. Top band or HL depth: relate to the Stefan-Boltzmann law and the fact that the lamp emits mostly infrared, so visible colour is not a reliable measure of absorption.",
   "whereMarksAreLost": "Research design: judging reflectivity by colour by eye instead of measuring it. Data analysis: not using the temperature rise above the room. Conclusion: ignoring that a lamp's infrared differs from visible light. Evaluation: not commenting on the emissivity of the coating, which also changes the losses.",
   "dataNote": "Needs a thermocouple or probe and a light meter; the main uncertainty is that visible reflectance does not equal infrared absorption and that the lamp warms the air.",
   "verdict": "Good link to the greenhouse and albedo theme, but only if you measure reflectance yourself. The twist of comparing visible and infrared behaviour is what makes it worth choosing."
  },
  {
   "id": "temperature-rise-of-coloured-cans-under-a-lamp",
   "topic": "B.2",
   "topicName": "Greenhouse effect",
   "level": "both",
   "title": "Temperature rise of coloured cans under a lamp",
   "researchQuestion": "How does the initial rate of temperature rise of 100 mL of water in aluminium cans covered with different colours of paper, from white to black, change under a 100 W lamp at 20 cm?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Colour of the covering, 6 to 8 colours or grey levels from white to black, each repeated 3 times.",
   "dependentVariable": "Water temperature with a probe every 30 s for 10 minutes; initial rate from the gradient of T against t; a light meter can give the reflectance.",
   "controlledVariables": "Distance from lamp fixed with a clamp. Same starting water temperature, about room temperature. Same can and paper thickness, with matte paper only. Room darkened with no other light source.",
   "physicsNeeded": "Absorbed power P = (1 - albedo) x intensity x area, and rate of temperature rise = P/(mc). Plot initial heating rate against reflectance from a light meter; the line should be straight and decreasing, showing absorption depends on the reflected fraction.",
   "slVsHl": "SL: rate against colour or grey level with uncertainties. Top band: quantify reflectance with a light meter and check the linear relationship. HL: consider the emission of the can and the lamp spectrum, including infrared, which colour does not test.",
   "whereMarksAreLost": "Research design: lamp distance and starting temperature vary. Data analysis: colours not ranked on a scale. Conclusion: no link to reflectance. Evaluation: ignoring that visible colour may not predict infrared absorption.",
   "dataNote": "Needs cans, a lamp, a temperature probe and paper; the main uncertainty is heating from the lamp changing during the run.",
   "verdict": "Easy but commonplace, so build a quantitative scale. Twist by measuring reflectance with a light meter and comparing visible and infrared behaviour with a thermal camera or a filter."
  },
  {
   "id": "testing-inverse-square-fall-off-for-a-bulb-and-a-torch",
   "topic": "B.2",
   "topicName": "Greenhouse effect",
   "level": "both",
   "title": "Testing inverse square fall-off for a bulb and a torch",
   "researchQuestion": "How does the illuminance measured by a light sensor change with distance from a small filament bulb and from a lens-focused torch, for distances from 0.20 m to 1.00 m in steps of 0.10 m?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Distance from source to sensor, 0.20 to 1.00 m in 9 steps, measured with a metre rule fixed on an optical bench; three readings at each distance. Two sources: bare bulb and torch with reflector.",
   "dependentVariable": "Illuminance in lux from a light sensor or lux meter, with the background reading in a darkened room subtracted; the calculated quantity is the exponent n in I = k/d^n.",
   "controlledVariables": "Supply voltage to the bulb held with a stabilised power supply and checked on a voltmeter. Room darkness kept constant by blinds and a black cloth. Sensor orientation kept normal to the source using a fixed mount. Warm-up time of 2 minutes before every run.",
   "physicsNeeded": "For a point source I = P/(4πd²). Plot ln I against ln d: the gradient should be -2 for the bulb and different for the torch. Alternatively plot I against 1/d². Correct for the sensor and the bulb not being a true point by measuring from the filament position.",
   "slVsHl": "SL students compare the two gradients and comment on the shape of the graphs. Top band work adds a distance offset as a fitted parameter, uncertainty on the gradient from a worst-fit line, and a reasoned range over which the point approximation is valid. Note this is really a light intensity topic, so the syllabus link is weak: the inverse square law is best framed as an analogy to field strength.",
   "whereMarksAreLost": "Research design: no treatment of stray light, and a weak syllabus link. Data analysis: distance uncertainty ignored when the filament position is unclear. Conclusion: claiming n = 2 exactly without comparing to the gradient uncertainty. Evaluation: not discussing the finite size of the bulb at short distances.",
   "dataNote": "Needs a lux meter or light sensor and a bench; the main uncertainty is stray light and the unknown position of the filament.",
   "verdict": "Easy to run but common and only loosely tied to the syllabus, so the twist matters. Add the torch comparison and fit the offset to make it yours."
  },
  {
   "id": "boyle-s-law-with-a-syringe-and-dead-volume",
   "topic": "B.3",
   "topicName": "Gas laws",
   "level": "both",
   "title": "Boyle's law with a syringe and dead volume",
   "researchQuestion": "How does the pressure of air trapped in a syringe vary as its volume is reduced from 50 cm³ to 20 cm³, and what dead volume in the tubing does the fit give?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Syringe reading from 50 cm³ down to 20 cm³ in 5 cm³ steps, giving seven values, and each compressed and released three times.",
   "dependentVariable": "Pressure from a digital gas pressure sensor or a Bourdon gauge, in kPa. Calculate 1/(V + V0) and fit for the dead volume V0.",
   "controlledVariables": "Temperature held constant by moving the plunger slowly and waiting 30 s at each reading. Same amount of trapped air with no leaks, checked by holding a reading. Syringe lubricated with a drop of silicone oil. Same sensor tubing length.",
   "physicsNeeded": "pV = constant at fixed T and amount of gas, and with dead volume p(V + V0) = k. Plot 1/p against V; the intercept on the V axis is −V0 and the gradient is 1/k.",
   "slVsHl": "SL verifies inverse proportionality with a straight line. Stronger work fits the dead volume V0 and shows the uncorrected graph does not pass through the origin. HL depth could explore adiabatic effects by pushing quickly and estimating the heating.",
   "whereMarksAreLost": "Data analysis: plotting p against V and calling the curve inverse without a linearised graph. Evaluation: ignoring dead volume, leaks and friction in the plunger. Conclusion: claiming the law is verified when the graph intercept is not zero.",
   "dataNote": "Needs a syringe and a pressure sensor; the main uncertainty is the unknown volume in the connector and slow leaks.",
   "verdict": "A standard experiment, so it needs the dead volume analysis to be worth doing. Twist: compare slow and fast compression to show isothermal versus adiabatic behaviour."
  },
  {
   "id": "counting-molecules-of-air-in-a-syringe-from-p-v-and-t",
   "topic": "B.3",
   "topicName": "Gas laws",
   "level": "both",
   "title": "Counting molecules of air in a syringe from p, V and T",
   "researchQuestion": "How closely does the number of air molecules calculated from pV = nRT match the number expected from the mass of air in a 60 cm³ syringe, at gas volumes of 20 to 60 cm³ in 5 steps?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Trapped air volume, six values from 20 to 60 cm³ at room temperature, set with a syringe connected to a pressure sensor.",
   "dependentVariable": "Pressure from a digital pressure sensor in kPa. Calculate n = pV/RT, then N = n·N_A. Compare with N from the air mass measured on a 0.001 g balance by weighing the sealed syringe empty and full, or from repeated volume readings.",
   "controlledVariables": "Temperature kept constant by compressing slowly and waiting 30 seconds and recording room temperature. Same amount of air sealed each run, with no leaks checked by holding the plunger. Same syringe and sensor with dead volume in the tube measured.",
   "physicsNeeded": "pV = nRT and N = nN_A. Plot p against 1/V, gradient = nRT. From the gradient calculate n, then the number of particles N. Compare with N from mass, m/M·N_A, using air M = 29 g/mol.",
   "slVsHl": "SL students can obtain n from the gradient of p against 1/V with uncertainty. For higher marks, include the tube dead volume as the intercept on a V + V₀ axis. HL work could use Boltzmann's constant with pV = NkT to get N directly.",
   "whereMarksAreLost": "Research design: 'verify Avogadro's number' as the aim, which is not achievable from one gas sample. Data analysis: ignoring the dead volume in the connection. Evaluation: not discussing heating during compression.",
   "dataNote": "Needs a syringe and pressure sensor; the dead volume and slow leaks are the dominant uncertainties.",
   "verdict": "Fine if the RQ is about agreement between two independent estimates of N and not about proving Avogadro. Twist: compare air with a sample of your own breath."
  },
  {
   "id": "measuring-the-gas-constant-with-a-syringe-and-water-bath",
   "topic": "B.3",
   "topicName": "Gas laws",
   "level": "both",
   "title": "Measuring the gas constant with a syringe and water bath",
   "researchQuestion": "What value of the molar gas constant R is obtained from a fixed sample of air in a sealed syringe heated from 20 °C to 80 °C, and how close is it to 8.31 J mol⁻¹ K⁻¹?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Temperature of the air sample, 20, 30, 40, 50, 60, 70, 80 °C (7 values) in a water bath, with 3 repeats per value. Pressure is held near atmospheric.",
   "dependentVariable": "Volume of air read from the syringe scale. Amount of gas is found from the initial state, and R is found from the gradient of V against T.",
   "controlledVariables": "Pressure kept constant with a freely moving, lubricated syringe. Amount of gas fixed by sealing the outlet. Thermal equilibrium allowed for 3 min at each step. Atmospheric pressure recorded from a barometer.",
   "physicsNeeded": "pV = nRT, so at constant pressure V = (nR/p)T. Plot V against T in kelvin; the gradient equals nR/p, so R = gradient × p/n. Dead volume in the tip appears as an intercept.",
   "slVsHl": "SL students calculate R from the gradient and compare with the accepted value. Top band work corrects for dead volume and friction, propagates uncertainty from n and p, and comments on systematic offset.",
   "whereMarksAreLost": "Research design: not finding the amount of gas properly. Data analysis: using Celsius on the axis, or forgetting dead volume. Conclusion: comparing to the accepted value without judging whether the difference is within uncertainty. Evaluation: not testing syringe friction or heat loss from the exposed part.",
   "dataNote": "Glass or plastic syringe, water bath and thermometer; the main uncertainty is friction of the plunger and the amount of gas.",
   "verdict": "Very doable and gives a numerical target. Do not just repeat it; fit V against T and interpret the intercept to give the analysis real depth."
  },
  {
   "id": "pressure-of-trapped-air-in-water-baths-and-absolute-zero",
   "topic": "B.3",
   "topicName": "Gas laws",
   "level": "both",
   "title": "Pressure of trapped air in water baths and absolute zero",
   "researchQuestion": "How does the pressure of a fixed mass of air at constant volume change as its temperature is raised from 0 °C to 90 °C in steps of 10 °C, and what value of absolute zero does the extrapolation give?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Bath temperature: 0 °C (ice water), then about 20, 30, 40, 50, 60, 70, 80, 90 °C (at least 6 values), each measured with a thermometer at the flask (±0.5 °C). Three readings each while heating and cooling.",
   "dependentVariable": "Pressure of air in a sealed flask read from a pressure sensor or Bourdon gauge (±0.5 kPa). Absolute zero is found from where the extrapolated line meets P = 0.",
   "controlledVariables": "Gas amount: flask sealed once with a bung and no leaks. Volume: rigid flask, with tubing volume kept small. Time at each temperature: wait 3 minutes for thermal equilibrium, with stirring. Immersion: the whole flask below the water surface.",
   "physicsNeeded": "P/T = constant at fixed V, so P = kT_C + P₀ with T in °C. Plot P against θ (°C): x-intercept at −P₀/k gives absolute zero, about −273 °C. Compare and calculate a percentage difference.",
   "slVsHl": "SL: plot the graph, extrapolate and compare with −273 °C. Top band or HL depth: use the maximum and minimum gradient lines for the uncertainty on the intercept, and estimate the effect of the connecting tube being at room temperature.",
   "whereMarksAreLost": "Research design: leaks and the dead volume of the sensor tube. Data analysis: a very long extrapolation with no uncertainty on the result. Conclusion: not checking whether the result is within the uncertainty range. Evaluation: not addressing the gas not being at the bath temperature.",
   "dataNote": "A pressure sensor with a flask and bung is needed; the main uncertainty is a long extrapolation and the gas in the tubing not being at the bath temperature.",
   "verdict": "A classic and often seen, so the personal twist has to come from the analysis, for example the uncertainty of the extrapolated intercept and the dead volume correction. Safe and dependable data."
  },
  {
   "id": "simulated-gas-temperature-and-wall-collision-frequency",
   "topic": "B.3",
   "topicName": "Gas laws",
   "level": "both",
   "title": "Simulated gas temperature and wall collision frequency",
   "researchQuestion": "How does the temperature of a simulated ideal gas of 200 particles, varied from 100 K to 500 K, affect the number of wall collisions per second in a fixed box?",
   "dataDifficulty": 1,
   "dataSource": "simulation",
   "sitesListingIt": 1,
   "independentVariable": "Gas temperature in a particle simulation, 100, 200, 300, 400, 500 K (5 values), with 5 runs per value using different random starts.",
   "dependentVariable": "Collisions with the walls per second counted by the simulation for a fixed 10 s run. Mean speed and pressure are also recorded and compared with prediction.",
   "controlledVariables": "Number of particles fixed. Box volume fixed. Particle mass and size identical. Run duration and time step the same.",
   "physicsNeeded": "Average speed scales as √T, so collision rate should be proportional to √T at fixed volume and particle number. Plot collision rate against √T; the gradient depends on particle number and box size. Compare with pressure proportional to T.",
   "slVsHl": "SL students record collision rates and link them to kinetic theory. Top band work derives the expected √T law, tests it, and discusses how the simulation's finite particle size and time step limit agreement.",
   "whereMarksAreLost": "Research design: a simulation with no justification of settings. Data analysis: treating random variation as if it were a real uncertainty. Conclusion: not testing the √T prediction. Evaluation: not discussing model assumptions such as no intermolecular forces.",
   "dataNote": "PhET Gas Properties or a short Python script; the main uncertainty is statistical scatter and what the simulation actually counts.",
   "verdict": "Acceptable but thin as a pure simulation. Writing your own short Python model makes it personal and gives you far more control over the variables."
  },
  {
   "id": "speed-of-sound-in-air-from-5-to-50-c",
   "topic": "B.3",
   "topicName": "Gas laws",
   "level": "both",
   "title": "Speed of sound in air from 5 to 50 °C",
   "researchQuestion": "How does the speed of sound in air in a closed tube vary with air temperature from 10 °C to 50 °C in seven steps, and does the gradient of v² against T match the ideal-gas value?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Air temperature in the tube: about 10, 20, 25, 30, 35, 40, 50 °C (seven values), reached by warming the tube with a water jacket or hairdryer and cooling.",
   "dependentVariable": "Speed of sound, from resonance frequency in a closed tube of known length (v = 4Lf, with end correction) using a speaker and a microphone; temperature read with a digital thermometer inside the tube.",
   "controlledVariables": "Tube length (measured at each temperature, checking expansion is negligible); humidity (same air, tube dry); speaker and microphone positions; mode of resonance (always the first).",
   "physicsNeeded": "v = √(γRT/M), so v² is proportional to T in kelvin. Plot v² against T (K): gradient γR/M, about 402 m²s⁻²K⁻¹ for dry air. Compare the experimental gradient with this.",
   "slVsHl": "SL can plot v against T and compare with the theory. Top-band work fits v² against T, includes the intercept, and discusses the effect of humidity. HL students can derive v from kinetic theory.",
   "whereMarksAreLost": "Research design: temperature gradient along the tube, so the reading does not represent the air. Data analysis: forgetting to convert to kelvin. Evaluation: neglecting humidity and the end correction.",
   "dataNote": "Tube, water bath or heater, thermometer and speaker with a microphone; the main uncertainty is non-uniform air temperature in the tube.",
   "verdict": "Interesting because it links waves and gases, but temperature control is the difficulty. Let the air settle for a few minutes before each reading and record the temperature at both ends."
  },
  {
   "id": "volume-of-trapped-air-against-temperature-at-constant-pressure",
   "topic": "B.3",
   "topicName": "Gas laws",
   "level": "both",
   "title": "Volume of trapped air against temperature at constant pressure",
   "researchQuestion": "How does the volume of a fixed sample of air trapped by a mercury-free oil plug or a syringe vary as the temperature is raised from 20 C to 80 C in 10 C steps?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Water bath temperature, 7 values from 20 C to 80 C, with each set repeated 3 times.",
   "dependentVariable": "Length of the air column in a capillary tube, or syringe reading, with a ruler; volume from cross-sectional area; temperature measured with a digital probe.",
   "controlledVariables": "Pressure kept at atmospheric with a free moving oil plug. Same mass of air, tube sealed at one end. Wait at least 3 minutes for thermal equilibrium at each step. Tube fully submerged to the same depth.",
   "physicsNeeded": "Charles's law V proportional to T with temperature in kelvin. Plot V against T in kelvin; the line passes through the origin, and extrapolating V against T in Celsius gives absolute zero as an x-intercept near -273 C.",
   "slVsHl": "SL: linear graph and absolute zero estimate with uncertainty. Top band: assess systematic effects such as air heating unevenly, and compare the estimate with the accepted value. HL: link to kinetic theory and the ideal gas equation.",
   "whereMarksAreLost": "Research design: not waiting for equilibrium. Data analysis: extrapolation with no uncertainty range. Conclusion: not comparing intercept with -273 C. Evaluation: ignoring the dead volume in the syringe or moisture in the tube.",
   "dataNote": "Needs a capillary tube and water bath or a syringe with a thermometer; the main uncertainty is temperature difference between bath and gas.",
   "verdict": "Classic and quite common in schools, so depth is what wins marks. Twist by using the extrapolation to absolute zero and analysing what the systematic error in your intercept is."
  },
  {
   "id": "syringe-compression-speed-isothermal-or-adiabatic",
   "topic": "B.4",
   "topicName": "Thermodynamics",
   "level": "HL",
   "title": "Syringe compression speed: isothermal or adiabatic",
   "researchQuestion": "How does the time taken to compress air in a 60 ml syringe from 60 ml to 20 ml, varied from 0.2 s to 20 s, affect the effective exponent γ in PV^γ = constant?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Compression time: 6 values from about 0.2 s to 20 s, timed with a data logger and driven by a falling mass or a hand pressed against a ruler. Three repeats each.",
   "dependentVariable": "Pressure from a fast pressure sensor connected to the syringe, logged at 100 Hz, with volume from the plunger position on the scale. The exponent is the gradient of ln P against ln V.",
   "controlledVariables": "Starting amount of air: same 60 ml at room pressure and temperature. Compression ratio: same in every trial. Syringe: same smooth syringe with a seal, tested for leaks. Rest time: wait 2 minutes between trials so the gas returns to room temperature.",
   "physicsNeeded": "Isothermal: PV = constant, so γ_eff = 1. Adiabatic: PV^γ = constant with γ = 1.4 for air. Plot ln P against ln V: gradient is −γ_eff. Then plot γ_eff against log of compression time.",
   "slVsHl": "HL: adiabatic processes are HL syllabus, so it fits HL best. Top band: model the thermal time constant of the syringe wall and explain why even the fast run does not reach 1.4.",
   "whereMarksAreLost": "Research design: no way to measure volume at the same moment as the pressure. Data analysis: pressure logged without synchronisation with the volume. Conclusion: not comparing with both limiting cases. Evaluation: friction, leaks and dead volume in the sensor tube.",
   "dataNote": "Needs a fast pressure sensor and a way to record plunger position, for example video analysis; the main uncertainty is dead volume and friction.",
   "verdict": "Interesting and truly HL, but difficult to get clean data. Choose it only if you have a fast sensor; video of the scale is a practical way to get volume."
  },
  {
   "id": "temperature-coefficient-of-resistance-of-a-metal-wire",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Temperature coefficient of resistance of a metal wire",
   "researchQuestion": "How does the resistance of a 1.0 m length of 0.20 mm enamelled copper wire change with temperature between 20 °C and 90 °C in a stirred water bath, and what temperature coefficient of resistance follows?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 4,
   "independentVariable": "Bath temperature, 20 to 90 °C in 10 °C steps (8 values), each repeated 3 times on both heating and cooling.",
   "dependentVariable": "Resistance from a four-wire measurement: voltmeter p.d. divided by ammeter current, or a digital multimeter in resistance mode. Bath temperature is read with a digital thermometer. Resistivity is calculated from R, length and diameter (micrometer).",
   "controlledVariables": "Current kept small (about 0.1 A, checked with a rheostat) so the wire is not self-heated. Wire length and diameter fixed by using one coiled sample. Thermal equilibrium ensured by stirring and waiting 2 minutes before each reading. Same meters and leads throughout.",
   "physicsNeeded": "R = ρL/A and, for a metal, R ≈ R0(1 + αΔT). Plot R against θ in °C. The gradient is R0α and the intercept gives R0, so α = gradient divided by intercept. Check the straight line is linear and compare α with the accepted value near 0.004 per kelvin.",
   "slVsHl": "SL students get a clean linear graph and a value of α with uncertainty. To reach the top band, add a second material such as nichrome or a thermistor, use a four-wire method to remove lead resistance, and discuss why the fit is or is not linear. HL adds nothing syllabus-specific, but the microscopic link to lattice vibrations can strengthen the conclusion.",
   "whereMarksAreLost": "Research design: wire self-heating and thermometer not measuring the wire's real temperature. Data analysis: ignoring uncertainty in small resistances (copper changes only about 30% over the range). Conclusion: no comparison with literature α. Evaluation: not naming lead resistance or thermal lag as systematic errors.",
   "dataNote": "Needs a water bath, thermometer and a precise multimeter; the main uncertainty is that the wire lags behind the bath thermometer and the resistance change is small.",
   "verdict": "Very common (listed on 4+ sites), so it only stands out if you add a second material or the four-wire method. Worth choosing if you like electrical measurement and want a reliable linear graph."
  },
  {
   "id": "cold-and-warm-effects-on-a-aa-cell-s-internal-resistance",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Cold and warm effects on a AA cell's internal resistance",
   "researchQuestion": "How does the internal resistance r of an alkaline AA cell change as its temperature is varied from 5 °C to 55 °C in steps of 10 °C?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 3,
   "independentVariable": "Cell temperature, 5, 15, 25, 35, 45, 55 °C, held in a water bath and left for 10 minutes each, with three cells or repeats.",
   "dependentVariable": "Terminal voltage V and current I across 4 to 6 load resistances from 2 Ω to 20 Ω with a digital multimeter and an ammeter. r is the negative of the gradient of a V against I graph at each temperature.",
   "controlledVariables": "Same brand and batch of cell, ideally fresh for each temperature. Same set of resistors. Circuit closed only briefly to avoid drain and self-heating. Cell sealed in a bag so it stays dry. Same meters.",
   "physicsNeeded": "ε = V + Ir, so V = ε − Ir. Plot V (y) against I (x) at each temperature. The gradient is −r and the intercept is ε. Then plot r (y) against T (x) to look for the trend.",
   "slVsHl": "SL students can produce V against I lines and a plot of r against T. To reach top band, use gradient uncertainties and justify the range. HL students can link to reaction kinetics and fit an exponential in 1/T.",
   "whereMarksAreLost": "Research design: cell drained by long measurement, so r rises for reasons other than temperature. Data analysis: uncertainty in r from a single reading rather than a gradient. Conclusion: not comparing with the temperature. Evaluation: cell temperature not checked at the moment of measurement.",
   "dataNote": "Needs a water bath, thermometer, meters and a set of resistors, and the largest uncertainty is battery drain and the cell cooling during measurement. Keep it to AA cells and avoid heating high, and never heat any lithium cell.",
   "verdict": "A good idea with a clear physical trend, and it is well within reach. The twist is to separate temperature from discharge, for example by keeping each run short and using fresh cells. Keep the safety plan clear."
  },
  {
   "id": "current-voltage-curves-of-a-solar-cell-at-varied-irradiance",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Current voltage curves of a solar cell at varied irradiance",
   "researchQuestion": "How do the short circuit current and maximum power of a small solar panel change as irradiance is varied from 50 to 400 W m⁻² in about 8 steps?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 3,
   "independentVariable": "Irradiance at the panel, changed by moving a lamp from 15 to 60 cm, or by using filters. Measured directly by a lux meter or calibrated solar power meter, 8 values, each measured three times.",
   "dependentVariable": "Current and voltage from a variable load resistor box (10 Ω to 1 kΩ) with two multimeters. Draw the I-V curve for each irradiance to find Isc, Voc and the maximum of P = VI.",
   "controlledVariables": "Panel orientation, perpendicular to the beam. Same lamp, with warm up time. Panel temperature, using a fan or short readings. Room darkened to remove stray light.",
   "physicsNeeded": "Isc is proportional to irradiance, and Voc increases logarithmically. Plot Isc (y) against irradiance (x) for a straight line, and Pmax against irradiance. Do not use 1/d² as the independent variable unless the lamp is shown to be a point source; measure the irradiance instead.",
   "slVsHl": "SL students can produce I-V curves and Pmax against irradiance. Top band work gives efficiency as Pmax over irradiance times area and discusses the fill factor. HL adds nothing needed.",
   "whereMarksAreLost": "Research design: assuming inverse square for a lamp close to the panel, and no check of temperature. Data analysis: only using one resistor value, so the maximum power point is missed. Conclusion: not commenting on linearity. Evaluation: heating of panel, spectrum of the lamp and stray light.",
   "dataNote": "A small panel, a resistance box, two meters and a lux meter; the main uncertainty is the lux meter conversion to W m⁻² and lamp heating.",
   "verdict": "Good and practical with plenty of data, and popular so you need the full I-V curve to stand out. Twist: compare efficiency with sunlight outdoors on a clear day."
  },
  {
   "id": "forward-voltage-drop-of-a-diode-against-temperature",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Forward voltage drop of a diode against temperature",
   "researchQuestion": "How does the forward voltage of a silicon diode at a constant 5.0 mA change as its temperature is raised from 20 °C to 80 °C in 10 °C steps?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Diode temperature, 20 °C to 80 °C, in 10 °C steps (7 values), with the diode in a water bath or oil bath and a thermometer next to it. Repeat on heating and cooling.",
   "dependentVariable": "Voltage across the diode measured with a digital multimeter at a fixed current. Optionally the rectified output of a bridge across a load, and efficiency as output power over input power.",
   "controlledVariables": "Forward current, set with a resistor and a supply and rechecked at each temperature. Same diode. Waterproofed leads. Load resistance if a bridge is used. Time allowed for temperature equilibrium.",
   "physicsNeeded": "Diode forward voltage falls with temperature at about −2 mV K⁻¹. Plot V (y) against T (x). The gradient is about −2 mV K⁻¹ and can be compared with the literature. Efficiency of a bridge rectifier can be linked to the two diode drops.",
   "slVsHl": "SL students can measure V against T and give the gradient. The topic as supplied, efficiency of the rectifier, is vague, so restrict it to the forward voltage first, then extend to efficiency. A deeper analysis uses the Shockley equation, which goes beyond the syllabus.",
   "whereMarksAreLost": "Research design: the original efficiency question is not clearly measurable and the current is allowed to drift. Data analysis: thermometer lag ignored. Conclusion: unclear link between voltage drop and efficiency. Evaluation: self heating and non uniform temperature not discussed.",
   "dataNote": "Multimeter, resistor and water bath are enough; the main uncertainty is that the thermometer and diode may not be at the same temperature.",
   "verdict": "Interesting and a bit different, but only worth it if you narrow it to the forward voltage. Twist: repeat with a germanium and an LED for comparison."
  },
  {
   "id": "ntc-thermistor-beta-parameter-from-a-water-bath",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "NTC thermistor Beta parameter from a water bath",
   "researchQuestion": "How well does the resistance of an NTC thermistor between 10 °C and 80 °C follow R = R0 exp(B(1/T − 1/T0)), and what value of B results?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Water bath temperature from about 10 °C to 80 °C in 8 to 10 steps of roughly 7 °C, each set three times (once on heating, once on cooling, one more heating run).",
   "dependentVariable": "Resistance of the thermistor measured with a digital multimeter on the ohmmeter setting, or from V and I with a small current. Calculate ln R and 1/T in kelvin.",
   "controlledVariables": "Measuring current kept small (about 100 µA) so self-heating is negligible. Water stirred continuously and the reading taken only after 60 s of steady temperature. Same thermistor and same probe position next to the bead. Same leads and connections throughout.",
   "physicsNeeded": "For an NTC thermistor R = R0 exp(B/T) approximately, so ln R against 1/T (in K) is a straight line. The gradient equals B in kelvin. Residual plot shows whether the simple model holds across the range.",
   "slVsHl": "SL can find B and check linearity. Top band work compares B found from low and high halves of the range, tests for self-heating by changing current, and discusses why B is not truly constant. HL adds semiconductor band-gap link, since B = Eg/2k.",
   "whereMarksAreLost": "Data analysis: using °C instead of kelvin in the linearisation. Evaluation: thermometer and thermistor not at the same temperature because the water is not stirred, and ignoring self-heating. Research design: too few temperatures at the low end where R changes fastest.",
   "dataNote": "Needs a thermistor, beaker, kettle, ice, thermometer or temperature probe and a multimeter; main uncertainty is thermal lag between probe and thermistor.",
   "verdict": "A safe, clean choice that gives excellent graphs. Make it yours by using the band-gap link to estimate Eg and comparing it with a published value, or by turning your calibrated thermistor into a thermometer and testing it."
  },
  {
   "id": "resistance-of-nichrome-wire-against-length",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Resistance of nichrome wire against length",
   "researchQuestion": "How does the length of 0.28 mm diameter nichrome wire (0.10 to 0.80 m, 8 lengths) affect its resistance, measured using a voltage and current method?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Wire length, 0.10 to 0.80 m in 0.10 m steps, with a crocodile clip on a taped metre rule; 3 repeats each.",
   "dependentVariable": "Potential difference by voltmeter and current by ammeter, then R = V/I. Use low current, kept below 0.5 A.",
   "controlledVariables": "Same wire so material and diameter are fixed (check with a micrometer at several points). Current kept low and switched off between readings to limit heating. Same contact pressure at the clip. Room temperature noted.",
   "physicsNeeded": "R = ρL/A. Plot R against L; the gradient is ρ/A, so ρ = gradient × πd²/4, to compare with the tabulated value for nichrome.",
   "slVsHl": "SL work plots R against L and finds ρ. Top band handles the contact resistance intercept and the heating and quantifies the diameter uncertainty, since it is squared.",
   "whereMarksAreLost": "Research design: heating changing the resistance. Data analysis: ignoring the diameter uncertainty in ρ. Evaluation: clip contact resistance shown by the non-zero intercept.",
   "dataNote": "Standard kit with a power supply, meters and micrometer; the main uncertainty is diameter and contact resistance.",
   "verdict": "Extremely overdone, so it needs a real twist. Consider measuring the same wire at several temperatures in a water bath, or finding ρ and comparing it with a database value."
  },
  {
   "id": "time-constant-of-a-discharging-capacitor-against-resistance",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Time constant of a discharging capacitor against resistance",
   "researchQuestion": "How does the resistance (10 kΩ to 100 kΩ, 8 values) in series with a 100 µF capacitor affect the time constant found from its discharge curve?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Resistance, 10, 20, 30, 40, 50, 60, 80 and 100 kΩ, using 1% resistors checked with a multimeter. Three discharges per value.",
   "dependentVariable": "Capacitor voltage against time from a data logger or voltmeter with video at 1 Hz or faster. Time constant from the gradient of ln V against t, or by an exponential fit.",
   "controlledVariables": "Capacitance, using the same capacitor and measuring it. Initial voltage, e.g. 6.0 V, charged for the same time. Voltmeter of high input resistance, so it does not discharge the capacitor. Temperature, fully discharging between runs.",
   "physicsNeeded": "V = V₀e^(−t/RC). Plot ln V against t, with gradient −1/RC. Then plot τ (y) against R (x) for a line through the origin whose gradient is C. Compare with the labelled capacitance and its tolerance, often 20%.",
   "slVsHl": "SL students can find τ for each R and plot τ against R. For higher marks, consider the meter's internal resistance and the capacitor tolerance, and measure C separately. HL students can extend to charging curves and energy stored.",
   "whereMarksAreLost": "Research design: time constants too short to log by hand. Data analysis: fitting after the voltage reaches the noise level, no uncertainties in τ. Conclusion: not comparing the gradient with C. Evaluation: leakage current in electrolytic capacitors, and meter resistance in parallel.",
   "dataNote": "A capacitor, resistors, a power supply and a logger or a phone video; the main uncertainty is capacitor tolerance and meter loading.",
   "verdict": "A solid, reliable choice with good data, but standard, so the analysis must carry it. Twist: use the gradient to measure an unknown capacitor or find the input resistance of your own voltmeter."
  },
  {
   "id": "capacitor-charging-voltage-against-energy-released",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Capacitor charging voltage against energy released",
   "researchQuestion": "How does the charging voltage of a 4700 μF capacitor (2 to 12 V in 2 V steps) affect the energy delivered as it lifts a small mass?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Charging voltage, 2 to 12 V in six steps, 5 repeats each, set from a variable power supply and confirmed with a voltmeter.",
   "dependentVariable": "Energy delivered, found from the height a small motor lifts a known mass (metre rule), compared with ½CV²; alternatively integrate the current from a data logger.",
   "controlledVariables": "Same capacitor, discharged fully between runs; same motor and load mass; same wiring and connection resistance; same room temperature.",
   "physicsNeeded": "E = ½CV². Plot energy against V², which gives a line through the origin with gradient ½C. Compare the gradient to the marked capacitance, and estimate efficiency of the motor.",
   "slVsHl": "SL: energy against V² graph and comparison with C. Top band: split losses in the motor and connections, and measure C independently by charge–discharge with a resistor.",
   "whereMarksAreLost": "Research design: energy is only calculated from the formula, not measured. Data analysis: the ±20% tolerance of the capacitor is ignored. Conclusion: agreement claimed despite unexplained gradient difference.",
   "dataNote": "Needs a capacitor, supply, voltmeter and small motor; the main uncertainty is the capacitor tolerance and energy lost in the motor.",
   "verdict": "Only worth it if energy is measured rather than calculated. The lifted mass method gives you real data to defend."
  },
  {
   "id": "cell-temperature-and-open-circuit-voltage-of-a-solar-cell",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Cell temperature and open-circuit voltage of a solar cell",
   "researchQuestion": "How does the temperature of a silicon solar cell, from 15 °C to 65 °C in 10 °C steps, affect its open-circuit voltage under constant illumination?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Cell temperature from 15 °C to 65 °C, in 6 steps, each repeated 3 times. Warm the cell on a hotplate-heated aluminium block or with a water bath below it, and cool it with ice.",
   "dependentVariable": "Open-circuit voltage read with a multimeter, and cell temperature read with a thermocouple or digital thermometer glued to the back. Gradient dV/dT in mV per °C is found from a graph.",
   "controlledVariables": "Light intensity kept constant with a fixed LED or lamp and monitored with a light sensor; distance and angle fixed; readings taken quickly so the lamp does not add heat; cell shielded from stray light.",
   "physicsNeeded": "Open-circuit voltage falls almost linearly with temperature because the band gap narrows and the reverse saturation current rises; typically about −2 mV per °C per cell. Plot V_oc against T; the gradient gives the temperature coefficient to compare with literature.",
   "slVsHl": "An SL student can plot a straight line and compare the gradient with a datasheet. Top band work explains the trend in terms of semiconductor physics and also checks the effect on power at maximum power point.",
   "whereMarksAreLost": "Research design: lamp intensity changes as it heats, so temperature is not the only variable. Data analysis: temperature measured at the cell surface rather than the junction. Evaluation: uneven heating and thermal lag between the thermometer and cell.",
   "dataNote": "Needs a solar cell, multimeter, thermometer and a heat source; the main uncertainty is thermal lag, so wait for readings to settle.",
   "verdict": "A clean linear result and a literature value to compare with, which makes the conclusion easy. Use a series of cells to increase the signal to a few hundred mV."
  },
  {
   "id": "discharge-curves-for-capacitors-in-series-and-parallel",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Discharge curves for capacitors in series and parallel",
   "researchQuestion": "How does the number of identical 1000 μF capacitors in series (1 to 5) change the time constant when discharging through a 10 kΩ resistor?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Number of identical capacitors in series, 1 to 5; five values, with 3 to 5 discharge runs each.",
   "dependentVariable": "Voltage against time from a data logger or voltmeter with a stopwatch; time constant τ from the fitted exponential or from ln V against t.",
   "controlledVariables": "Same resistance value, measured with a multimeter; same initial voltage across the whole chain, for example 9 V; same capacitors, fully discharged first; same voltmeter input resistance.",
   "physicsNeeded": "Series: 1/C = Σ1/Cᵢ, and τ = RC. Plot ln V against t; the gradient is −1/τ. Then plot τ against 1/N, which should be a line through the origin with gradient RC.",
   "slVsHl": "SL: measure τ for each N and compare with the predicted values. Top band: include the voltmeter internal resistance and leakage current in the model. HL: RC in D.4 style analysis is not needed.",
   "whereMarksAreLost": "Research design: the question stated is voltage division and does not fit the data collected. Data analysis: reading a voltmeter by hand at fast decays. Evaluation: capacitor tolerances hide the trend.",
   "dataNote": "Needs capacitors, resistor and a logger; the main uncertainty is capacitor tolerance and the voltmeter loading the circuit.",
   "verdict": "Fine and easy, if you focus on time constant rather than vague voltage. Measure each capacitor first to keep the data honest."
  },
  {
   "id": "efficiency-of-a-small-dc-motor-lifting-a-load-2",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Efficiency of a small DC motor lifting a load",
   "researchQuestion": "How does the efficiency of a small DC motor change as the mass it lifts is increased from 20 g to 120 g in 20 g steps at a fixed supply voltage of 6.0 V?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Lifted mass from 20 g to 120 g, 6 values, each with 3 repeats.",
   "dependentVariable": "Electrical input power from a voltmeter and ammeter (P = VI), and useful output power from mgh over the time taken to lift by a fixed 0.80 m measured with a stopwatch or video. Efficiency is output divided by input.",
   "controlledVariables": "Supply voltage, checked on the voltmeter each run. Lift height, marked on a metre rule. Motor and string, using the same spool. Motor temperature, allowed to cool between runs.",
   "physicsNeeded": "Efficiency = mgh/(VIt). Plot efficiency against mass to find the peak. Alternatively plot output power against input power. The peak is expected at an intermediate load, as friction dominates at low load and stalling at high.",
   "slVsHl": "SL students plot efficiency against load and identify the maximum. Top band work explains it using the motor's resistive losses (I²R) and friction, and estimates the friction from a no load run. Input and output measurements need careful uncertainty handling.",
   "whereMarksAreLost": "Research design: a dynamometer is often unavailable, and a poor lifting setup makes speed inconsistent. Data analysis: current fluctuates as the motor runs, so a single reading is not enough. Conclusion: efficiency values above 100% or with no uncertainty. Evaluation: not addressing the starting transient and string stretch.",
   "dataNote": "Needs a small DC motor, a power supply, meters and a stopwatch. The main uncertainty is fluctuating current and the timing of a short lift.",
   "verdict": "A very workable version of the input without a dynamometer. It suits students who like practical circuits. Twist: repeat at three supply voltages and map where the best efficiency sits."
  },
  {
   "id": "filament-lamp-i-v-curve-at-different-starting-conditions",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Filament lamp I-V curve at different starting conditions",
   "researchQuestion": "How does the illumination of an LDR or the ambient temperature of a thermistor, varied over 5 conditions, change its current-voltage characteristic over 0 V to 5 V?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Thermistor bath temperature: 20, 30, 40, 50, 60 °C, 5 values (or LDR illumination measured with a light sensor at 5 distances). Voltage set in steps of 0.5 V from 0 V to 5 V at each.",
   "dependentVariable": "Current through the device from a multimeter (±0.001 A) and voltage across it from a second meter. Resistance R = V/I and the differential resistance dV/dI from the graph.",
   "controlledVariables": "Voltage range: kept low enough that self-heating is small, by using a short measurement time. Bath temperature: stirred, measured with a thermometer next to the device. Meters: same, connected in the same way. Waiting time: 1 minute at each temperature before reading.",
   "physicsNeeded": "For an NTC thermistor R = R₀ exp(B/T), so plot ln R against 1/T (in kelvin): gradient is B. Curves of I against V show that the device is non-ohmic due to self-heating at higher power. Compare the shift of the curve with temperature.",
   "slVsHl": "SL: plot I against V at each temperature and describe how the resistance changes. Top band or HL depth: linearise with ln R against 1/T, extract B and consider self-heating power V × I.",
   "whereMarksAreLost": "Research design: the input is vague, so choose one device and one variable and say why. Data analysis: only plotting curves without any quantity extracted. Conclusion: describing the shape with no numbers. Evaluation: ignoring self-heating of the device while measuring.",
   "dataNote": "A thermistor, a low-voltage supply, two meters and a water bath are enough; the main uncertainty is that the device is not at the same temperature as the bath.",
   "verdict": "Worth doing only if you commit to one device and get a number, such as the B value. Without that it stays a description and scores poorly."
  },
  {
   "id": "finding-emf-and-internal-resistance-of-a-aa-cell",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Finding emf and internal resistance of a AA cell",
   "researchQuestion": "What are the emf and internal resistance of an alkaline AA cell when the external resistance is varied from 2.2 ohm to 47 ohm?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "External resistance R, 7 to 8 values from 2.2 ohm to 47 ohm (or a decade box), each measured 3 times with the circuit closed only briefly.",
   "dependentVariable": "Terminal potential difference V from a digital voltmeter across the cell and current I from an ammeter in series. Emf and r come from the graph.",
   "controlledVariables": "Same cell throughout, with a fresh one for repeats. Circuit closed for about 2 s per reading to limit cell depletion and heating. Room temperature noted. Same meters and leads to keep contact resistance constant.",
   "physicsNeeded": "V = E - Ir. Plot V (y) against I (x): the intercept is E and the gradient is -r. Alternative: plot 1/I against R, where gradient is 1/E and intercept is r/E.",
   "slVsHl": "SL students get E and r with uncertainties from best and worst fit lines. Higher marks come from comparing with an open circuit voltage reading, checking whether r stays constant as the cell discharges, and comparing cell types or ages.",
   "whereMarksAreLost": "Research design: leaving the circuit on so the cell drains and the data drifts. Data analysis: not propagating uncertainty from both meters. Evaluation: ignoring meter resistance and contact resistance as sources of systematic error.",
   "dataNote": "Needs a cell holder, resistor set or decade box, two multimeters; main uncertainty is cell drift and the small voltage differences at high R.",
   "verdict": "Reliable, easy to do well, but very familiar to examiners. Make it your own by comparing cells of different age or type, or the same cell across a discharge, so the question is not just a textbook measurement."
  },
  {
   "id": "internal-resistance-of-a-4-5-v-battery-from-load-tests",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Internal resistance of a 4.5 V battery from load tests",
   "researchQuestion": "What is the internal resistance of a 4.5 V battery when the load resistance is varied from 5 Ω to 100 Ω in eight steps, and does it stay constant as current changes?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Load resistance from a decade box or set of resistors, 5, 10, 15, 22, 33, 47, 68 and 100 Ω, each measured twice.",
   "dependentVariable": "Terminal voltage with a digital voltmeter and current with an ammeter. Internal resistance found from the gradient of V against I.",
   "controlledVariables": "Battery: the same cell pack, with the circuit closed only briefly for each reading to limit drain. Temperature: resistors left to cool between readings. Meters: the same ones and ranges. Battery state: check the open circuit emf before and after the run.",
   "physicsNeeded": "V = ε − Ir. Plot V against I. The intercept is ε and the gradient magnitude is r. Also plot 1/I against R, where the gradient is 1/ε and the intercept is r/ε, as an independent check.",
   "slVsHl": "SL: one graph, values of ε and r with uncertainty. Top band: second linearisation for comparison, and a test of whether r changes with current or with battery drain. HL: no extra syllabus but a power transfer analysis adds depth.",
   "whereMarksAreLost": "Research design: battery drains during the run so emf drifts. Data analysis: not propagating uncertainty into the gradient. Evaluation: ignoring contact resistance and meter resistance.",
   "dataNote": "Basic circuit kit only; main uncertainty is the battery drifting, which the open circuit check exposes.",
   "verdict": "Very easy to get right and very common as a method. Add your own angle such as repeating on a used and a fresh battery to make the conclusion interesting."
  },
  {
   "id": "internal-resistance-of-a-cell-as-it-discharges",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Internal resistance of a cell as it discharges",
   "researchQuestion": "How does the internal resistance of an AA alkaline cell change as it is discharged, measured after each 10 minutes of a 10 Ω load over 60 minutes?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Discharge time through a fixed 10 Ω load: 0, 10, 20, 30, 40, 50, 60 minutes (7 values). At each stage, a full measurement using a variable resistor from 2 Ω to 47 Ω, 6 loads. Repeat with a second cell of the same batch.",
   "dependentVariable": "Terminal voltage V from a voltmeter (±0.01 V) and current I from an ammeter (±0.001 A), taking brief readings. Internal resistance r is the negative gradient of V against I, and EMF is the intercept.",
   "controlledVariables": "Cell temperature: check by touch or with a probe, and pause between readings so it does not warm up. Cell type and batch: the same brand, all bought at the same time. Reading time: under 5 seconds per load so the cell does not discharge. Contacts: same holder and clean leads.",
   "physicsNeeded": "ε = V + Ir so V = ε − Ir. Plot V against I: gradient is −r and y-intercept is ε. Then plot r against total discharge time or charge removed (in mAh) to see the trend.",
   "slVsHl": "SL: get r for each discharge stage, and plot r against time. Top band or HL depth: consider r changing with the current itself, use uncertainty in the gradient, and compare with a manufacturer datasheet.",
   "whereMarksAreLost": "Research design: the original idea covers two variables, so choose one. Data analysis: using only two loads to find r, so no evidence of linearity. Conclusion: not linking the rising r to the chemistry or to the fall in EMF. Evaluation: neglecting the resistance of the leads and meters.",
   "dataNote": "An AA cell, variable resistor and two meters are enough; the main uncertainty is contact resistance and the cell recovering between readings.",
   "verdict": "Standard but sound. Keeping to discharge state (not temperature) with a timed cycle makes it your own, and the trend in r is a clear result."
  },
  {
   "id": "internal-resistance-of-cells-from-a-load-current-sweep",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Internal resistance of cells from a load-current sweep",
   "researchQuestion": "What is the internal resistance r of a 1.5 V alkaline AA cell, from terminal voltage V against current I for load resistances from 1 Ω to 47 Ω in 8 steps, and how does r change as the cell is discharged over 60 minutes?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Load resistance R: 1, 2.2, 4.7, 10, 15, 22, 33, 47 Ω (8 values), each measured quickly to limit discharge. Repeat the sweep after set discharge intervals for the second part.",
   "dependentVariable": "Terminal voltage with a digital voltmeter and current with an ammeter (±0.01 A), 3 readings per load. Calculate r from the gradient of V against I.",
   "controlledVariables": "Cell brand and batch, using one new cell per run. Temperature, checked with a thermometer on the cell. Contact time, kept below 5 s per reading with a switch. Wire and contact resistance, kept low by short leads and clean clips.",
   "physicsNeeded": "V = ε − Ir. Plot V against I. The intercept is the EMF and the gradient is −r. Compare with the value from the short-circuit estimate.",
   "slVsHl": "SL students find r for one cell from the line with uncertainty. To reach the top, they study how r rises with discharge, or compare cell types, and account for lead resistance in the ammeter reading.",
   "whereMarksAreLost": "Research design: leaving the circuit on so the cell warms and depletes during the measurement. Data analysis: forcing the line through the origin or ignoring the meter resistance. Evaluation: not commenting on non-linearity at high current.",
   "dataNote": "Needs a cell, holder, resistor box or fixed resistors and two meters; the main uncertainty is drift from discharge and contact resistance.",
   "verdict": "Routine, but reliable if done well. The discharge-over-time part is the twist that lifts it above the standard version."
  },
  {
   "id": "led-brightness-against-forward-current-for-three-colours",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "LED brightness against forward current for three colours",
   "researchQuestion": "How does the illuminance measured 5.0 cm from a red, green and blue LED vary with forward current from 2 mA to 20 mA in steps of 2 mA?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Forward current set through the LED, 2 to 20 mA in 2 mA steps (10 values), for three LED colours, each setting repeated 3 times.",
   "dependentVariable": "Illuminance read with a lux meter or a light sensor connected to a data logger, at a fixed distance. Calculate mean and spread of the readings. Forward voltage read with a digital multimeter.",
   "controlledVariables": "Distance and alignment between LED and sensor fixed with a clamped tube or rail; room light removed by working in a dark box and subtracting a background reading; LED allowed to warm up for one minute before each reading; same LED package type for all colours.",
   "physicsNeeded": "LED is non-ohmic, so current rises exponentially with voltage, while light output is roughly proportional to current. Plot illuminance against current for each colour; the gradient gives relative efficiency. Also plot current against voltage to find the threshold voltage and link it to photon energy, using E = hc/λ.",
   "slVsHl": "SL: straight-line graphs for each colour, gradient comparison and uncertainty. Top band or HL depth: estimate Planck's constant from threshold voltages against 1/λ, and discuss the assumptions and heating effects.",
   "whereMarksAreLost": "Research design: using voltage as the IV without controlling the series resistor, so the current is uncontrolled. Data analysis: ignoring background light and sensor offset. Evaluation: not commenting on the sensor's spectral sensitivity varying with colour, which makes cross-colour comparison unfair.",
   "dataNote": "Needs a lux meter or light sensor plus a variable supply; the main uncertainty is sensor alignment and its colour-dependent response.",
   "verdict": "Worth choosing if you fix the current, not the voltage, and use the threshold voltages to get a Planck estimate, which makes it your own. Avoid comparing raw lux values between colours without a correction."
  },
  {
   "id": "layers-of-cellophane-and-solar-panel-power-output",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Layers of cellophane and solar panel power output",
   "researchQuestion": "How does the number of layers of clear cellophane (1 to 8 layers) covering a small solar panel affect its maximum power output under a fixed lamp?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Number of cellophane layers, 0 to 8 (9 values, each repeated 3 times); thickness is the layer count times the single-layer thickness, measured with a micrometer over a stack.",
   "dependentVariable": "Panel voltage and current across a load resistor, read with two multimeters, giving P = VI. Optionally use a lux or light sensor behind the film to get transmitted intensity, and efficiency as P divided by (intensity × panel area).",
   "controlledVariables": "Lamp distance and power fixed with a clamp and a ruler; ambient light blocked by a dark box or dark room; panel temperature kept constant by waiting between readings; load resistance fixed at the value that maximises power.",
   "physicsNeeded": "Beer-Lambert style attenuation I = I0 e^(−μx) for each layer. Plot ln(P) against number of layers; the gradient is −μ per layer, checking whether power follows the transmitted intensity. The efficiency question needs incident power, not only output.",
   "slVsHl": "An SL student can plot power against layers and describe the fall. Top band work linearises with a logarithm, extracts the attenuation coefficient, and separates reflection at each surface from absorption.",
   "whereMarksAreLost": "Research design: efficiency is claimed but incident power is never measured. Data analysis: exponential trend plotted as a straight line without justification. Evaluation: lamp heating the panel and film, and creases in the film.",
   "dataNote": "Needs a solar panel, lamp, two multimeters and cellophane; the main uncertainty is lamp output drifting as it warms, so warm it up first.",
   "verdict": "Cheap and reliable, and the log graph gives it real analysis depth. Use coloured film too, or measure the transmission with a light sensor, to make it your own."
  },
  {
   "id": "light-dependent-resistor-response-to-varying-illuminance",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Light dependent resistor response to varying illuminance",
   "researchQuestion": "How does the resistance of an LDR change as the illuminance from a lamp varies between 50 lux and 1000 lux, in about 8 steps?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Illuminance at the LDR, set by moving a lamp along a metre rule (about 8 to 10 distances) and checked with a lux meter; repeat each position 3 times.",
   "dependentVariable": "LDR resistance found from a multimeter in ohmmeter mode, or from voltage and current in a potential divider. Compute the mean resistance and its uncertainty.",
   "controlledVariables": "Same lamp and supply voltage, checked with a multimeter; LDR held at a fixed orientation in a clamp; room lights off and a black tube around the path; LDR temperature kept steady by short readings with a pause in between.",
   "physicsNeeded": "For many LDRs R follows a power law, R = kE^(-γ). Plot ln R against ln E; the gradient gives -γ. Illuminance from a point source follows an inverse square law, so a plot of 1/√E against distance can check the lamp behaves as a point source.",
   "slVsHl": "SL: log-log graph, exponent with uncertainty, and a comment on the fit. Top band: test the inverse square assumption for the lamp, and build a potential divider to show how the sensor output voltage varies.",
   "whereMarksAreLost": "Research design: relying on distance as a stand-in for intensity without a lux meter. Data analysis: applying a linear fit to a curved relationship. Evaluation: not addressing stray light and the slow recovery of an LDR after bright exposure.",
   "dataNote": "Needs an LDR, a multimeter and a lux meter or a calibrated app; the main uncertainty is the LDR's slow response and stray light.",
   "verdict": "A sound and cheap option, provided you state clearly that this is not the photoelectric effect. Measuring the exponent γ gives a clear result you can compare with the datasheet."
  },
  {
   "id": "pitch-angle-of-model-turbine-blades-and-power-delivered",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Pitch angle of model turbine blades and power delivered",
   "researchQuestion": "How does the blade pitch angle, varied from 0 to 60 degrees in 10 degree steps, affect the electrical power delivered by a model wind turbine to a 10 ohm load in a steady airflow?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Blade pitch angle, 7 values from 0 to 60 degrees, set with a protractor jig or printed template. Three runs per angle.",
   "dependentVariable": "Voltage across a fixed load resistor with a multimeter or logger; power P = V^2/R. Air speed at the turbine measured with an anemometer.",
   "controlledVariables": "Fan speed setting and distance from turbine to fan kept fixed, with air speed checked at the start of each run. Same blade set, number of blades and blade length. Same load resistor. Same start position and waiting time for the rotor to reach steady speed.",
   "physicsNeeded": "Power available in wind is P = 1/2 rho A v^3, with efficiency = P_electrical / P_wind. Plot efficiency or power (y) against pitch angle (x) to find the optimum. If air speed is varied instead, plot P against v^3, gradient linked to efficiency.",
   "slVsHl": "SL students find the optimum angle and give an efficiency. Higher marks come from checking the v^3 dependence, explaining why power drops at large angle (stall, less swept effect) and quantifying the air speed non-uniformity of a fan.",
   "whereMarksAreLost": "Research design: fan airflow is not uniform and not measured. Data analysis: reporting only voltage without converting to power or efficiency. Evaluation: blades made by hand differ from one another and were not checked.",
   "dataNote": "Needs a small DC motor turbine kit or 3D printed blades, a fan, anemometer and multimeter; main uncertainty is fan flow variation and blade construction.",
   "verdict": "Fun and relevant to energy topics, but easy to be sloppy. Worth choosing if you build your own blades and measure air speed properly; otherwise it stays descriptive."
  },
  {
   "id": "power-transfer-efficiency-against-load-resistance",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Power transfer efficiency against load resistance",
   "researchQuestion": "How does the load resistance, from 2 Ω to 100 Ω in eight values, affect the efficiency and the load power of a circuit powered by a 3 V battery pack with internal resistance?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Load resistance R, values of 2, 5, 10, 15, 22, 33, 68 and 100 Ω, from a decade box, two runs each.",
   "dependentVariable": "Terminal voltage and current with two multimeters. Load power = VI, efficiency = V/ε, where ε is the open circuit emf measured first.",
   "controlledVariables": "Battery: the same cells, checked for emf drift between runs. Time of connection: short, to limit heating and drain. Wires and contacts: same leads, tightened connections. Meters: ranges fixed.",
   "physicsNeeded": "Efficiency = R/(R + r) rises with R, while load power P = ε²R/(R + r)² peaks at R = r. Plot efficiency against R, and P against R, and find r from the peak. Linearise using 1/η = 1 + r/R against 1/R.",
   "slVsHl": "SL: measure and describe both curves, find r from a graph. Top band: compare r from three methods and explain why the maximum power point is only 50% efficient. HL: nothing extra.",
   "whereMarksAreLost": "Research design: efficiency never defined properly. Data analysis: no propagation into the peak position. Evaluation: overlooking battery drain and resistor heating.",
   "dataNote": "Simple circuit kit; small uncertainty in resistances, but battery drift needs the emf check.",
   "verdict": "Neat and cheap, with a memorable peak. The best twist is the comparison of the three ways to obtain internal resistance."
  },
  {
   "id": "rc-circuit-as-a-model-of-a-nerve-membrane",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "RC circuit as a model of a nerve membrane",
   "researchQuestion": "How does the time constant of a capacitor discharging through a resistor change as the resistance is varied from 10 kΩ to 100 kΩ in six steps, with a fixed 100 µF capacitor?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Resistance R: 10, 22, 33, 47, 68 and 100 kΩ (6 values), with 3 discharge runs for each.",
   "dependentVariable": "Voltage across the capacitor against time, recorded with a voltage sensor and data logger at 10 Hz or more. Time constant τ is found from the time for the voltage to fall to 37 % of its start value, or from the gradient of ln V against t.",
   "controlledVariables": "Same capacitor, checked with a meter and fully discharged between runs. Same starting voltage, for example 5.0 V from a fixed supply. Same wiring and meter or logger input resistance, because a multimeter of 10 MΩ affects the larger resistors. Room temperature steady.",
   "physicsNeeded": "Capacitor discharge V = V0 e^(−t/RC), so ln V = ln V0 − t/RC. Plot ln V against t, where the gradient is −1/RC. Then plot τ against R, where the gradient equals C. The link to nerves is an analogy: the membrane acts like a capacitor and ion channels like resistors, which sets how quickly a potential changes along a fibre.",
   "slVsHl": "SL students measure τ for each R and compare the gradient of τ against R with the labelled capacitance. Top band work checks the analogy critically, saying what the circuit model leaves out such as active ion pumping. HL students can extend to a cable model with several RC stages in series and look at how a pulse is delayed and smoothed.",
   "whereMarksAreLost": "Research design: as written, measuring current with a multimeter is too slow for a fast changing signal, so a logger is needed. Data analysis: capacitor tolerance is often 20 %, so use the measured C and not the label. Conclusion: overstating how well a circuit represents a real nerve. Evaluation: ignoring the internal resistance of the meter or logger and leakage in the capacitor.",
   "dataNote": "Needs a voltage sensor with logger, a 100 µF electrolytic capacitor and a resistor set. The main uncertainty is the capacitor tolerance and meter loading at high resistance.",
   "verdict": "Good physics with clean exponential data, worth choosing if you keep the biology as a short context. Make it personal by adding a second capacitor value or a chain of RC stages to model a longer fibre."
  },
  {
   "id": "resistance-and-heating-of-nichrome-wires-of-different-diameter",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Resistance and heating of nichrome wires of different diameter",
   "researchQuestion": "How does the diameter d of nichrome wire (d = 0.20 to 0.71 mm, six standard gauges, length 0.50 m) affect its resistance and the temperature rise in 60 s at a fixed 3.0 V supply?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Wire diameter measured with a micrometer at several points, six gauges from 0.20 to 0.71 mm, three separate pieces each where possible.",
   "dependentVariable": "Resistance R = V/I from a digital voltmeter and ammeter; temperature rise of the wire from a thermocouple or from the change in temperature of a fixed water volume around it. Power P = V²/R is calculated.",
   "controlledVariables": "Length: fixed at 0.50 m with a ruler between clamps. Material: the same nichrome reel. Potential difference: same stabilised supply, checked with the meter during the run. Start temperature and heating time: fixed with a thermometer and stopwatch. Current kept low so wire stays cool for the resistance part.",
   "physicsNeeded": "R = ρL/A = 4ρL/(π d²). Plot R against 1/d²; the gradient is 4ρL/π, so ρ can be found and compared with the nichrome data value of about 1.1 × 10⁻⁶ Ω m. Heating rate at fixed V is P = V²/R, so ΔT should also grow with d².",
   "slVsHl": "Fully SL. Top band work uses a propagated uncertainty where the diameter is squared, treats contact resistance and the change of resistance with temperature, and explains why the water heating gives lower power than V²/R.",
   "whereMarksAreLost": "Research design: heating and resistance mixed in one run so temperature changes the resistance being measured. Data analysis: uncertainty on d ignored, though d appears squared. Evaluation: heat loss to air and the clamps.",
   "dataNote": "Needs a power supply, micrometer, meters and a thermometer; the diameter uncertainty and heat loss to the surroundings dominate.",
   "verdict": "Good and clean if you keep resistance and heating as two separate measurements. The twist is to compare the ρ you obtain with a published value and explain the difference."
  },
  {
   "id": "resistance-by-ammeter-voltmeter-versus-ohmmeter-across-a-range",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Resistance by ammeter-voltmeter versus ohmmeter across a range",
   "researchQuestion": "How does the percentage difference between a resistance found from V and I readings and the same resistance read on a multimeter ohmmeter vary for resistors from 1 Ω to 1 MΩ (eight values)?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Nominal resistance of the resistor: 1 Ω, 10 Ω, 100 Ω, 1 kΩ, 10 kΩ, 100 kΩ, 470 kΩ, 1 MΩ (8 values), each measured five times.",
   "dependentVariable": "Percentage difference between R = V/I (digital voltmeter and ammeter on a 5 V supply) and the ohmmeter reading. Also compare each with the resistor's colour-code value.",
   "controlledVariables": "Supply voltage (fixed at 5.0 V); temperature of resistors (short measurement times to avoid heating); same meters and ranges recorded for each value; same leads and connections, with contact resistance checked by touching probes together.",
   "physicsNeeded": "R = V/I; a voltmeter of finite resistance in parallel with a large R lowers the reading, and an ammeter's resistance matters for small R. Plot percentage difference against log R and compare with the prediction from the meter's internal resistance.",
   "slVsHl": "SL can compare the two methods and explain the difference with meter resistance. To reach top band, model the difference quantitatively using the measured meter resistance and show the model matches the data.",
   "whereMarksAreLost": "Research design: RQ that is just 'compare two methods' with no quantity varied. Conclusion: stating one method is 'more accurate' without a reference value. Evaluation: ignoring lead resistance and the meter's range settings.",
   "dataNote": "Needs a power supply, two multimeters and a resistor set; the main uncertainty is meter resolution and lead resistance at the low end.",
   "verdict": "Simple, but it can become dull. Its value comes from explaining the pattern with meter resistance, so commit to that model early. Worth choosing if you like circuits."
  },
  {
   "id": "resistance-of-a-constantan-wire-against-its-length",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Resistance of a constantan wire against its length",
   "researchQuestion": "How does the length of a constantan wire, varied from 10.0 cm to 100.0 cm in 10.0 cm steps, affect its resistance, found from voltage and current readings at a fixed current of 0.20 A?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Length of constantan wire (0.100 m to 1.000 m, 10 values), measured between crocodile clips with a metre rule; three repeats at each length with the clips re-attached.",
   "dependentVariable": "Potential difference across the wire (digital multimeter, V) and current (ammeter, A); resistance R = V/I calculated for each length.",
   "controlledVariables": "Wire diameter: same reel throughout, checked with a micrometer at several points. Temperature: current kept low and switched on only briefly for each reading to limit heating. Supply: same fixed voltage source and same meters. Contact resistance: clips clean and clamped at the same pressure.",
   "physicsNeeded": "R = ρL/A, so R is proportional to L for a uniform wire. Plot R (y) against L (x): the gradient is ρ/A, so ρ = gradient × πd²/4. A non-zero intercept shows contact resistance. HL students can add the uncertainty in d, which dominates because A depends on d squared.",
   "slVsHl": "SL: straight-line graph, resistivity from gradient and comparison with a data-book value. Top band: a treatment of the intercept, error bars from repeats, a maximum and minimum gradient, and a test of the heating effect by repeating at two currents. The physics is the same at HL, so the depth comes from the analysis.",
   "whereMarksAreLost": "Research design: leaving the wire heating up, or not saying why current is kept small. Data analysis: ignoring the diameter uncertainty and using a single diameter reading. Conclusion: giving ρ without comparing it to an accepted value and a percentage difference. Evaluation: not naming contact resistance and the clip position error as systematic effects.",
   "dataNote": "Needs a constantan or nichrome wire, a power supply, two meters and a micrometer; the main uncertainty is the diameter and the clip contact.",
   "verdict": "Sound and easy to get clean data from, but very common in schools, so it needs a twist: compare two metals, or test temperature dependence with a water bath. Pick it if you want a safe, high-quality analysis rather than novelty."
  },
  {
   "id": "resistance-of-copper-coil-and-peltier-against-temperature",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Resistance of copper coil and Peltier against temperature",
   "researchQuestion": "How does temperature, from 30 °C to 80 °C in 10 °C steps, affect the resistance of a coil of copper wire and of a Peltier module, and how do their temperature coefficients differ?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Temperature of a water bath: 30, 40, 50, 60, 70 and 80 °C, with two readings on heating and two on cooling.",
   "dependentVariable": "Resistance found from a four wire or a low current voltmeter and ammeter measurement, or a digital ohmmeter. Bath temperature with a digital thermometer placed next to the sample.",
   "controlledVariables": "Current: kept small, under 0.1 A, to avoid self heating. Samples: sealed against water with waterproof coating, same sample each time. Thermal equilibrium: wait 2 minutes after each set point with stirring. Lead resistance: subtracted or removed with the four wire method.",
   "physicsNeeded": "For a metal, R = R₀(1 + αΔT), so plot R against T with gradient R₀α. Semiconductor resistance depends on carrier density, and the Peltier is expected to show a different trend, possibly a smaller or opposite coefficient. Compare α of copper with its literature value of about 0.004 per K.",
   "slVsHl": "SL: plot R against T for both and compare gradients. Top band: fit models, compute α with uncertainty and explain trend by charge carriers and lattice vibration. HL: none specific.",
   "whereMarksAreLost": "Research design: not sealing samples, or temperature lag between bath and sample. Data analysis: no fit uncertainty. Evaluation: heating and cooling hysteresis ignored.",
   "dataNote": "Needs a hot water bath, a sealed sample and a precise meter; copper resistance changes are small, so lead resistance matters.",
   "verdict": "Interesting because of the contrast between the two materials. Keep it manageable by choosing four wire measurement and being clear on why the Peltier behaves differently."
  },
  {
   "id": "resistance-of-pencil-leads-with-different-hardness-grades",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Resistance of pencil leads with different hardness grades",
   "researchQuestion": "How does the hardness grade of a pencil lead (from 6B to 6H, 8 grades) affect its resistivity, in Ω m, when 5.0 cm lengths are used in a low voltage circuit?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Pencil grade, 8 values such as 6B, 4B, 2B, HB, F, 2H, 4H, 6H, with 3 different leads of each grade. Graphite fraction is not printed on the pencil, so grade is the honest variable.",
   "dependentVariable": "Resistance from a voltmeter and ammeter (or a four-wire ohmmeter), giving R = V/I. Diameter is measured with a micrometer at 5 places and length with a ruler, then resistivity ρ = RA/L is calculated.",
   "controlledVariables": "Length between contacts: fixed with clips at a marked separation. Current: kept low (below 0.1 A) to limit heating. Lead diameter: measured and included in the area calculation. Temperature: readings taken quickly with the current off between readings.",
   "physicsNeeded": "R = ρL/A. For one grade, plot R against L to find ρ from the gradient times A. Then compare ρ across grades. Composition can be discussed only qualitatively, since graphite to clay ratio is not printed.",
   "slVsHl": "SL: measure R and ρ for each grade and describe the trend. Deeper: measure R for several lengths of each grade so that ρ comes from a gradient, and assess contact resistance using the intercept.",
   "whereMarksAreLost": "Research design: using the graphite percentage as the variable when it is unknown, and using mechanical pencil leads with the wrong diameter. Data analysis: ignoring how varied the diameter is along a lead. Conclusion: claiming a link with graphite content that was not measured. Evaluation: contact resistance and heating not addressed.",
   "dataNote": "Needs a micrometer and a low resistance measurement setup; contact resistance at crocodile clips is the main uncertainty.",
   "verdict": "Worth choosing only if you rewrite the variable as grade and use lengths for a gradient. A twist is to test drawn graphite lines on paper as well, but the thin film makes it harder."
  },
  {
   "id": "resistance-of-saltwater-against-salt-mass",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Resistance of saltwater against salt mass",
   "researchQuestion": "How does the mass of table salt dissolved in 200 cm³ of water, from 0.5 g to 3.0 g in steps of 0.5 g, affect the resistance between two parallel electrodes 3.0 cm apart?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Mass of salt in 200 cm³ of water: 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 g, with three readings per solution.",
   "dependentVariable": "Resistance from an alternating supply of about 1 kHz, or a low voltage AC supply, using a voltmeter and ammeter. R = V/I. Use AC to avoid electrolysis and polarisation at the electrodes.",
   "controlledVariables": "Electrode spacing and immersed area: fixed by a clamp and a marked depth. Solution temperature: measured and kept near 20 °C. Solution volume: the same each time. Stirring: same time and no bubbles on the electrodes.",
   "physicsNeeded": "R = ρL/A, and conductivity rises with ion concentration, so R should fall roughly as 1/c at low concentration. Plot 1/R against concentration and expect a straight line whose gradient gives a geometric factor times the molar conductivity.",
   "slVsHl": "SL: measure, plot 1/R against concentration and comment on trend. Top band: derive conductivity, compare with a literature value and explain deviation at higher concentration. HL: none specific.",
   "whereMarksAreLost": "Research design: using DC, which polarises the electrodes and gives drifting readings. Data analysis: plotting R against mass and not linearising. Evaluation: temperature change from the current heating the solution.",
   "dataNote": "A beaker, electrodes, a low voltage AC supply or signal generator and two meters; polarisation with DC is the main trap.",
   "verdict": "Good and cheap if you use AC and think about geometry. Choosing a range that reaches the linear region and back it with conductivity data."
  },
  {
   "id": "resistivity-of-a-wire-from-its-v-i-gradient",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Resistivity of a wire from its V-I gradient",
   "researchQuestion": "What is the resistivity of nichrome wire, found from the gradient of a potential difference against current graph, for wire lengths from 0.20 m to 1.00 m in steps of 0.20 m?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Length of wire between crocodile clips: 5 to 6 values from 0.20 to 1.00 m; for each length, the current is varied with a rheostat over about 8 settings.",
   "dependentVariable": "Potential difference across the wire measured with a digital voltmeter, and current with an ammeter; resistance from each V-I gradient, then resistivity from resistance, cross-sectional area and length. Diameter measured with a micrometer at several points.",
   "controlledVariables": "Temperature: currents kept below about 0.5 A with short switch-on times so heating is small. Wire material and diameter: one reel used throughout. Contact resistance: clips placed at the same firm positions, and a four-wire style connection where possible. Wire straight and not coiled.",
   "physicsNeeded": "R = rho L / A and V = IR. Plot V against I for each length to get R, then plot R against L; the gradient equals rho / A, so rho = gradient times A.",
   "slVsHl": "SL students get R from the gradient and then rho. Higher depth comes from propagating the diameter uncertainty (which enters squared), checking for heating curvature in the V-I line, and comparing with a data book value.",
   "whereMarksAreLost": "Research design: leaving the current on so the wire heats, ignoring diameter measurement at several points. Data analysis: uncertainty in area not propagated. Evaluation: not discussing contact resistance and the nonzero intercept of R against L.",
   "dataNote": "Power supply, rheostat, two meters, metre rule and micrometer; the main uncertainty is the wire diameter and contact resistance.",
   "verdict": "A solid, safe choice, but the plain Ohm version is thin. Two nested graphs (V-I, then R-L) and a real heating check make it worth doing."
  },
  {
   "id": "resistivity-of-metals-compared-by-wire-length-method",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Resistivity of metals compared by wire length method",
   "researchQuestion": "How does the resistivity of copper, constantan, nichrome and iron wires of equal diameter compare, found from resistance measured at lengths from 0.20 m to 1.00 m?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Wire length, five values from 0.20 m to 1.00 m for each of the four materials, with material as a second comparison.",
   "dependentVariable": "Potential difference and current for each length, measured with a digital voltmeter and ammeter, three repeats. Resistance is V/I. Resistivity from the gradient of R against L and the cross-section from a micrometer diameter.",
   "controlledVariables": "Diameter, measured at three points with a micrometer. Current kept below 0.3 A and readings taken quickly to avoid heating. Temperature recorded. Contact points made by crocodile clips at the same pressure, or a four-wire method.",
   "physicsNeeded": "R = ρL/A. Plot R against L; the gradient is ρ/A, so ρ = gradient × A. The conductivity is σ = 1/ρ.",
   "slVsHl": "SL students calculate ρ for each metal and compare with data book values. Higher marks come from a percentage difference analysis, contact resistance from the intercept, and temperature effects.",
   "whereMarksAreLost": "Research design: material type alone gives only one point per metal, so length must be varied. Data analysis: uncertainty in the diameter, which is squared. Evaluation: heating and contact resistance.",
   "dataNote": "Wire reels, micrometer and meters from a school kit; the diameter uncertainty is the largest contribution to error in ρ.",
   "verdict": "Sound and manageable. Very common with a single wire, so the comparison across four metals and an intercept discussion make it worth choosing."
  },
  {
   "id": "solar-cell-output-against-lamp-distance",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Solar cell output against lamp distance",
   "researchQuestion": "How does the distance d between a lamp and a small solar cell, varied from 10 cm to 60 cm, affect the short circuit current and the power delivered to a fixed load?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Distance from lamp to cell: 10, 15, 20, 30, 40, 50, 60 cm (7 values), 3 repeats each, measured along a metre rule.",
   "dependentVariable": "Short circuit current and open circuit voltage with multimeters, and the power P = V²/R across a fixed load resistor. Light intensity is measured directly with a lux meter or phone sensor as a check.",
   "controlledVariables": "Same lamp, warmed up for 5 minutes before readings. Cell face perpendicular to the lamp axis using a fixed holder. Room darkened and covered to reduce stray light. Cell temperature kept steady by pausing between runs.",
   "physicsNeeded": "Intensity I ∝ 1/d² for a point source. Short circuit current is roughly proportional to I, so plot current against 1/d². Voltage rises only logarithmically with intensity, so open circuit voltage against ln(I) is a good second graph.",
   "slVsHl": "SL: current against 1/d² and comment on the linearity. Top band: separate the two behaviours of current and voltage, and explain why a lamp of finite size fails the point source model at short distance. HL depth: explain the logarithmic voltage dependence using the diode equation.",
   "whereMarksAreLost": "Research design: choosing voltage as the dependent variable, which does not follow the inverse square law and confuses the analysis. Data analysis: not measuring d from the filament position. Conclusion: assuming a point source at 10 cm. Evaluation: ignoring reflections and cell heating.",
   "dataNote": "Needs a lamp, a small solar cell, two multimeters and a rule; the main uncertainty is the true source position and stray light.",
   "verdict": "Worth doing, but only with current or power as the main variable, not voltage alone. Twist: compare an LED and a filament lamp, and see which one fits 1/d² better."
  },
  {
   "id": "testing-ohm-s-law-for-a-resistor-and-a-filament-lamp",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Testing Ohm's law for a resistor and a filament lamp",
   "researchQuestion": "How does the current through a fixed resistor and through a 6 V filament lamp change as the potential difference is raised from 0.5 V to 6.0 V in steps of 0.5 V, and over what range is each component ohmic?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Potential difference across the component from 0.5 V to 6.0 V using a variable power supply or potentiometer: at least 8 values, each measured 3 times, in both rising and falling order.",
   "dependentVariable": "Current in amperes read from an ammeter or data logger; resistance calculated as V divided by I at each point, and gradient of the I-V graph.",
   "controlledVariables": "Component temperature: the resistor is left to cool between readings and readings are taken quickly. Room temperature: recorded at the start and end. Meter ranges: kept fixed to avoid changing internal resistance. Same leads and connections.",
   "physicsNeeded": "V = IR for an ohmic conductor gives a straight line through the origin. The lamp filament heats and its resistance rises, so the I-V curve bends. Plot I against V and also R against V, or R against power dissipated.",
   "slVsHl": "SL students plot both components and state where linearity fails. To reach a higher standard, link the lamp resistance to filament temperature using a resistivity-temperature model and estimate the filament temperature.",
   "whereMarksAreLost": "Research design: only testing an ideal resistor, so nothing is really investigated. Data analysis: not using error bars from meter resolution. Conclusion: claiming Ohm's law is proved instead of saying it holds within uncertainty over a stated range.",
   "dataNote": "Only a power supply, two multimeters, a resistor and a lamp are needed; the main uncertainty is meter resolution and self-heating.",
   "verdict": "Only worth doing with the lamp or another non-ohmic part included, otherwise it is too basic. Estimating filament temperature makes it your own."
  },
  {
   "id": "testing-ohm-s-law-on-a-resistor-and-a-filament-lamp",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Testing Ohm's law on a resistor and a filament lamp",
   "researchQuestion": "How does the potential difference across a 100 ohm resistor and a 12 V filament lamp, varied from 0.5 V to 6.0 V in 0.5 V steps, affect the current, and does the resistance stay constant?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Potential difference from 0.5 V to 6.0 V, 12 values, set with a variable power supply or a potentiometer arrangement.",
   "dependentVariable": "Current read from a digital ammeter, three repeats per voltage, with voltage read on a voltmeter across the component. Resistance calculated as V/I at each point.",
   "controlledVariables": "Temperature of the resistor, kept low by short readings and switching off between values. Same meter ranges throughout. Same leads and connections to avoid contact resistance changes. Room temperature recorded.",
   "physicsNeeded": "V = IR. Plot I against V; the gradient is 1/R for the resistor. For the lamp the curve shows resistance rising with temperature, so also plot R against V or power.",
   "slVsHl": "SL students confirm linearity for the resistor and describe the lamp curve. Higher marks come from quantifying the deviation, estimating filament temperature from resistance, and comparing meter uncertainties with the scatter.",
   "whereMarksAreLost": "Research design: a fixed resistor alone gives a trivial answer with no real question. Conclusion: claiming Ohm's law 'proved' without a quantitative test. Evaluation: ignoring heating and meter internal resistance.",
   "dataNote": "Standard school kit; main uncertainty is resistor heating and the meter's last-digit resolution.",
   "verdict": "Very common and low in depth if you use only a fixed resistor. Worth it only with the lamp or a thermistor comparison, which gives you something to explain."
  },
  {
   "id": "time-constant-of-a-discharging-capacitor-across-five-capacitances",
   "topic": "B.5",
   "topicName": "Current and circuits",
   "level": "both",
   "title": "Time constant of a discharging capacitor across five capacitances",
   "researchQuestion": "How does the time constant of a capacitor discharging through a fixed 100 kilohm resistor change as capacitance is varied from 100 microfarad to 1000 microfarad?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Capacitance C, 5 to 6 values from 100 to 1000 microfarad (using single capacitors or parallel combinations), each discharge repeated 3 times.",
   "dependentVariable": "Voltage across the capacitor recorded against time with a data logger or a multimeter filmed on video every 5 s. The time constant is found from the slope of ln V against t, or the time to fall to V0/e.",
   "controlledVariables": "Same resistor, with its actual value checked by a multimeter. Same starting voltage, for example 6.0 V. Capacitor fully discharged and charged for the same time before each run. Same meter, since its input resistance acts in parallel with the circuit.",
   "physicsNeeded": "V = V0 exp(-t/RC). Plot ln V (y) against t (x): gradient is -1/RC. Then plot the time constant against C: the gradient should be R.",
   "slVsHl": "SL students can do the tau against C graph and compare gradient with the resistor value. Stronger work explains why the multimeter's own resistance reduces tau and handles capacitor tolerance (often 20 percent) by measuring C directly. HL students can link to exponential decay and energy stored.",
   "whereMarksAreLost": "Data analysis: using nominal capacitor values despite wide tolerances. Evaluation: not noticing meter resistance or leakage current. Conclusion: claiming agreement without comparing to a percentage difference and uncertainty.",
   "dataNote": "Needs electrolytic capacitors, resistor, power supply and a logger or video timing; main uncertainty is capacitor tolerance and meter loading.",
   "verdict": "Good, clean physics with an obvious linear graph. Choose it if you can get a logger; note that it is a standard investigation so the depth of your error handling has to set you apart."
  },
  {
   "id": "testing-t-squared-against-length-for-a-simple-pendulum",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Testing T squared against length for a simple pendulum",
   "researchQuestion": "How does the length L of a simple pendulum, varied from 0.20 m to 1.00 m in steps of 0.10 m, affect its period T, and does the gradient of T² against L match 4π²/g?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 3,
   "independentVariable": "String length from pivot to centre of the bob, 0.20 to 1.00 m, 9 values, each set up three times.",
   "dependentVariable": "Time for 20 oscillations with a stopwatch or a light gate, divided by 20 to give T. Then T² is calculated and g is found from the gradient.",
   "controlledVariables": "Release angle kept under 10° using a printed protractor sheet clamped behind the string. Same steel bob throughout. Same thin inextensible thread. Pivot held in a clamp with a slit so the length does not creep.",
   "physicsNeeded": "T = 2π√(L/g) for small angles. Plot T² (y) against L (x). The gradient is 4π²/g, so g = 4π²/gradient. A non-zero intercept points to a length measurement error, for example the bob radius.",
   "slVsHl": "SL students can plot the line, extract g and compare with 9.81 m/s². To reach the top band, add a proper uncertainty analysis with max and min gradients and explain any intercept. HL students can go further by fitting a power law T = kLⁿ and testing whether n = 0.5 within uncertainty.",
   "whereMarksAreLost": "Research design: no justification for the range of L or for keeping the angle small. Data analysis: uncertainty in T taken from the stopwatch resolution rather than from spread and reaction time. Conclusion: g quoted without a percentage difference from the accepted value. Evaluation: this topic is heavily used, so weak, generic evaluation stands out.",
   "dataNote": "Needs only a stand, thread, bob, metre rule and stopwatch, and the main uncertainty is timing reaction time and measuring L to the bob centre.",
   "verdict": "Very safe but also very common, so it will not impress by itself. Make it yours by measuring g for a specific reason, such as comparing it with a phone accelerometer value or checking it at your own location, and be strict about the intercept."
  },
  {
   "id": "where-the-small-angle-pendulum-formula-stops-working",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Where the small-angle pendulum formula stops working",
   "researchQuestion": "How does the measured period of a 1.00 m pendulum change as the release angle increases from 5° to 80° in steps of 15° or so, and at what angle does it differ from 2π√(L/g) by more than the uncertainty?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 3,
   "independentVariable": "Release angle, 5°, 10°, 20°, 30°, 45°, 60°, 70°, 80°, each with three repeats.",
   "dependentVariable": "Period from video analysis at 240 fps or a light gate over 10 swings. Calculated quantity is the percentage difference between the measured T and the small-angle T₀.",
   "controlledVariables": "Length fixed and measured once with a rule and again after the experiment. Same bob and thread. Room draughts limited by working away from doors. Number of swings timed kept identical so amplitude decay is similar.",
   "physicsNeeded": "T₀ = 2π√(L/g), while the exact period is T ≈ T₀(1 + θ₀²/16 + 11θ₀⁴/3072 + …) with θ₀ in radians. Plot T/T₀ (y) against θ₀² (x). The gradient should be near 1/16 for modest angles.",
   "slVsHl": "SL students can plot T against angle and state where the deviation exceeds error bars. Top band work compares against the series correction and discusses damping. HL students can compare with the elliptic integral result numerically.",
   "whereMarksAreLost": "Research design: angle measured by eye, giving large uncertainty on small angles. Data analysis: uncertainty in θ ignored when deciding where deviation starts. Conclusion: claiming a single failure angle without a stated threshold. Evaluation: amplitude decay during timing not discussed.",
   "dataNote": "A phone camera in slow motion or a light gate is needed, and the biggest uncertainty is reading the release angle and amplitude loss over several swings.",
   "verdict": "Much better than the plain length and period task because it asks where a model breaks, which is what examiners like. Choose it if you are comfortable with a little series expansion."
  },
  {
   "id": "effective-spring-mass-from-oscillation-period-against-load",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Effective spring mass from oscillation period against load",
   "researchQuestion": "How does the period of a vertical spring oscillator depend on the hanging mass from 50 g to 300 g, and what fraction of the spring's own mass is effective?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Hanging mass from 50 g to 300 g in 50 g steps, six values, with the period timed over 20 oscillations and repeated three times.",
   "dependentVariable": "Period found by timing 20 oscillations with a stopwatch or by a motion sensor or a phone video. Calculate T² and compare with the load.",
   "controlledVariables": "Same spring, with the amplitude fixed at about 2 cm and checked by a ruler. Same starting point and release without sideways motion. Same clamp height. Masses measured on a balance and the spring mass measured separately.",
   "physicsNeeded": "T² = 4π²(m + ms/3)/k for a spring of mass ms. Plot T² against m. The gradient is 4π²/k and the negative intercept on the m axis is ms/3, which can be checked against the balance.",
   "slVsHl": "SL can find k and show T² is linear in m. Top marks come from getting the intercept and testing the one third factor against the measured spring mass, and checking k against a static extension test. HL can derive the one third factor by integrating the kinetic energy of the spring.",
   "whereMarksAreLost": "Data analysis: plotting T against m and not linearising, or forcing the line through the origin. Evaluation: timing errors on few oscillations and ignoring damping and non-linear extension at low load. Research design: no independent check of k.",
   "dataNote": "Needs a spring, slotted masses, clamp stand, stopwatch or phone; the main uncertainty is reaction time, reduced by timing many swings.",
   "verdict": "Basic but very safe, and the intercept analysis lifts it above the ordinary version. Twist: compare two springs of different mass to see the ms/3 term change."
  },
  {
   "id": "card-area-and-amplitude-decay-of-a-spring-mass-oscillator",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Card area and amplitude decay of a spring mass oscillator",
   "researchQuestion": "How does the area of a card (10 to 100 cm^2, 6 values) fixed to a mass on a spring affect the amplitude remaining after 20 oscillations?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Card area from 10 to 100 cm^2, cut from the same card into 6 sizes and measured with a ruler. Three trials per size.",
   "dependentVariable": "Amplitude after 20 oscillations from a phone slow video against a ruler, or a motion sensor; calculate the ratio A20/A0 and the damping constant from ln(A20/A0).",
   "controlledVariables": "Starting amplitude fixed at 5.0 cm; total oscillating mass kept constant by adding plasticine to smaller cards; same spring; card kept horizontal and flat facing the motion.",
   "physicsNeeded": "Air drag is roughly proportional to area and v squared, giving amplitude decay. For light damping A = A0 exp(-bt/2m); plot ln(A20/A0) against area and test proportionality.",
   "slVsHl": "SL students plot ratio against area and describe the trend. Top band work justifies whether drag is linear or quadratic, and compares damping constants using ln of amplitude.",
   "whereMarksAreLost": "Research design: the card mass changes with area and hides the effect. Data analysis: reading amplitude off a video with large parallax. Evaluation: the spring's own damping and card tilt are not discussed.",
   "dataNote": "Needs a spring, masses and phone video; the main uncertainty is amplitude reading, so use a ruler in the frame and a tripod.",
   "verdict": "Solid and doable. Equalising the mass across cards is the detail that makes it credible, and adding a bare-mass run gives a proper baseline."
  },
  {
   "id": "damping-of-a-pendulum-swinging-in-liquids-of-different-viscosity",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Damping of a pendulum swinging in liquids of different viscosity",
   "researchQuestion": "How does the amplitude decay constant of a pendulum bob in water change as glycerol is added, from 0% to 50% by volume in 10% steps?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Glycerol concentration in the water, 0 to 50% by volume in 6 values, prepared in a tall container; 3 runs at each concentration.",
   "dependentVariable": "Amplitude read from a video at 60 fps or more, using Tracker software, at successive peaks. Calculate the decay constant from the gradient of ln(amplitude) against time. Also record the period.",
   "controlledVariables": "Same bob, string and pivot point; same starting amplitude of about 5 degrees; liquid temperature checked with a thermometer, as viscosity is temperature dependent; bob fully submerged at the same depth with the container wide enough to avoid wall effects.",
   "physicsNeeded": "Damped oscillation has amplitude A = A0 e^(-γt). Plot ln A against t; the gradient is -γ. For small speeds the drag is proportional to velocity, so γ should rise linearly with viscosity; plot γ against viscosity from tables.",
   "slVsHl": "SL: decay constants and a graph of γ against concentration. Top band or HL: compare with the Stokes' drag prediction, discuss the Reynolds number, and account for the added mass of displaced liquid, which changes the period.",
   "whereMarksAreLost": "Research design: using different fluids with no way to measure or quote viscosity. Data analysis: reading the amplitude by eye instead of from video. Evaluation: ignoring that the drag becomes quadratic at higher speed and that the temperature drifts.",
   "dataNote": "Needs a video camera or phone, Tracker and glycerol; the main uncertainty is reading the amplitude and the viscosity values from tables.",
   "verdict": "Much better than a simple fluid comparison, because the glycerol mixture gives a numerical IV. Use a small dense bob and a slow swing so the drag stays roughly linear."
  },
  {
   "id": "damping-strength-and-decay-constant-of-a-mass-on-a-spring",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Damping strength and decay constant of a mass on a spring",
   "researchQuestion": "How does the area of a card vane (0 to 100 cm², six values) attached to an oscillating mass-spring system affect the decay constant of its amplitude?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Vane area attached beneath a 200 g mass on a spring: 0, 20, 40, 60, 80, 100 cm² (six values), three runs each.",
   "dependentVariable": "Peak amplitude for successive oscillations, taken from video analysis (Tracker) or a motion sensor. Decay constant λ found from the gradient of ln(A) against time.",
   "controlledVariables": "Mass and spring (same ones throughout); initial amplitude (release from the same 5 cm displacement using a marked stop); vane shape and card thickness (same card, cut to size); air conditions (no draughts, doors shut).",
   "physicsNeeded": "Light damping gives A = A₀e^(−λt). Plot ln A against t, so the gradient is −λ. Then plot λ against vane area and test for proportionality, reasoning that drag rises with area.",
   "slVsHl": "SL students can extract λ and describe the trend. HL depth: relate λ to b/2m for a damping force −bv, and examine whether b is linear in area or follows a v² drag law at larger amplitudes.",
   "whereMarksAreLost": "Data analysis: reading peaks by eye from video frames, giving noisy ln A; not checking the graph is linear. Research design: amplitude too small to measure past a few cycles. Evaluation: ignoring that drag may not be linear in speed.",
   "dataNote": "Spring, masses, card and a phone camera with Tracker; the main uncertainty is peak position from video frame rate and mass wobble.",
   "verdict": "A good, feasible choice with plenty of room for analysis. Keep the damping light so you get enough cycles, and test whether the decay is truly exponential."
  },
  {
   "id": "does-bob-mass-change-pendulum-period-a-precision-test",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Does bob mass change pendulum period? A precision test",
   "researchQuestion": "Does the period of a simple pendulum of length 0.80 m released from 10 degrees change when the bob mass is varied from 20 g to 200 g in six steps?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Bob mass: 20, 50, 80, 110, 150, 200 g brass or steel slotted masses, with five repeats of each.",
   "dependentVariable": "Time for 20 oscillations with a light gate or phone video at 60 fps, giving period T = t/20 with uncertainty from the spread of repeats.",
   "controlledVariables": "Length measured from pivot to centre of mass of the bob, checked after each mass change. Release angle marked on a protractor board at 10 degrees. Same thread and pivot clamp. Bob size kept similar so drag does not change.",
   "physicsNeeded": "T = 2π√(L/g), independent of mass for small angles. Plot T against mass and fit a line: a gradient consistent with zero within uncertainty supports the theory. Better, compare T² against L for several lengths to get g as a second check.",
   "slVsHl": "SL: show the null result with proper error bars. Top band: quantify how small a mass effect could be detected, and study where mass does matter, such as air drag with a light, large bob, or a heavy thread whose mass adds to the effective moment of inertia.",
   "whereMarksAreLost": "Research design: expecting a dramatic trend, using bobs that also change in size, and timing one swing only. Data analysis: no uncertainty in the gradient. Conclusion: saying 'no effect' without stating the range that is consistent with zero. Evaluation: ignoring the length shift when masses are swapped.",
   "dataNote": "Stopwatch, clamp stand and masses are enough, but a light gate greatly reduces reaction-time uncertainty.",
   "verdict": "A very common topic and the answer is known in advance, so it scores only if you handle the null result carefully. Add a twist such as a hanging thread of measurable mass or a hollow versus solid bob."
  },
  {
   "id": "does-g-from-a-pendulum-depend-on-string-length",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Does g from a pendulum depend on string length?",
   "researchQuestion": "How does the value of g, calculated from the period of a simple pendulum, change as the string length is varied from 0.30 m to 1.20 m in steps of 0.15 m?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Length of the pendulum, measured from the suspension point to the middle of the bob, at 7 values from 0.30 m to 1.20 m in 0.15 m steps. Each length is set up three times, with the string re-clamped each time.",
   "dependentVariable": "Time for 20 complete oscillations measured with a stopwatch or a light gate with timer, repeated 3 to 5 times per length. The period T is the time divided by 20, and g is calculated from g = 4π²L/T².",
   "controlledVariables": "Release angle kept under 10° by marking a fixed displacement on a protractor or a paper scale behind the bob. Bob mass and size kept identical by using one dense metal sphere. String type kept the same, thin and inextensible, clamped firmly at a fixed point. Same timing method and starting point (the centre of the swing, using a fiducial marker) for every run.",
   "physicsNeeded": "For small angles T = 2π√(L/g). Plot T² against L: a straight line through the origin with gradient 4π²/g gives g from the fit. Also plot the individual g values against L to check whether any trend shows a systematic error, and compare the fitted g with 9.81 m s⁻² using the uncertainty from the gradient (maximum and minimum lines).",
   "slVsHl": "An SL student can collect the data, plot T² against L and compare the gradient-based g with the accepted value with propagated uncertainties. To reach the top band, add a quantified systematic effect, such as the bob's finite size (physical pendulum correction), the amplitude correction to the period, or the effect of the clamp, and show whether the g against L trend disappears once corrected. HL depth could use the moment of inertia of the bob to derive the physical pendulum period.",
   "whereMarksAreLost": "Research design: the RQ asks about variation of g with L, but g is a constant, so a weak design just expects a flat line without explaining why it might not be flat. Data analysis: timing only a few swings, ignoring the reaction time uncertainty, or averaging g values without a graph. Conclusion: stating that g equals 9.81 without a percentage difference tested against the uncertainty. Evaluation: not identifying the systematic errors (length measured to the wrong point, amplitude too large, string stretch), and giving vague fixes such as 'use a better stopwatch'.",
   "dataNote": "Needs a retort stand, string, metal bob, metre rule and stopwatch (or light gate); the main uncertainty is the length measured to the bob's centre of mass and human reaction time in timing.",
   "verdict": "A very common and accessible experiment, so it only earns high marks if you treat it as a test of whether g really is constant and analyse systematic errors carefully. Make it personal by using a location such as a stairwell for long lengths, or by comparing timing with a phone video frame count against a light gate."
  },
  {
   "id": "does-sphere-size-change-rolling-oscillation-on-a-curved-track",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Does sphere size change rolling oscillation on a curved track",
   "researchQuestion": "How does the radius of a solid sphere (0.5 to 2.0 cm, 6 sizes) affect its oscillation period when rolling in a curved track of radius 50 cm?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Sphere radius from 0.5 to 2.0 cm, using ball bearings or marbles, measured with vernier callipers. Five period measurements per ball.",
   "dependentVariable": "Time for 10 oscillations from phone video or a light gate, divided by 10 to get T. Compare with the predicted T using effective radius R - r.",
   "controlledVariables": "Same track and surface; small release angle under 10 degrees; same material (steel) where possible; track levelled with a spirit level.",
   "physicsNeeded": "A solid sphere rolling without slipping in a bowl of radius R has T = 2 pi sqrt(7(R - r)/(5g)). Plot T^2 against (R - r); the gradient is 28 pi^2/(5g). Test whether T is independent of mass.",
   "slVsHl": "SL students compare T against r and check the trend. Top band work derives the 7/5 factor from rotational energy, which reaches into HL rigid body ideas, and compares gradient with g.",
   "whereMarksAreLost": "Research design: the track is not truly circular so the model fails. Data analysis: T versus r is plotted without using R - r. Evaluation: slipping and rolling friction are ignored.",
   "dataNote": "Needs a curved track such as a bent rail or a shallow bowl and calipers; the uncertainty is the track shape and timing, so use many oscillations.",
   "verdict": "Neat because the prediction is precise, so you can test it. Check the track really is circular before starting, and expect the effect of r to be small but predictable."
  },
  {
   "id": "finding-the-fastest-pivot-on-a-swinging-rule",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Finding the fastest pivot on a swinging rule",
   "researchQuestion": "How does the distance d of the pivot from the centre of mass of a 1.00 m rule, varied from 0.05 m to 0.45 m in 0.05 m steps, affect its period for small oscillations?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Distance d of the pivot hole or clamp position from the centre, 0.05 m to 0.45 m in 0.05 m steps (9 values, 3 sets of 10 oscillations at each).",
   "dependentVariable": "Time for 10 oscillations with a stopwatch or phone video, divided by 10 to give T. Predicted T = 2π√((k² + d²)/(g d)), where k² = L²/12.",
   "controlledVariables": "Amplitude: small, below about 10°, set with a marked angle guide. Pivot friction: a knife edge or a thin nail through drilled holes. Ruler mass: the same rule with nothing attached. Plane of swing: guided to remain in one plane.",
   "physicsNeeded": "Physical pendulum T = 2π√(I/(mgd)), with I = m(k² + d²) by the parallel axis theorem. Plot T²d against d², the gradient is 4π²/g and the intercept is 4π²k²/g. The minimum period occurs at d = k.",
   "slVsHl": "SL: measure T against d, describe the minimum and compare with a simple pendulum. Top band: linearise to find g and k and check it against L/√12. The parallel axis theorem is an HL idea, but SL students can use it if it is derived.",
   "whereMarksAreLost": "Research design: only a few pivots, none close to the minimum. Data analysis: T² against d, which is not linear. Conclusion: no comparison of the predicted minimum. Evaluation: not addressing amplitude, and hole size affecting the pivot position.",
   "dataNote": "A metre rule with drilled holes and a stopwatch are enough; timing 10 swings keeps the human reaction uncertainty below 2%.",
   "verdict": "A solid classic with a clear model and a satisfying minimum. Add the linearisation and a value of g from the intercept to make it more than a period table."
  },
  {
   "id": "large-swing-angles-and-the-error-in-measured-g",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Large swing angles and the error in measured g",
   "researchQuestion": "How does the release angle of a simple pendulum, from 5° to 60° in 5 steps of 5° or more, change the value of g calculated from T = 2π√(L/g) with L = 1.000 m?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Release angle, 5°, 10°, 20°, 30°, 45°, 60° (6 values), measured with a protractor or from a photo, 3 repeats each.",
   "dependentVariable": "Time of 20 oscillations with a stopwatch or a light gate to get T, then g = 4π²L/T². Percentage difference from 9.81 m s⁻² calculated.",
   "controlledVariables": "Length from pivot to the centre of mass (measured with a metre rule and calipers). Bob mass and size. Pivot type (clamped between two blocks). Number of swings timed.",
   "physicsNeeded": "For small angles T = 2π√(L/g); for larger angles T ≈ T0(1 + θ²/16). Plot g calculated against θ², or T against θ², to show a linear rise in T and the point where the small angle approximation fails.",
   "slVsHl": "SL: show that g drifts as angle grows and compare to 9.81. Stronger: compare to the series correction and fit it, and use it to correct g at large angles.",
   "whereMarksAreLost": "Research design: too few large angles, or timing single oscillations. Data analysis: not propagating length and time uncertainty into g. Evaluation: ignoring damping over 20 swings.",
   "dataNote": "Needs a stopwatch, metre rule and a protractor; reaction time is the main uncertainty unless a light gate is used.",
   "verdict": "Common at school level but still strong when you fit a correction term and quantify it. Aim for the correction, not just the trend."
  },
  {
   "id": "magnetic-field-near-a-pendulum-bob-and-its-period",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Magnetic field near a pendulum bob and its period",
   "researchQuestion": "How does the current through a pair of Helmholtz coils (0 to 2.0 A, 6 or more values) affect the period of a pendulum with a magnetic bob swinging between them?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Coil current, 0 to 2.0 A in steps of 0.4 A, from a variable DC supply, with the current read on an ammeter. The field B is measured with a Hall probe at the bob position.",
   "dependentVariable": "Period from the time for 20 oscillations with video or a light gate, then T = t / 20. Repeat 3 times per current.",
   "controlledVariables": "Pendulum length, measured to the centre of the bob. Amplitude, no more than 5 degrees. Bob mass and magnet orientation. Coil temperature, by limiting run times, and distance from other magnetic material.",
   "physicsNeeded": "For a magnetic bob the extra force adds to the restoring force, so T = 2 pi sqrt(L / g_eff), with g_eff depending on B. If the bob is non-magnetic conductive, eddy damping appears instead. Plot 1 / T^2 against B, and look at the gradient as a measure of the magnetic effect. Note that a non-magnetic bob will show no change in period.",
   "slVsHl": "SL: measured period against B and a linear fit if a trend appears. Top band: build a force model for a bar magnet in a uniform field, checked by a Hall probe. Also test a steel or aluminium bob as control. No HL topic is needed.",
   "whereMarksAreLost": "Research design: not stating what bob material is used, since the effect depends on it. Data analysis: reporting no change in period without uncertainty analysis. Evaluation: forgetting that Helmholtz coil heating changes the current, and the field not being uniform near the edges.",
   "dataNote": "Needs a Helmholtz pair, a power supply, a Hall probe and a magnetic bob; the main uncertainty is that the effect on the period may be tiny.",
   "verdict": "Risky because a non-magnetic bob shows nothing, and voltage is a poor variable, so use current and measured field. Worth choosing only with a magnetic bob, where the result is a real physical effect."
  },
  {
   "id": "mass-spring-period-and-effective-spring-mass",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Mass-spring period and effective spring mass",
   "researchQuestion": "How does the period of a vertical steel spring oscillating with hanging masses from 0.100 kg to 0.500 kg vary with mass, and what spring constant and effective spring mass follow?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Hanging mass: 6 to 8 values from 0.100 to 0.500 kg in steps of 0.050 or 0.100 kg, with the period timed 3 times per mass. A second, optional set uses different numbers of coils (spring cut or springs in series or parallel).",
   "dependentVariable": "Time for 20 oscillations measured with a stopwatch, or with a motion sensor for a cleaner signal; period T is found by dividing, then T squared is calculated.",
   "controlledVariables": "Amplitude: fixed at about 2 cm and kept small. Same spring for the mass series. Release: vertical release without sideways motion. Starting position: timing from the centre of the oscillation using a fiducial marker.",
   "physicsNeeded": "T = 2 pi sqrt((m + m_s/3)/k). Plot T squared against m; the gradient is 4 pi squared over k and the horizontal intercept gives the effective spring mass. Compare k with a static extension test using Hooke's law.",
   "slVsHl": "SL students plot T squared against m and find k. Stronger work finds the intercept and connects it to a third of the spring mass, and checks k from static extension. HL depth could add damping analysis using a motion sensor.",
   "whereMarksAreLost": "Research design: two independent variables mixed together. Data analysis: reaction time on only 5 oscillations, and no linearisation. Evaluation: ignoring spring mass and non-vertical oscillation.",
   "dataNote": "Retort stand, spring, slotted masses and stopwatch; a motion sensor would improve timing, and the main uncertainty is human reaction time.",
   "verdict": "Well known and appears often, but the intercept for the spring mass and the static check give it extra depth. Keep one independent variable, mass, and treat the length as a separate follow-up only if you have time."
  },
  {
   "id": "oil-viscosity-and-damping-of-a-swinging-pendulum",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Oil viscosity and damping of a swinging pendulum",
   "researchQuestion": "How does the viscosity of a range of water and glycerol mixtures, from 1 mPa s to about 500 mPa s, affect the damping constant of a bob oscillating at small amplitude?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Glycerol fraction by volume in water: 0%, 20%, 40%, 60%, 80%, 100% (6 values). Viscosity is taken from published tables for the measured temperature, or found by a falling ball test.",
   "dependentVariable": "Amplitude of a pendulum with a submerged bob, filmed at 120 fps with a phone against a scale, and read over 10 or more oscillations. Damping constant is found from the gradient of ln(A) against time.",
   "controlledVariables": "Same bob, same string length and same immersed depth. Starting amplitude kept small, at about 5 degrees. Temperature of the liquid recorded with a thermometer, as viscosity changes strongly with it. Same container so the wall effects do not change.",
   "physicsNeeded": "Amplitude decays as A = A₀e^(−γt) for light damping, so ln(A) against t is a straight line with gradient −γ. Stokes drag on a small sphere is 6πηrv, so γ should increase with η at low speeds. Plot γ against η. At high damping the motion is no longer oscillatory, which is worth noting.",
   "slVsHl": "SL: measure γ for each mixture and plot γ against η, describing the trend. Top band: compare the gradient with the value predicted from Stokes' law and discuss where the Reynolds number makes it fail. HL depth: solve the damped oscillator equation and identify critical damping.",
   "whereMarksAreLost": "Research design: uncontrolled temperature, and viscosity values taken without matching them to the temperature. Data analysis: reading amplitude by eye without filming. Conclusion: claiming a linear relation when the data curve at low or high viscosity. Evaluation: ignoring drag on the string and buoyancy, which alter the effective mass.",
   "dataNote": "Needs glycerol, a tall container, a pendulum, a phone camera and a thermometer; the main uncertainty is the viscosity value at the actual temperature.",
   "verdict": "Ambitious but very rewarding. Measure the viscosity yourself with a falling sphere, so the whole investigation is your own data."
  },
  {
   "id": "pendulum-period-when-the-string-wraps-round-a-peg",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Pendulum period when the string wraps round a peg",
   "researchQuestion": "How does the distance d of a fixed peg below the pivot, varied from 0.10 m to 0.60 m in steps of 0.10 m on a 0.80 m string, affect the period of a pendulum whose string catches on the peg at the bottom of its swing?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Peg distance d below the pivot: 0.10, 0.20, 0.30, 0.40, 0.50 and 0.60 m (6 values), with the total string length fixed at 0.80 m. Ten timed sets of 10 oscillations at each value.",
   "dependentVariable": "Full period T of the two-part swing, found by timing 10 oscillations with a stopwatch or a phone video analysed frame by frame (or a light gate), then dividing by 10. Compared with the period predicted from the two effective lengths L and (L minus d).",
   "controlledVariables": "Bob mass and size: same steel sphere throughout. Release angle: kept at 8 degrees using a printed protractor sheet and a clamp stop. Total string length: measured with a metre rule from pivot to bob centre each time. Peg diameter: one thin rod used for all runs, so the wrapping radius does not change.",
   "physicsNeeded": "For small angles T = 2π√(L/g). With a peg, half the swing has length L and half has length (L minus d), so T = π√(L/g) + π√((L−d)/g). Plot T against √(L−d) and check for a straight line with gradient π/√g and intercept π√(L/g). Compare g from the gradient with 9.81 m s⁻².",
   "slVsHl": "SL students can time the swing, plot the linear graph and get g with an uncertainty. Top band work checks the small angle assumption by repeating at two amplitudes and explains any offset from the peg radius. HL depth can come from deriving the two-part period model, discussing how the string bending on the peg changes the effective length, and estimating the correction from the finite bob size.",
   "whereMarksAreLost": "Research design: choosing large release angles so the small angle formula fails, or failing to keep the total length fixed. Data analysis: ignoring the uncertainty in timing and plotting T against d, which is not linear. Conclusion: not comparing the measured curve with the derived model quantitatively. Evaluation: not addressing friction at the peg, the string thickness and the bob's finite size, which all shift the results systematically.",
   "dataNote": "Needs a retort stand, thread, a steel bob, a thin rod and a stopwatch or phone; the main uncertainty is reaction time, reduced by timing 10 swings and repeating.",
   "verdict": "A neat twist on the standard pendulum because the prediction is not a simple power law, so it invites real modelling. Make it yours by testing the model prediction at each peg position and explaining why the residuals look the way they do. The original idea of pivot geometry was vague, and this is the closest measurable version."
  },
  {
   "id": "period-of-a-torsion-pendulum-against-mass-radius",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "HL",
   "title": "Period of a torsion pendulum against mass radius",
   "researchQuestion": "How does the distance r of two 100 g masses from the axis (2 to 12 cm, six values) affect the period of a torsional oscillator made from a disc on a steel wire?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Radial position of two identical masses placed symmetrically on the disc: 2, 4, 6, 8, 10, 12 cm from the centre (six values), repeated three times.",
   "dependentVariable": "Period T from timing 10 oscillations with a stopwatch or a phone video, with T² then calculated for each radius.",
   "controlledVariables": "Wire (same length and clamp); mass of each added body (weigh both); angular displacement (start at about 20°, small enough to stay linear); disc and hanging mechanism (unchanged throughout).",
   "physicsNeeded": "T = 2π√(I/κ) with I = I₀ + 2mr². Plot T² against r²: gradient = 8π²m/κ and the intercept gives 4π²I₀/κ. The torsion constant κ follows from the gradient.",
   "slVsHl": "Rotational moment of inertia is HL (A.4), so this suits HL best. An SL student would need heavy guidance. Top band: compare κ from the gradient with an independent estimate, for example from the wire's shear modulus and dimensions.",
   "whereMarksAreLost": "Research design: masses not placed symmetrically or radius measured to the mass edge instead of its centre. Data analysis: forgetting the non-zero intercept from the disc's own inertia. Evaluation: not checking damping or a change of κ with large twist.",
   "dataNote": "Needs a steel wire, clamp, disc with marked radii and masses; the main uncertainty is timing and the position of each mass.",
   "verdict": "Worth choosing if you have the apparatus, because the linear T² against r² graph is clean and the intercept gives you something to interpret. Building the rig is the hard part, so test it early."
  },
  {
   "id": "suspension-wire-thickness-and-the-decay-rate-of-a-pendulum",
   "topic": "C.1",
   "topicName": "Simple harmonic motion",
   "level": "both",
   "title": "Suspension wire thickness and the decay rate of a pendulum",
   "researchQuestion": "How does the diameter of a copper suspension wire (0.20 to 1.00 mm, 5 values) affect the damping constant of a 0.50 m pendulum?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Wire diameter from 0.20 to 1.00 mm, 5 gauges, checked with a micrometer at several points on each wire. Three swings sets per gauge.",
   "dependentVariable": "Amplitude against time from phone video and a protractor board, or a light gate for the period; the damping constant is the gradient of ln(A) against t.",
   "controlledVariables": "Same bob mass and shape; wire length fixed at 0.50 m; starting angle 10 degrees; same clamp and same room, avoiding draughts.",
   "physicsNeeded": "For light damping A = A0 exp(-gamma t). Plot ln(A) against t, gamma equals minus the gradient. Thicker wires dissipate more energy through bending and clamp losses, so compare gamma with diameter (perhaps d^4 for bending stiffness).",
   "slVsHl": "SL students find gamma for each wire and plot it against diameter. Top band work proposes a bending stiffness model and considers whether wire or clamp is dominating.",
   "whereMarksAreLost": "Research design: thicker wire also alters mass and stiffness, mixing several effects. Data analysis: amplitude is read from video too coarsely. Evaluation: clamp friction is not separated from wire effects.",
   "dataNote": "Needs a micrometer and several wire gauges; damping from a wire is very small, so long runs are needed and the uncertainty is large.",
   "verdict": "Ambitious, and the effect may be hidden behind air drag and clamp friction. Take it on only if you can run for several minutes per trial; otherwise the data will be noise."
  },
  {
   "id": "foam-and-fabric-layers-reducing-sound-level",
   "topic": "C.2",
   "topicName": "Wave model",
   "level": "both",
   "title": "Foam and fabric layers reducing sound level",
   "researchQuestion": "How does the number of layers N of acoustic foam (N = 0 to 8 layers, each 1.0 cm thick) placed between a 1000 Hz speaker and a sound level meter affect the intensity received at 0.50 m?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Number of foam layers N, 0, 1, 2, 4, 6, 8, five recordings each.",
   "dependentVariable": "Sound level in dB from a sound level meter or a calibrated phone app, converted to intensity using I = I0 × 10^(L/10). Ratio I / I(N=0) is then calculated.",
   "controlledVariables": "Frequency: a fixed 1000 Hz tone from a signal generator. Speaker output: same amplitude setting. Distances: fixed with a ruler and clamps. Room: same quiet room, background noise measured before each set and subtracted.",
   "physicsNeeded": "Attenuation of intensity follows I = I0 e^(−μx), so plot ln(I/I0) against thickness x. The gradient gives −μ, the attenuation coefficient. Links to intensity and the inverse square law from C.2.",
   "slVsHl": "Suitable for SL. To reach the top band an SL student tests whether the exponential model holds, compares frequencies of 500, 1000 and 2000 Hz, and treats reflections and leakage around the sample edges.",
   "whereMarksAreLost": "Research design: several materials and thicknesses varied at once so no clear IV. Data analysis: averaging dB values instead of converting to intensity first. Evaluation: phone microphone calibration and automatic gain not discussed.",
   "dataNote": "A signal generator, speaker and either a sound meter or phone with a calibrated app are needed; automatic gain control in phones and room reflections are the main uncertainties.",
   "verdict": "Worth choosing if you narrow it to one material and test an exponential model. Comparing many materials at once gives thin analysis. Check the phone app against a proper meter."
  },
  {
   "id": "light-transmission-through-stacked-glass-slides",
   "topic": "C.2",
   "topicName": "Wave model",
   "level": "both",
   "title": "Light transmission through stacked glass slides",
   "researchQuestion": "How does the transmitted light intensity change as the number of identical glass slides in a stack increases from 1 to 8?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Number of identical glass microscope slides in the stack, 1 to 8 (8 values), 3 repeats each.",
   "dependentVariable": "Light intensity reading in lux from a light sensor or a photodiode voltage behind the stack, in a dark room. Transmission fraction is calculated as I/I₀ with no slides.",
   "controlledVariables": "Same lamp with a stabilised supply. Fixed distance from lamp to sensor. Room made dark and background reading subtracted. Slides cleaned and kept parallel and normal to the beam.",
   "physicsNeeded": "Exponential attenuation I = I₀e^(−μx) and, with reflection at each surface, a per slide transmission factor. Plot ln(I/I₀) against number of slides; the gradient gives the loss per slide, including reflection and absorption together.",
   "slVsHl": "SL students plot transmission against slide count and identify the pattern. Top band work separates reflection loss from absorption, using the intercept and a test with different colour filters or a laser.",
   "whereMarksAreLost": "Research design: not separating reflection from absorption and calling it all absorption. Data analysis: ignoring background light. Conclusion: claiming an exponential relationship without a good fit. Evaluation: not discussing lamp drift or multiple reflections between slides.",
   "dataNote": "Lux meter or light sensor, lamp and slides; the main uncertainty is stray light and lamp drift.",
   "verdict": "A good clean investigation if you handle reflection. That distinction is the twist that separates a good report from a naive one."
  },
  {
   "id": "sound-intensity-loss-through-air-against-frequency-200-to-1000-hz",
   "topic": "C.2",
   "topicName": "Wave model",
   "level": "both",
   "title": "Sound intensity loss through air against frequency, 200 to 1000 Hz",
   "researchQuestion": "How does the fall in sound intensity level over a 0.5 m to 3.0 m path change with source frequency between 200 Hz and 1000 Hz in steps of 200 Hz?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Frequency of a loudspeaker driven by a signal generator: 200, 400, 600, 800, 1000 Hz (5 values). For each, measure at 6 distances from 0.5 m to 3.0 m. Three repeats.",
   "dependentVariable": "Sound level from a calibrated sound meter or phone app with an external microphone, in dB. Convert to intensity I = I₀·10^(L/10), then find the extra loss beyond the inverse square law from the slope of a fit.",
   "controlledVariables": "Output amplitude: fixed generator setting, checked at 0.5 m at each frequency. Room: same room and position, away from walls, to cut reflections. Speaker and microphone height and orientation: fixed on stands. Background noise: measured and subtracted, tests done when quiet.",
   "physicsNeeded": "Intensity I = P/(4πr²) in free space, plus a possible exponential attenuation I = I₀e^(−αr). Plot ln(I r²) against r; the gradient is −α. Compare α at each frequency. Over a few metres in air, α at these frequencies is tiny, so the result is likely to be near zero and dominated by room effects.",
   "slVsHl": "SL: get the inverse square law working at each frequency and comment on any difference. Top band: extract α with uncertainty, show honestly whether it differs from zero, and explain standing waves and reflections as the main systematic error.",
   "whereMarksAreLost": "Research design: indoor reflections and speaker frequency response mimic an attenuation effect. Data analysis: dB averaged as if linear. Conclusion: claiming absorption where it is a room effect. Evaluation: not testing the microphone response at each frequency.",
   "dataNote": "Needs a signal generator, speaker and reasonable microphone, ideally outdoors; the main uncertainty is that real air absorption at these frequencies is far below room effects.",
   "verdict": "Risky as worded because air absorption over metres is negligible. Better twist: replace the air with foam, cloth or a tube of absorbing material, where attenuation is measurable and varies clearly with frequency."
  },
  {
   "id": "sound-level-from-a-speaker-over-distance",
   "topic": "C.2",
   "topicName": "Wave model",
   "level": "both",
   "title": "Sound level from a speaker over distance",
   "researchQuestion": "How does the sound intensity from a speaker playing a 1 kHz tone change with distance between 0.50 m and 4.00 m, in 8 steps?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Distance from the speaker to a sound level meter, 0.50 to 4.00 m in 8 values, measured with a tape; 3 readings each, outdoors or in a large hall.",
   "dependentVariable": "Sound level in dB from a calibrated meter, converted to intensity using I = I0 × 10^(L/10) with I0 = 10⁻¹² W m⁻².",
   "controlledVariables": "Signal generator amplitude and frequency fixed. Speaker height and meter height the same, away from walls and floor. Background noise measured and kept low. Meter orientation fixed pointing at the speaker.",
   "physicsNeeded": "For a point source I = P/(4πr²), so plot I against 1/r², or L against log₁₀ r with expected gradient -20 dB per decade. The gradient gives the exponent.",
   "slVsHl": "SL students convert dB to intensity and plot a straight line. Top band work deals with reflections, the near field of a speaker and the meter's uncertainty, and fits an offset in r. HL depth can add the effect of absorption.",
   "whereMarksAreLost": "Research design: reflections from walls and floor, unaddressed. Data analysis: averaging dB values instead of intensities. Conclusion: claiming exact inverse square without uncertainty. Evaluation: a speaker not being a point source at close range.",
   "dataNote": "Needs a sound level meter or a calibrated phone app and a large open space; the main uncertainty is echoes and background noise.",
   "verdict": "Easy but the trap is reflections. Do it outdoors on a field and compare to a run indoors as a twist."
  },
  {
   "id": "sound-speed-in-water-as-it-warms",
   "topic": "C.2",
   "topicName": "Wave model",
   "level": "both",
   "title": "Sound speed in water as it warms",
   "researchQuestion": "How does the speed of ultrasound in water change as its temperature rises from 10 °C to 60 °C in steps of 10 °C?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Water temperature, 10 to 60 °C in 6 values, set with ice and a kettle and read on a digital thermometer; each value repeated three times.",
   "dependentVariable": "Time delay of an ultrasound pulse between a transmitter and receiver, read on an oscilloscope, divided into a fixed path length measured with a ruler to get speed.",
   "controlledVariables": "Transducer separation fixed by a clamped rig. Water volume and container the same each time. Water kept stirred so temperature is uniform, and readings taken as it cools slowly. Same water purity, using distilled water throughout.",
   "physicsNeeded": "v = d/t for the pulse. Plot v against temperature; expect a rise of roughly 3 m/s per °C near room temperature, so the gradient can be compared with literature. Link to the bulk modulus and density: v = √(K/ρ).",
   "slVsHl": "SL students plot v against T and describe the trend with uncertainties. Top band work compares the measured gradient to tabulated values, and considers the curvature seen above 50 °C. Beyond that, propagate the uncertainty on d and t through to v.",
   "whereMarksAreLost": "Research design: choosing a solid without a workable method, or too small a temperature range. Data analysis: timing uncertainty from the oscilloscope cursors not propagated. Conclusion: no comparison with accepted values. Evaluation: not addressing the temperature gradient in the water while it cools.",
   "dataNote": "Needs an ultrasound pair and an oscilloscope or data logger; the main uncertainty is a short path length giving a small time delay.",
   "verdict": "A liquid is far more practical than a solid here. Use a path of at least 0.30 m so the timing error stays small."
  },
  {
   "id": "sunscreen-layer-thickness-and-uv-transmission",
   "topic": "C.2",
   "topicName": "Wave model",
   "level": "both",
   "title": "Sunscreen layer thickness and UV transmission",
   "researchQuestion": "How does the mass of sunscreen spread per unit area, from 0.5 to 3.0 mg cm⁻², affect the fraction of UV light transmitted through a clear acrylic sheet?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Sunscreen applied per unit area, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 mg cm⁻² (6 values), weighed on a balance, with 3 sheets at each value.",
   "dependentVariable": "UV intensity behind the sheet from a UV sensor or a UV index meter, with transmission calculated as I/I₀ against a clean sheet. UV transmission of the acrylic itself checked first.",
   "controlledVariables": "Same UV lamp at a fixed distance and same warm up time. Same brand of sunscreen. Same acrylic sheet type and area. Spread evenly with a fixed method. Dark room with a background reading taken.",
   "physicsNeeded": "Beer Lambert law I = I₀e^(−μx). Plot ln(I/I₀) against mass per area; the gradient gives an attenuation coefficient. Compare with what the SPF 30 label predicts, since SPF 30 implies roughly 3% transmission at 2 mg cm⁻².",
   "slVsHl": "SL students plot transmission against layer and describe the trend. Top band work linearises, extracts μ, tests the label's claim, and comments on non uniform films.",
   "whereMarksAreLost": "Research design: thickness is not measurable directly, so no justification of mass per area. Data analysis: uneven films giving big scatter that is ignored. Conclusion: overclaiming SPF accuracy. Evaluation: not considering that the sensor may respond to a different band from UVB.",
   "dataNote": "Needs a UV sensor and a precise balance; the main uncertainty is spreading an even film and the sensor's spectral response.",
   "verdict": "Interesting but harder than it looks. Use UV safe practice with a low power lamp, and only choose it if your school has a UV sensor."
  },
  {
   "id": "tray-depth-and-ripple-speed-in-shallow-water",
   "topic": "C.2",
   "topicName": "Wave model",
   "level": "both",
   "title": "Tray depth and ripple speed in shallow water",
   "researchQuestion": "How does the water depth h, varied from 0.5 cm to 3.0 cm in steps of 0.5 cm, affect the speed of surface waves in a ripple tray, measured in cm/s?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Water depth in a ripple tray: 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 cm (6 values), each measured with a ruler or depth gauge at several points and repeated 3 times.",
   "dependentVariable": "Wave speed v = f × λ. Frequency f is read from a strobe or the vibrator setting, or from a slow motion phone video. Wavelength λ is measured from a still image with a ruler in the frame, using ten wavelengths and dividing by ten.",
   "controlledVariables": "Vibrator frequency, held on a fixed setting and checked with a strobe or video. Water temperature, checked with a thermometer before each run. Tray levelled with a spirit level. Same dipper depth and amplitude each time.",
   "physicsNeeded": "For shallow water v = √(g h), so v² against h should be a straight line through the origin with gradient g. Students can also plot v against √h. Deep water breaks the relation, which is worth discussing.",
   "slVsHl": "SL: measure v at each depth, plot v² against h and compare the gradient with 9.81. Top band, SL or HL: test where the shallow water limit fails by comparing h with λ, and account for surface tension and the meniscus. HL depth could come from the dispersion relation for all depths.",
   "whereMarksAreLost": "Research design: depth not measured reliably across a tray that is not level. Data analysis: too few wavelengths measured, so large uncertainty in λ. Conclusion: claiming v ∝ h without testing the power law. Evaluation: ignoring that the shallow water condition fails at the larger depths.",
   "dataNote": "Needs a ripple tray or a large clear tray with a vibrator, a strobe or phone camera; the main uncertainty is reading λ from a moving pattern.",
   "verdict": "A sound, low cost choice if you are careful about levelling and freezing the pattern. Make it yours by showing the depth at which the √h law stops working."
  },
  {
   "id": "slinky-pulse-speed-and-a-length-that-should-not-matter",
   "topic": "C.2",
   "topicName": "Wave model",
   "level": "both",
   "title": "Slinky pulse speed and a length that should not matter",
   "researchQuestion": "How does the speed of a longitudinal pulse on a metal Slinky change as it is stretched from 2.0 m to 5.0 m, and is the travel time really independent of length as the wave model predicts?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 0,
   "independentVariable": "Stretched length of the Slinky lying on a smooth floor or table, from 2.0 m to 5.0 m in 0.5 m steps (7 values), with 5 pulses timed at each length.",
   "dependentVariable": "Time for a longitudinal pulse to travel from one end to the other, measured frame by frame from a 240 fps phone video with a metre rule in view. The pulse speed is the stretched length divided by that time.",
   "controlledVariables": "Same Slinky and the same fixed end throughout. Pulse started with a similar small push each time, so the coils never touch. Slinky lying flat on a low friction surface, checked by the pulse arriving with the same shape. Camera fixed and perpendicular to the Slinky.",
   "physicsNeeded": "A stretched spring carries longitudinal waves at v = L√(k/M), where L is the stretched length, k the spring constant and M the total mass. So the travel time t = L/v = √(M/k) should not depend on the length at all. Plot v against L: the prediction is a straight line through the origin with gradient √(k/M). Measure k separately by hanging masses on the Slinky and compare the two values of k.",
   "slVsHl": "SL students plot v against L, find the gradient with its uncertainty and compare k with the value from hanging masses. For the top band, test where the model fails: at short lengths the coils touch and the relation breaks, and friction on the floor damps the pulse. HL students can compare a longitudinal pulse with a transverse one on the same Slinky.",
   "whereMarksAreLost": "Research design: pulses so large that coils collide, or a floor with enough friction to slow the pulse. Data analysis: timing by eye instead of by frames, and no uncertainty on the frame count. Conclusion: stating that time is constant without testing it against the scatter of the data. Evaluation: ignoring that the end coils are not ideal and that the mass is not uniform.",
   "dataNote": "Needs only a metal Slinky, a tape measure, a phone with slow motion video and a set of slotted masses; the main uncertainty is the frame at which the pulse arrives.",
   "verdict": "My own idea, not listed on any site, and one of the few IAs where the physics predicts something surprising that you can check in an afternoon. It is cheap, safe and personal if you add the independent measurement of k."
  },
  {
   "id": "refractive-index-of-sugar-solutions-as-a-concentration-probe",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Refractive index of sugar solutions as a concentration probe",
   "researchQuestion": "How does the refractive index of sugar solution measured with a laser and a semicircular tank change for sugar mass fractions from 0 to 40% in 5% steps, and how precisely can the method identify an unknown concentration?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 4,
   "independentVariable": "Sugar mass fraction 0, 5, 10, 15, 20, 25, 30, 35, 40% (9 values), 3 measurements of the angle pair at each.",
   "dependentVariable": "Angles of incidence and refraction measured with a laser and protractor on a semicircular transparent tank, or the critical angle for total internal reflection. Refractive index calculated from Snell's law.",
   "controlledVariables": "Room temperature recorded for each run. Same laser wavelength. Solutions weighed on a balance and fully dissolved and stirred. Same tank position and ray entering along the radius so it is not refracted at the curved face.",
   "physicsNeeded": "n1 sin θ1 = n2 sin θ2. Plot sin θ1 against sin θ2 for each solution; the gradient gives n. Then plot n against mass fraction, expected close to linear from 1.333 to about 1.40. Use the line to find an unknown solution.",
   "slVsHl": "SL students get n for each solution and a calibration line. To reach the top band, propagate angle uncertainty into n and show the sensitivity, then test the method on a soft drink of unknown sugar content and compare with the label. HL adds nothing specific.",
   "whereMarksAreLost": "Research design: small change in n means a protractor may not resolve differences. Data analysis: uncertainty in n not propagated. Conclusion: no statement of what precision the method reaches. Evaluation: temperature and dissolving not addressed.",
   "dataNote": "Needs a laser, a semicircular tank and a protractor; angle reading (about ±0.5°) limits how small a concentration change can be seen.",
   "verdict": "Overdone (listed on 4 sites), but the twist of testing it as a measuring method and checking a drink label makes it yours. Do that rather than only plotting n against concentration."
  },
  {
   "id": "testing-malus-s-law-with-a-rotating-analyser-and-a-light-sensor",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Testing Malus's law with a rotating analyser and a light sensor",
   "researchQuestion": "How does the transmitted intensity of light through two polarising filters vary as the analyser is rotated from 0° to 180° in 10° steps, and does it follow I = I₀cos²(θ − θ₀)?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 4,
   "independentVariable": "Analyser angle, 0° to 180° in 10° steps (19 values), read from a protractor mount. Three full rotations to give repeats.",
   "dependentVariable": "Light intensity read by a light sensor or a phone lux app, or the voltage from a photodiode across a load resistor. Calculate I/I₀ after subtracting background light.",
   "controlledVariables": "Source: LED torch or lamp on a stabilised supply, fixed distance. Room darkened and the dark reading subtracted. Sensor fixed in place. Polariser angle fixed at a set position.",
   "physicsNeeded": "Malus's law: I = I₀cos²θ. Plot I against cos²(θ − θ₀) for a straight line through the origin with gradient I₀. Leave the offset θ₀ as a fitted parameter instead of assuming alignment. The residuals show any leakage from imperfect filters.",
   "slVsHl": "SL students can do the cos² plot and a gradient. To reach the top band, fit θ₀ and a minimum intensity, and discuss non-ideal polarisers. HL adds nothing needed, though an extension with a third filter at 45° is a good check.",
   "whereMarksAreLost": "Research design: too few angles near the minima, or stray light not controlled. Data analysis: no uncertainty in angle, forgetting the background subtraction. Conclusion: saying the law is confirmed from a graph look without a quantitative fit. Evaluation: ignoring sensor saturation, LED drift and the source being partly polarised. Also note this is a very common topic, so examiners expect something extra.",
   "dataNote": "Polaroid sheets, a light sensor and a protractor are enough; the main uncertainty is lamp drift and stray light, plus a 1 to 2° angle reading.",
   "verdict": "Very popular, seen by examiners many times, so a plain version will score average. Twist: use a third filter between crossed ones and predict the intensity, or compare filters at different wavelengths with coloured LEDs."
  },
  {
   "id": "angular-width-of-the-central-maximum-for-single-slit-diffraction",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Angular width of the central maximum for single-slit diffraction",
   "researchQuestion": "How does the width of a single slit (0.05 to 0.40 mm, 6 values) affect the angular half-width of the central maximum of a 650 nm laser pattern?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Slit width, 0.05 to 0.40 mm, six or more values from a calibrated slit slide or adjustable slit, checked by a microscope or scale. Measure each pattern three times.",
   "dependentVariable": "Distance across the central maximum on a screen measured with a ruler or on a photo with a scale, giving the angle by arctan of half the width over the slit to screen distance L.",
   "controlledVariables": "Laser wavelength, the same laser for all runs. Slit to screen distance, fixed at about 2 to 3 m. Room darkened. Laser beam perpendicular to the slit and screen.",
   "physicsNeeded": "First minimum at a sin θ = λ. For small angles θ ≈ λ/a. Plot θ (y) against 1/a (x). The gradient is λ, which can be compared with the laser label value, e.g. 650 nm.",
   "slVsHl": "SL students can plot θ against 1/a and compare the gradient to λ. Higher marks come from separating the width of the central maximum from the fuzzy edges, using a light sensor scan to locate minima, and checking small angle validity. HL gives no extra syllabus but intensity profile analysis with sinc² is a strong extension.",
   "whereMarksAreLost": "Research design: slit width not verified, so a stated width is trusted. Data analysis: reading the edge of a blurry maximum, without uncertainty. Conclusion: not comparing the gradient with the known wavelength. Evaluation: not discussing the two supplied ideas as effectively one; systematic error in L and laser safety not addressed.",
   "dataNote": "Needs a laser (class 2), slits and a long dark room; the main uncertainty is locating the dim edge of the maximum, about 1 to 2 mm.",
   "verdict": "Good, clean physics and easy to do, but the relationship is well known, so aim to extract the wavelength and check the slit widths yourself. Twist: use a single hair or a wire of measured diameter as the obstacle."
  },
  {
   "id": "colour-dependence-of-refractive-index-in-a-glass-prism",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Colour dependence of refractive index in a glass prism",
   "researchQuestion": "How does the refractive index of a glass prism vary across five wavelengths from about 450 nm to 650 nm, and does a Cauchy relation n = A + B/λ² fit the results?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Wavelength of light, 5 to 6 values (for example violet 405 nm, blue 450 nm, green 532 nm, red 650 nm laser diodes, or filtered lamp lines), 3 repeats of the deviation measurement each.",
   "dependentVariable": "Angle of minimum deviation D, read on a spectrometer table or protractor sheet to 0.1 to 0.5 degrees. Refractive index is calculated from n = sin((A+D)/2) / sin(A/2), with the prism angle A measured separately.",
   "controlledVariables": "Prism angle: measure A once with the same method. Prism position on the table: mark its outline. Beam alignment: keep the beam horizontal and at the same height. Temperature and prism material: use one prism throughout.",
   "physicsNeeded": "n = sin((A+D)/2)/sin(A/2), plus Cauchy's n = A + B/λ². Plot n against 1/λ²; the gradient is B and the intercept A. Linearity shows whether the model holds over the range.",
   "slVsHl": "SL students compare n at each colour and plot n against 1/λ². Top band requires propagating the angle uncertainty into n and asking whether the differences between colours are larger than that uncertainty. HL adds the group velocity view or a second dispersion formula.",
   "whereMarksAreLost": "Research design: laser safety and alignment ignored, or wavelengths that are not actually known. Data analysis: differences in n (about 0.01) smaller than the uncertainty, with no propagation. Evaluation: not commenting on the finite beam width and on a mislocated minimum deviation.",
   "dataNote": "Needs a prism, several laser pointers or filters and a rotating table; the largest uncertainty is locating minimum deviation to within about 0.5 degrees.",
   "verdict": "A neat, honest investigation if the wavelengths are truly known. Use a long lever arm to a wall so the deviation angle is small in uncertainty; that is where the mark is won."
  },
  {
   "id": "deviation-of-a-ray-through-a-glass-prism",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Deviation of a ray through a glass prism",
   "researchQuestion": "How does the angle of deviation of a red laser ray through a 60° glass prism vary as the angle of incidence is changed from 30° to 70° in steps of 5°, and what is the refractive index from the minimum deviation?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Angle of incidence i on the first face, 9 values from 30° to 70°, each repeated 3 times.",
   "dependentVariable": "Angle of deviation D measured on a large protractor or from a marked paper sheet with the laser ray traced. The refractive index is calculated from the minimum deviation.",
   "controlledVariables": "Prism: same 60° prism, with the apex angle measured first. Wavelength: same laser, checked from its label. Laser position: fixed on the rotating table and aligned at the centre. Room temperature: stable, and prism kept clean.",
   "physicsNeeded": "Snell's law n = sin i / sin r, and n = sin((A + D_min)/2) / sin(A/2). Plot D against i, a curve with a minimum. Alternatively plot sin i against sin r for the first face, gradient is n. Both values of n can be compared.",
   "slVsHl": "SL students plot sin i against sin r and compare n. Top band work fits the minimum deviation curve, measures A, and repeats with two colours to show dispersion. HL students can add total internal reflection at the second face.",
   "whereMarksAreLost": "Research design: the original dependent variable, the refraction angle, is ambiguous inside a prism, so it must be defined. Data analysis: reading angles by eye with no uncertainty. Conclusion: not relating n to the accepted value. Evaluation: ignoring the finite width of the ray.",
   "dataNote": "A laser, a prism, a protractor and paper are enough, and the main uncertainty is the thickness of the ray when marking angles.",
   "verdict": "Simple and many students do it, so it needs a twist. Add colours by using several lasers to compare n by wavelength, and be careful to define the angle you measure."
  },
  {
   "id": "diffraction-gratings-and-the-precision-of-wavelength-values",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Diffraction gratings and the precision of wavelength values",
   "researchQuestion": "How does the line density of a grating (100, 300, 600 and 1000 lines per mm) affect the percentage uncertainty in the wavelength of the green mercury line?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Grating line density, 4 to 5 gratings from 100 to 1000 lines/mm; measure orders 1 and 2 for each, 3 repeats.",
   "dependentVariable": "Diffraction angle from the position of the spot on a screen and grating to screen distance (tan θ = x/L), giving λ = d sin θ / n. Percentage uncertainty in λ is calculated by propagating the errors from x and L.",
   "controlledVariables": "Light source: use the same laser or a single spectral tube. Grating to screen distance: fix it at 1.00 m and check with a rule. Grating perpendicular to the beam: align by looking at the reflection back on the source. Reading method: the same ruler and same person.",
   "physicsNeeded": "n λ = d sin θ, with d = 1/N. Plot sin θ against n for each grating; the gradient is λ/d. Compare uncertainty against line density to see whether higher density gives a smaller percentage error.",
   "slVsHl": "SL students compare uncertainties for each grating and explain the result. For the top band, discuss why the higher orders are lost for fine gratings (sin θ cannot exceed 1) and the trade-off. HL can compute the resolving power N·m and test it on a closely spaced pair such as the sodium doublet.",
   "whereMarksAreLost": "Research design: the question mixes precision with resolving power and is not focused. Data analysis: assuming the stated line density is exact. Evaluation: not checking the zero-order alignment or a systematic error in L.",
   "dataNote": "Needs several gratings, a laser or spectral lamp and a metre rule; the resolving-power part is only possible with a discharge lamp and a good spectrometer.",
   "verdict": "Good if you drop the resolving-power claim unless you have the sodium doublet to test. Keep to one clear question: which grating gives the lowest percentage uncertainty."
  },
  {
   "id": "focal-length-and-magnification-of-thin-lenses",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Focal length and magnification of thin lenses",
   "researchQuestion": "How does the image distance, for a converging lens with a marked focal length of 10 cm, vary as the object distance is changed from 15 cm to 40 cm in steps of 5 cm, and what focal length and magnification result?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Object distance u, 6 values from 15 to 40 cm on an optical bench, repeated 3 times. The extension is to use 3 lenses of different power.",
   "dependentVariable": "Image distance v found by sharpest image on a screen, with ruler. Focal length is calculated from the lens equation and magnification from m = v/u, checked by measuring image height.",
   "controlledVariables": "Object: same illuminated arrow or cross wire. Alignment: lens, object and screen on the same axis at the same height. Lens aperture: same for all runs. Room light: dimmed so the sharp image is clear.",
   "physicsNeeded": "Thin lens equation 1/f = 1/u + 1/v. Plot 1/v against 1/u, a straight line with intercept 1/f and gradient −1. Magnification m = v/u. Compare f with the value marked on the lens or a distant object method.",
   "slVsHl": "SL students get f from the linear graph. Top band work quantifies the depth of focus as the main uncertainty, corrects for the lens thickness, and compares three lenses. Extending to a combination of two lenses adds depth.",
   "whereMarksAreLost": "Research design: lens type is categorical and has too few values for a graph. Data analysis: not accounting for the range of positions where the image seems sharp. Conclusion: comparing f only to the label. Evaluation: not mentioning spherical aberration.",
   "dataNote": "An optical bench, lenses and a screen are enough, and the main uncertainty is judging the sharpest image.",
   "verdict": "Fine but very common. Make it personal by testing a lens with a different medium such as a water-filled lens, or a two lens system."
  },
  {
   "id": "focal-length-of-concave-mirrors-of-different-radius",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Focal length of concave mirrors of different radius",
   "researchQuestion": "How does the radius of curvature R of five concave mirrors (R from 20 cm to 100 cm) affect the measured focal length and the image magnification at a fixed object distance of 1.5 times each mirror's focal length?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Radius of curvature of the mirror, five or six values, using different mirrors or a flexible mirror sheet bent to known curvature. R measured with a spherometer or by a template.",
   "dependentVariable": "Image distance found by moving a screen until the image is sharp, three repeats each, measured with a metre rule. Focal length from the mirror equation, and magnification from image height over object height.",
   "controlledVariables": "Object size, using the same illuminated cross-wire. Mirror aperture kept small by a mask to reduce spherical aberration. Mirror aligned along the optical axis. Room dimmed for a consistent judgement of sharpness.",
   "physicsNeeded": "1/u + 1/v = 1/f and f = R/2. Plot f against R, expected gradient 0.5. Also plot 1/v against 1/u for one mirror to get f from the intercept.",
   "slVsHl": "SL students confirm f = R/2 and check magnification equals v/u. Deeper work measures the depth-of-focus uncertainty and the effect of aperture on the focus position.",
   "whereMarksAreLost": "Research design: a fixed object distance in metres will not suit all mirrors, so scale it to f. Data analysis: uncertainty in judging the sharpest image is often ignored. Evaluation: spherical aberration is rarely discussed.",
   "dataNote": "You need several mirrors with known radius, which is the hard part; the sharpness judgement gives about 1 to 2 cm uncertainty.",
   "verdict": "Workable only if you can get five different mirrors. The twist is to use one bendable mirror or shiny spoons, and to study aperture effects."
  },
  {
   "id": "focal-length-of-lenses-against-lens-curvature",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Focal length of lenses against lens curvature",
   "researchQuestion": "How does the focal length of thin glass or acrylic lenses depend on the radius of curvature of their surfaces, for radii from 5 cm to 25 cm, using the lens maker's relationship?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Radius of curvature of the lens surface (5 cm to 25 cm, at least 5 lenses), found with a spherometer or from lens data; the lenses are all plano-convex of the same material.",
   "dependentVariable": "Focal length f, found by focusing a distant window image or by an illuminated object on a screen, measured with a metre rule; each lens measured three times.",
   "controlledVariables": "Lens material: all lenses from the same set and of the same refractive index. Lens diameter: similar, checked with calipers. Light source: same bright lamp and object slit. Method of focusing: same person judges sharpest image, from both sides.",
   "physicsNeeded": "For a thin plano-convex lens, 1/f = (n − 1)/R. Plot 1/f (y) against 1/R (x): the gradient is (n − 1), giving the refractive index. Linear image formation 1/f = 1/u + 1/v can be used to find f.",
   "slVsHl": "SL: a linear plot and n from the gradient. Top band: a spherometer measurement of R with propagated uncertainty, and a comment on the thick lens and spherical aberration. Magnification adds little, so I would drop it and focus on f.",
   "whereMarksAreLost": "Research design: getting lenses with a range of R is hard, and the reason for the choice of 1/f against 1/R is not stated. Data analysis: uncertainty in f is large because the sharpest image is a range, and this is usually ignored. Conclusion: the n found is not compared with the value for the material. Evaluation: not dealing with the thick lens and spherical aberration.",
   "dataNote": "Needs a set of plano-convex lenses of different curvature, a spherometer or calipers and an optical bench; getting a spread of R is the main problem.",
   "verdict": "Worth it only if the school owns lenses with different radii, so check first. The twist is measuring n and comparing it with the material, rather than only listing the results."
  },
  {
   "id": "fringe-count-against-mirror-displacement-in-a-michelson-interferometer",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "HL",
   "title": "Fringe count against mirror displacement in a Michelson interferometer",
   "researchQuestion": "How does the number of fringes counted in a Michelson interferometer depend on the displacement of the movable mirror, from 0 to 50 µm, and what laser wavelength does this give?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Displacement of the movable mirror, set with a micrometer screw (0 to 50 µm in steps of 5 µm, 10 values, repeated 3 times); a further run may tilt the mirror to change the incidence angle and the fringe spacing.",
   "dependentVariable": "Number of fringes N passing a reference mark, counted by eye or from video at 60 fps; wavelength λ = 2Δd/N is calculated.",
   "controlledVariables": "Laser: same laser pointer at about 650 nm. Alignment: mirrors and beam splitter fixed in place and screwed to a rigid base. Vibrations: rig on a heavy table, no walking near while counting. Lever ratio: calibrated for the micrometer if a lever is used.",
   "physicsNeeded": "For mirror displacement Δd, N = 2Δd/λ. Plot N (y) against Δd (x): the gradient is 2/λ. Interference needs path differences, which are in HL wave content; the setup uses superposition. The angle of incidence changes the fringe ring radius, since a path difference 2d cos θ.",
   "slVsHl": "Mostly HL because of the interference and path difference treatment. An SL student can do a Young's double-slit experiment instead. Top band: compare λ with the laser specification, treat the counting error and the micrometer calibration.",
   "whereMarksAreLost": "Research design: the input idea uses the incident angle as the IV, which is hard to control and measure, so I switched it to displacement. Data analysis: fringe counts lost when the pattern moves fast. Conclusion: not comparing λ with the manufacturer value. Evaluation: vibrations and backlash in the micrometer are not described.",
   "dataNote": "Needs an interferometer kit or a home-built one with a laser and beam splitter; alignment and vibrations are the main issues.",
   "verdict": "Only realistic if your school has an interferometer, since alignment is hard. Very impressive when it works, but the original angle of incidence idea is not practical, so I would use displacement."
  },
  {
   "id": "fringe-spacing-against-screen-distance-for-a-laser-double-slit",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Fringe spacing against screen distance for a laser double slit",
   "researchQuestion": "How does the fringe spacing from a 650 nm laser passing through a double slit change as the screen distance is varied from 0.80 m to 3.00 m in 8 steps, and what slit separation does this give?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Slit to screen distance D, 0.80 to 3.00 m in 8 values, measured with a tape; 3 fringe measurements at each distance.",
   "dependentVariable": "Fringe spacing s measured across 10 fringes with a ruler or callipers on the screen, divided by the number of gaps; slit separation d then calculated from the gradient.",
   "controlledVariables": "Laser wavelength, using the same laser, checked on the label or a grating. Same double slit slide, unchanged. Laser beam perpendicular to the slit and screen, checked by aligning. Room dimmed so fringes are sharp.",
   "physicsNeeded": "s = λD/d. Plot s against D, expecting a straight line through the origin with gradient λ/d, so d = λ/gradient. Compare to the slit spacing stated on the slide or measured under a microscope.",
   "slVsHl": "SL students plot s against D and find d from the gradient. Top band work compares d with the manufacturer's value, uses the uncertainty of the gradient, and evaluates the small angle approximation. Note that the slit separation is fixed, so the RQ should ask about fringe spacing rather than about spacing changing with distance.",
   "whereMarksAreLost": "Research design: a wording that treats slit spacing as the variable. Data analysis: measuring one fringe rather than across many. Conclusion: a comparison with the stated d without uncertainty. Evaluation: not discussing fringe blur at large distances.",
   "dataNote": "Needs a laser, a double slit slide and a metre rule; the main uncertainty is locating fringe centres.",
   "verdict": "Very common but very clean. Reword the RQ around fringe spacing and add a measurement of d by a second method to make it yours."
  },
  {
   "id": "fringe-spacing-against-slit-separation-with-a-laser",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Fringe spacing against slit separation with a laser",
   "researchQuestion": "How does the slit separation d, varied from 0.10 mm to 0.50 mm in six steps, affect the fringe spacing on a screen 2.0 m from a 650 nm laser?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Slit separation d, 6 values from 0.10 to 0.50 mm using a multi-slit slide or printed or blade-made slits; 3 fringe measurements each.",
   "dependentVariable": "Distance across 10 fringes measured with a ruler or a calliper on a photograph with a scale, divided by 10 to give the fringe spacing s. Slit separation is checked with a travelling microscope or a scanned image if not marked.",
   "controlledVariables": "Slit to screen distance D: fix at 2.00 m with a metre rule and lock the bench. Wavelength: use one laser and record its stated value. Screen tilt: keep it perpendicular to the beam. Room darkness: dim the lights for every measurement.",
   "physicsNeeded": "s = λD/d. Plot s against 1/d; a straight line through the origin with gradient λD. Compare λ from the gradient with the stated value.",
   "slVsHl": "SL students do the 1/d graph and compare the wavelength found. To reach the top band, test whether the small-angle approximation holds and use the uncertainty in the gradient. HL depth can include the single-slit envelope.",
   "whereMarksAreLost": "Research design: fringes too close at large d so they cannot be resolved. Data analysis: measuring one fringe not several, giving large percentage uncertainty. Conclusion: not comparing the extracted wavelength with the manufacturer's value.",
   "dataNote": "Needs a laser, double-slit slide and metre rule; uncertainty is dominated by how well the fringe centres can be located, which is about 0.5 mm.",
   "verdict": "A classic and safe, so it is only worth choosing if you add a twist such as self-made slits and a check on slit spacing. Expect examiners to have seen the standard version."
  },
  {
   "id": "fringe-spacing-from-a-double-slit-at-several-wavelengths",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Fringe spacing from a double slit at several wavelengths",
   "researchQuestion": "How does the fringe spacing on a screen 2.00 m from a double slit vary with the wavelength of the light, using lasers of at least 3 wavelengths and slit separations of 0.15 to 0.50 mm?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Slit separation d, using 5 double slits (for example 0.15, 0.25, 0.30, 0.40 and 0.50 mm), with a single laser. A second run with red, green and violet lasers uses one slit pair.",
   "dependentVariable": "Fringe spacing measured across 10 fringes with a metre rule or by photographing the pattern beside a scale. Spacing is found by dividing the total by the number of fringe gaps.",
   "controlledVariables": "Screen distance: fixed at 2.00 m and measured with a tape. Laser wavelength (in the slit-separation run): same laser. Slit width: use a commercial multi-slit slide. Alignment: laser perpendicular to the slides, checked with a reflection.",
   "physicsNeeded": "The double slit fringe spacing is s = λD/d. Plot s (y) against 1/d (x); gradient = λD, giving λ to compare with the laser label. For wavelength, plot s against λ with gradient D/d.",
   "slVsHl": "SL students verify the relation and find the wavelength. Stronger work also considers the single-slit envelope and its effect on missing orders. Wave-particle duality needs photon counting, so be clear that this only shows the wave side; the link to duality is HL-level discussion (E.2).",
   "whereMarksAreLost": "Research design: the RQ as originally phrased is about duality, which a school double slit cannot test. Data analysis: measuring one fringe rather than many and not propagating uncertainty. Safety: laser class not discussed.",
   "dataNote": "Needs laser pointers, a multi-slit slide and a metre rule; the main uncertainty is locating fringe centres.",
   "verdict": "Very standard, so it will not stand out unless you go deeper. Reframe it away from duality and make the twist a comparison of three wavelengths with an accurate diffraction grating check."
  },
  {
   "id": "fringe-spacing-in-young-s-double-slit-for-different-colours",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Fringe spacing in Young's double slit for different colours",
   "researchQuestion": "How does the fringe spacing on a screen 2.0 m away depend on the wavelength of light, using lasers or LEDs with wavelengths from about 405 nm to 650 nm through a fixed double slit?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Wavelength of the source, 5 values from 405 nm to 650 nm using different lasers or filtered sources with known labels, each measured 3 times.",
   "dependentVariable": "Fringe spacing measured over 10 fringes on the screen with a ruler and divided by 10 to reduce error. Wavelength is calculated from the spacing.",
   "controlledVariables": "Slit separation: same double slit slide, value from the label or checked. Slit to screen distance: fixed with a tape measure. Alignment: laser perpendicular to the slits and screen. Room: dark, screen at the same position.",
   "physicsNeeded": "w = λD/s. Plot fringe spacing w against λ, a straight line through the origin, with gradient D/s. From the gradient the slit separation s can be found and compared. Small angle approximation is valid.",
   "slVsHl": "SL students verify the linear relation and compare with labelled values. Top band work takes s from the gradient and compares it with a microscope measurement, and discusses the small angle approximation and laser wavelength tolerances. HL students can add single slit envelope effects.",
   "whereMarksAreLost": "Research design: laser wavelengths are only 3 or 4 values, so the graph is thin. Data analysis: measuring a single fringe gap rather than many. Conclusion: not using the gradient for s. Evaluation: not addressing laser safety and fringe blur.",
   "dataNote": "Needs a double slit slide, several lasers, a metre rule and a dark room, and the main uncertainty is locating the centre of each fringe.",
   "verdict": "Very standard and many students have done it, so it needs a personal twist. Add a comparison with a diffraction grating, or use a range of colour LEDs with a narrow slit for more wavelengths. Note that it is interference, not diffraction only."
  },
  {
   "id": "grating-diffraction-with-tilted-incidence",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "HL",
   "title": "Grating diffraction with tilted incidence",
   "researchQuestion": "How does the angle of incidence θi, from 0° to 50° in 10° steps, change the angular position of the first-order maximum for a 600 lines per mm grating lit by a 650 nm laser?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Angle of incidence on the grating, six values, set on a rotating stage or protractor base.",
   "dependentVariable": "Position of the first-order maximum on a screen 1.50 m away, measured with a metre rule, three repeats. Deviation angle from trigonometry. Relative brightness with a light sensor as an optional extra.",
   "controlledVariables": "Laser wavelength, using the same diode and checking with normal incidence. Same grating and its orientation. Grating to screen distance, fixed with a clamp. Room darkened.",
   "physicsNeeded": "d(sinθm - sinθi) = mλ. Plot sinθm against sinθi, expected gradient of 1 and intercept of λ/d. Use it to find the wavelength.",
   "slVsHl": "Oblique incidence goes beyond the standard normal incidence formula, so it fits HL depth. SL students can attempt it if they derive the path difference clearly.",
   "whereMarksAreLost": "Research design: intensity is hard to measure and should be dropped or treated separately. Data analysis: sign convention for angles on each side of the normal. Evaluation: alignment errors of the incident angle.",
   "dataNote": "Needs a laser, grating and a rotating stage; the main uncertainty is aligning the zero angle to about 1°.",
   "verdict": "A good twist on a very common grating experiment. Choose it if you like geometry, and derive the modified equation yourself."
  },
  {
   "id": "laser-wavelength-from-michelson-fringe-counting",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Laser wavelength from Michelson fringe counting",
   "researchQuestion": "What is the wavelength of a red laser pointer found by counting fringes as one mirror of a Michelson interferometer is moved through 0.05 mm to 0.30 mm using a micrometer screw?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Mirror displacement d, 6 values from 0.05 to 0.30 mm, set with a micrometer drive, each repeated 3 times.",
   "dependentVariable": "Number of fringes N passing a marked point, counted by eye or on video. Wavelength is calculated from λ = 2d/N.",
   "controlledVariables": "Laser: same source, warmed up for 10 minutes so the output is stable. Vibration: bench on foam or a solid table, no walking. Beam alignment: fixed after set up, only the micrometer moved. Temperature and air draughts: room closed and mirror not touched.",
   "physicsNeeded": "Path difference changes by 2d, so N = 2d/λ. Plot N against d, a straight line through the origin with gradient 2/λ. Comparing λ with the value given for the laser checks the method. The speed of light cannot be found from this alone, since c needs the frequency too, so the question should be about wavelength.",
   "slVsHl": "SL students count fringes and get λ from the gradient. Top band work uses a video to count large N, estimates the mirror drive calibration error, and possibly measures the refractive index of air by changing the pressure in a cell. HL students can add coherence length.",
   "whereMarksAreLost": "Research design: the original question claims c but a Michelson setup with a laser gives wavelength only. Data analysis: miscounting fringes with no uncertainty on N. Conclusion: not comparing to the manufacturer wavelength range. Evaluation: ignoring backlash in the micrometer.",
   "dataNote": "Needs a Michelson kit or a home built one with a beam splitter and mirrors, and the main uncertainty is the micrometer backlash and vibration.",
   "verdict": "Impressive if your school owns the kit, but c is not the outcome, so change the RQ to wavelength. The twist is to use the same setup on a second laser colour."
  },
  {
   "id": "law-of-reflection-tested-on-plane-curved-and-rough-mirrors",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "SL",
   "title": "Law of reflection tested on plane, curved and rough mirrors",
   "researchQuestion": "How closely does the measured angle of reflection agree with the angle of incidence for a plane mirror, for angles from 10 to 70 degrees in 10 degree steps?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Angle of incidence, 10 to 70 degrees in 7 steps, set with a ray box and a protractor sheet; repeat each 3 times, and use a second surface such as a curved mirror or brushed metal as a comparison.",
   "dependentVariable": "Angle of reflection, found by tracing the ray on paper with pins or a laser line, and measured with a protractor; compute the difference between the two angles.",
   "controlledVariables": "Same laser or ray box and the same distance to the mirror; mirror pivot fixed at the origin of the protractor; normal drawn with a set square; room dimmed to see the ray clearly.",
   "physicsNeeded": "Law of reflection: θr = θi. Plot θr against θi; the gradient should be 1 and the intercept 0. The size of the residuals shows the uncertainty of the method.",
   "slVsHl": "SL: a straight-line fit and comparing the gradient with 1. Top band: the analysis has to go beyond the law, for example measuring the beam spread for a rough surface, or a rotating mirror that doubles the deflection.",
   "whereMarksAreLost": "Research design: the question has a known answer, so there is little scope for personal inquiry. Data analysis: only 3 or 4 angles and no uncertainty. Evaluation: a large protractor reading error not addressed.",
   "dataNote": "Needs a laser pointer or ray box, a mirror and a protractor; the main uncertainty is reading the angle to about 1 degree.",
   "verdict": "Too basic as it stands, since everyone knows the answer. Only worth it if you replace the plane mirror with a curved surface or a rotating mirror and measure the scatter."
  },
  {
   "id": "line-spacing-of-gratings-and-the-angles-of-laser-maxima",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Line spacing of gratings and the angles of laser maxima",
   "researchQuestion": "How does the line density of a diffraction grating (100, 300, 600, 1000 lines/mm and other available values) affect the angle of the first-order maximum for a 650 nm red laser?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Grating line density, at least five values from 100 to 1000 lines/mm, or use several gratings and different laser colours as extra data.",
   "dependentVariable": "Distance between the central and first-order spots on a screen measured with a metre rule at a known grating to screen distance of about 1.5 m, calculating θ = arctan(y/D). Also the width of each spot to comment on sharpness.",
   "controlledVariables": "Laser wavelength kept by using the same laser. Grating to screen distance D fixed and measured. Grating perpendicular to the beam, checked by the reflected spot. Room dark and same screen.",
   "physicsNeeded": "d sinθ = nλ. Plot sinθ against lines per mm (1/d), gradient = nλ. Compare gradient with known wavelength, or use the graph to find λ. Sharpness increases with the number of illuminated slits N.",
   "slVsHl": "SL students can obtain λ from the gradient with uncertainty and comment on higher orders. For top band, use several orders and check the small angle approximation fails at high line density. HL work could add resolving power with the illuminated N.",
   "whereMarksAreLost": "Research design: 'sharpness' is not measured, so use spot width or intensity with a light sensor. Data analysis: using tanθ ≈ sinθ at large angles. Evaluation: laser wavelength not verified and beam not centred.",
   "dataNote": "Needs a laser pointer, gratings and a metre rule; the main uncertainty is reading the centre of a wide spot at the screen.",
   "verdict": "A reliable, common idea, so give it a personal angle. Twist: measure an unknown item such as a CD or a feather, or find the wavelength of a green laser that you own."
  },
  {
   "id": "loudness-minima-spacing-from-two-loudspeakers-and-wavelength",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Loudness minima spacing from two loudspeakers and wavelength",
   "researchQuestion": "How does the spacing y between adjacent sound minima, measured along a line 2.0 m from two speakers, change with speaker separation d from 0.20 m to 0.60 m in 5 steps at 1.5 kHz?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Speaker separation d: 0.20, 0.30, 0.40, 0.50, 0.60 m (5 values), each measured with a metre rule.",
   "dependentVariable": "Minima spacing y found by moving a microphone (phone or data logger sensor) along a taped line and marking the quietest points, 3 runs each. Calculate wavelength λ = yD/d and compare with v/f.",
   "controlledVariables": "Frequency, from one signal generator feeding both speakers in parallel. Distance D from speaker plane to the scan line, fixed at 2.0 m. Speaker amplitude, matched by equal volume settings. Room, chosen to have soft surfaces or done outdoors to reduce reflections.",
   "physicsNeeded": "Double-source interference: y = λD/d. Plot y against 1/d. The gradient is λD, so λ = gradient/D, then speed v = fλ.",
   "slVsHl": "SL students confirm the inverse relation and derive v. Top work checks the small-angle approximation, measures the residual loudness at minima to show unequal amplitudes, and quantifies reflections by repeating in two rooms.",
   "whereMarksAreLost": "Research design: strong reflections in a small room that fill in the minima. Data analysis: reporting minima positions with no uncertainty when the minimum is broad. Evaluation: not commenting on unequal speaker output.",
   "dataNote": "Needs two speakers, a generator and a microphone app; minima are broad, so position uncertainty is often ±2 cm.",
   "verdict": "Good if you do it carefully, since it is a sound version of double slits. Choosing a controlled room and quantifying reflections will separate you from the pack."
  },
  {
   "id": "magnification-of-a-converging-lens-against-object-distance",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Magnification of a converging lens against object distance",
   "researchQuestion": "How does the linear magnification of a converging lens of focal length 10 cm change as the object distance goes from 12 cm to 40 cm?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Object distance u, from 12 to 40 cm in about 8 values, set on an optical bench; three readings for each with the screen re-focused.",
   "dependentVariable": "Image height on a screen measured with a ruler, and image distance v measured with a metre rule; calculate the magnification m = h_i/h_o and v/u.",
   "controlledVariables": "Same lens and object, such as an illuminated cross-wire of 2.0 cm; the lens and object axes aligned at the same height; darkened room; the screen adjusted to the sharpest image each time, using a consistent judging method.",
   "physicsNeeded": "Thin lens equation 1/u + 1/v = 1/f and m = -v/u = f/(u - f). Plot 1/m against u; the gradient is 1/f and the intercept is -1, so f can be extracted. Alternatively plot 1/v against 1/u.",
   "slVsHl": "SL: the graph of m against u with a linearised version, and a comparison of f with the nominal value. Top band: analyse the uncertainty from the focusing, and the effect of lens thickness or aberration on the results.",
   "whereMarksAreLost": "Research design: the sharpness of the image is subjective and a single reading is taken. Data analysis: plotting m against u and calling it a fit without linearising. Evaluation: not noting the position of the lens's principal plane.",
   "dataNote": "Needs an optical bench, a lens and a screen; the main uncertainty is locating the sharpest focus, about 1 to 2 cm.",
   "verdict": "A safe choice that scores well if you linearise and estimate f carefully. Add a second lens or a lens combination to make it more personal."
  },
  {
   "id": "malus-s-law-with-crossed-polarising-filters-at-varied-angles",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Malus's law with crossed polarising filters at varied angles",
   "researchQuestion": "How does the light intensity transmitted through a second polarising filter vary as it is rotated from 0° to 180° in 15° steps relative to the first?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Angle between transmission axes of two polarisers, 0° to 180° in 15° steps (13 values), measured on a protractor mount, with three readings each.",
   "dependentVariable": "Intensity from a light sensor or lux meter (or phone light sensor) in a dark enclosure, with dark background subtracted (lux).",
   "controlledVariables": "Light source: stabilised LED at fixed distance and supply voltage. Ambient light: shielded and background recorded. Sensor position and distance: clamped. Filters: same pair throughout, with the first fixed.",
   "physicsNeeded": "Malus's law: I = I₀cos²θ. Plot I against cos²θ: a straight line through the origin, with gradient I₀. Extension: unpolarised light through one filter and reflected polarisation at Brewster's angle (HL-level content is not required).",
   "slVsHl": "SL: I against cos²θ and check of linearity. Top band: fit a residual background term, discuss imperfect extinction, and add a third filter at 45° to test the famous surprise result.",
   "whereMarksAreLost": "Research design: the original wording about the incidence angle affecting polarisation is unclear; the measurable quantity is filter angle. Data analysis: ignoring background light. Conclusion: no quantified agreement with cos²θ. Evaluation: source drift and sensor saturation.",
   "dataNote": "Two polarising sheets, a lux meter or phone sensor and a dark box are enough; the main uncertainty is stray light and angle reading.",
   "verdict": "Easy to run and gives a clean linear graph, but easy to reduce to a trivial lab. Add the three-filter test or reflection from a table or water surface to make it your own."
  },
  {
   "id": "measuring-a-hair-s-thickness-from-a-laser-diffraction-pattern",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Measuring a hair's thickness from a laser diffraction pattern",
   "researchQuestion": "What is the width of a strand of my hair, found from the diffraction minima of a 650 nm laser at slit-to-screen distances of 1.0 to 4.0 m?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Distance from hair to screen, 1.0 to 4.0 m in 7 values, with the hair held taut on a frame. Repeat with hairs from three different people if available.",
   "dependentVariable": "Distance between the n-th minima measured with a ruler on the screen; calculate the hair width from d = n lambda D / y and compare with a micrometer reading.",
   "controlledVariables": "Laser wavelength checked from the label; hair position fixed in the beam; darkened room; screen kept perpendicular to the beam.",
   "physicsNeeded": "Babinet's principle gives the same minima as a single slit of the same width: a sin(theta) = n lambda. Plot the fringe spacing against D; gradient equals lambda/a, so a = lambda/gradient.",
   "slVsHl": "SL students calculate a from one clear pattern and repeat it. Top band work uses several D values and several minima, propagates uncertainty in the gradient and validates against a micrometer.",
   "whereMarksAreLost": "Research design: the question has no independent variable, so a range of distances must be built in. Data analysis: small angle approximation is not justified. Evaluation: fringe edges are hard to place and the hair is not straight or uniform.",
   "dataNote": "Needs a laser pointer, ruler and a room with 4 m of space; the uncertainty is where the minima sit, so measure across many fringes.",
   "verdict": "A classic but sound one, and a real chance to get a validated result against a micrometer. Making distance the independent variable, and testing hair from several people or several places, turns it into a proper investigation."
  },
  {
   "id": "measuring-a-laser-wavelength-with-several-gratings",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Measuring a laser wavelength with several gratings",
   "researchQuestion": "What is the wavelength of a red laser pointer, in nm, when measured from the diffraction orders of gratings with 100, 300 and 600 lines per mm, and does the value agree across the gratings?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Order number n = 1 to 5 where visible, for three gratings (100, 300, 600 lines/mm), and also grating to screen distance at 5 values from 0.5 m to 2.5 m. Each spot position is measured 3 times.",
   "dependentVariable": "Spot distance from the central maximum measured with a metre rule or a taped scale, giving angle θ = arctan(x/L). Wavelength is found from the gradient of sin θ against n.",
   "controlledVariables": "Same laser, switched on and warmed up for a few minutes. Grating held perpendicular to the beam using reflection back to the source. Screen perpendicular to the beam. Room dimmed the same way each time.",
   "physicsNeeded": "d sin θ = nλ. Plot sin θ against n; the gradient is λ/d, so λ = gradient × d. Compare with the manufacturer's stated value.",
   "slVsHl": "SL: one grating, a few orders, a single value of λ with uncertainty. Top band: compare several gratings and check consistency, and address the fact that grating spacing is only quoted approximately, perhaps by calibrating it with a laser of known wavelength. HL adds nothing syllabus wise, but depth comes from the uncertainty analysis.",
   "whereMarksAreLost": "Research design: a question that only asks for a known value with no real test. Data analysis: using small angle approximations at large angles. Conclusion: agreement with the stated wavelength without a percentage difference against uncertainty. Evaluation: not considering grating tolerance or beam alignment.",
   "dataNote": "Needs a laser pointer, gratings, a rule and a screen; the main uncertainty is locating the centre of each bright spot and the grating's stated spacing.",
   "verdict": "Easy data but a very familiar question. Build in a real test, such as calibrating one grating with a second laser or checking two lasers against each other, to make it worth marks."
  },
  {
   "id": "newton-s-rings-radius-and-the-wavelength-of-light",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Newton's rings radius and the wavelength of light",
   "researchQuestion": "How does the radius of the nth dark Newton's ring (n = 1 to 10) depend on n for a plano-convex lens of known focal length under sodium light, and what wavelength does this give?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Ring number n from 1 to 10 (10 values), measured on each side of the centre, 3 repeats of the full set.",
   "dependentVariable": "Ring diameter measured with a travelling microscope to 0.01 mm, halved to give radius r. The wavelength comes from the gradient of r² against n.",
   "controlledVariables": "Lens radius of curvature R: measure it with a spherometer or from the focal length. Light source: use one sodium lamp, allowed to warm up. Pressure on the lens: keep the clamp unchanged. Microscope movement direction: always move one way to avoid backlash.",
   "physicsNeeded": "r² = nλR for dark rings when the centre is dark. Plot r² against n; gradient is λR. Check the value of λ against 589 nm.",
   "slVsHl": "SL students plot r² against n and compare the wavelength. For the top band, treat the imperfect contact at the centre by using D_n² − D_m² so that the offset cancels. HL depth can add a change of the medium (a water layer) and the effect on λ.",
   "whereMarksAreLost": "Research design: R not measured independently, so λ is circular. Data analysis: n miscounted because the centre spot is not dark. Evaluation: ignoring the offset from dust or lens deformation.",
   "dataNote": "Needs a travelling microscope, sodium lamp, plano-convex lens and glass plate; the largest error is counting rings and locating edges.",
   "verdict": "A precise and unusual choice, better than the wedge because the data give many points. Use the diameter difference method and you have a strong analysis story."
  },
  {
   "id": "reflected-colour-and-thickness-of-soap-film-interference",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "HL",
   "title": "Reflected colour and thickness of soap-film interference",
   "researchQuestion": "How does the reflected intensity from a soap film at near-normal incidence vary with film thickness as the film drains, measured over 60 s with a 650 nm laser diode?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Film thickness changing with drainage time, sampled every 2 s over 60 s (30 values), with three films; a second run with angle of incidence 0°, 15°, 30°, 45°, 60°.",
   "dependentVariable": "Reflected intensity from a light sensor or phone video of pixel brightness (arbitrary units), plotted against time or angle, with fringe counts.",
   "controlledVariables": "Wavelength: one laser diode or filtered LED. Film frame: same vertical wire loop and soap solution mix. Air draughts: enclosure. Detector distance and position: clamped.",
   "physicsNeeded": "Path difference 2nt cosθ_r with a half-wave phase change at the front surface: maxima when 2nt cosθ_r = (m + ½)λ. Plot fringe order m against 1/cosθ_r or count fringes against angle to test the relation and estimate n or thickness.",
   "slVsHl": "Interference from thin films is HL-only, so SL students should choose two-source or diffraction instead. HL top band: fit for film thickness, compare with a wedge model and discuss the change in thickness as the film thins.",
   "whereMarksAreLost": "Research design: original wording is unclear and thin film thickness is not directly controlled. Data analysis: no calibrated intensity scale. Conclusion: weak comparison with theory. Evaluation: evaporation, film instability and drift.",
   "dataNote": "Needs a laser, a stable vertical film and a light sensor; the main uncertainty is unknown, changing thickness.",
   "verdict": "Only for HL students who like optics and can tolerate messy data. An air-wedge between two glass slides is a much more controllable version of the same physics."
  },
  {
   "id": "reflected-intensity-of-p-polarised-light-and-brewster-s-angle",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "HL",
   "title": "Reflected intensity of p-polarised light and Brewster's angle",
   "researchQuestion": "How does the angle of incidence (20 to 80 degrees, steps of 5) affect the reflected intensity of p-polarised laser light from a glass slab, and at what angle does it reach a minimum?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Angle of incidence from 20 to 80 degrees in 5 degree steps (13 values), set on a rotating turntable with a protractor and a polariser fixed to give p-polarisation.",
   "dependentVariable": "Reflected intensity from a light sensor or LDR behind an aperture, normalised to the incident beam reading; calculate reflectivity R and the refractive index from tan(theta_B) = n.",
   "controlledVariables": "Same laser and power; polariser orientation fixed; darkened room with background subtracted; detector distance and aperture fixed.",
   "physicsNeeded": "At Brewster's angle p-polarised light is not reflected, and tan(theta_B) = n. Plot R against angle and locate the minimum, then compare n with a value from Snell's law.",
   "slVsHl": "Polarisation is core wave content but the Fresnel treatment goes past SL. An SL student can find the minimum and calculate n; the top band compares against Fresnel equations.",
   "whereMarksAreLost": "Research design: alignment of the polarisation axis is not checked with a second polariser. Data analysis: R from a sensor uncalibrated for non linear response. Evaluation: reflections from the back surface of the slab are not removed.",
   "dataNote": "Needs a laser, polariser, turntable and a light sensor; the uncertainty is the angle setting and sensor linearity.",
   "verdict": "Great if you have the kit, since the minimum is sharp and gives n. Use a black backed glass slab to avoid the second reflection."
  },
  {
   "id": "reflected-laser-intensity-from-transparent-blocks-of-varying-refractiv",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Reflected laser intensity from transparent blocks of varying refractive index",
   "researchQuestion": "How does the refractive index n of a transparent medium (n = 1.33 to 1.60, six materials) affect the fraction of a laser beam reflected at normal incidence, measured as a ratio of light sensor readings?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Refractive index of six media: water, acrylic, glass, and sugar or glycerol solutions of known concentration in a flat-sided tank. Measure n first with a separate Snell's law setup. Three repeats each.",
   "dependentVariable": "Reflected intensity divided by incident intensity, from a light sensor (or a photodiode with a voltmeter) placed in the reflected beam, after subtracting the dark reading.",
   "controlledVariables": "Angle of incidence kept near 0 degrees using a marked baseline and protractor; laser power checked against the incident reading before each run; room lit constant or blacked out with a card tunnel; sensor distance fixed with a clamp.",
   "physicsNeeded": "Fresnel result at normal incidence: R = ((n2 - n1)/(n2 + n1))^2, which is beyond the syllabus but can be quoted. Plot measured R against ((n-1)/(n+1))^2, gradient should be about 1. Snell's law (C.3) gives n.",
   "slVsHl": "SL students compare R with the predicted trend and state the discrepancy. Top band work handles the second surface reflection from the back of the block, uses polarised light, or extends to Brewster angle.",
   "whereMarksAreLost": "Research design: back-surface reflection contaminating the reading and no dark correction. Data analysis: R is only a few percent, so uncertainty is large and often ignored. Evaluation: laser drift and stray light not quantified.",
   "dataNote": "Needs a laser, light sensor and clear blocks or tanks; reflected fractions of 2 to 5 percent are small, so background and laser stability dominate the uncertainty.",
   "verdict": "Interesting but harder than it looks because the signals are tiny. Worth it if you make the block thick or angled to separate the two reflections and can justify using the Fresnel formula."
  },
  {
   "id": "refractive-index-and-critical-angle-of-transparent-blocks",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Refractive index and critical angle of transparent blocks",
   "researchQuestion": "How do the refractive indices of acrylic, glass, and sugar solutions (0% to 40% by mass in 10% steps) compare when found from angles of incidence 10° to 60°, and how do the predicted critical angles agree with the measured ones?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Angle of incidence from 10° to 60° in 10° steps, for each medium, with material as the comparison between acrylic, glass and four sugar solution concentrations in a semicircular tank.",
   "dependentVariable": "Angle of refraction read on a ray box and a protractor, three repeats. Refractive index from the gradient of sin i against sin r. Critical angle found by turning the block until the ray just disappears, and compared with arcsin(1/n).",
   "controlledVariables": "Wavelength, using a red laser or a single colour filter. The ray always aimed at the centre of the flat face of the semicircular block. Same protractor and reading position. Solution temperature at room level.",
   "physicsNeeded": "Snell's law, n = sin i / sin r, and sin θc = 1/n. Plot sin i against sin r, where the gradient is n. Compare the critical angle with 1/n.",
   "slVsHl": "SL students find n and compare the critical angle. Extra depth comes from linking sugar concentration to n, quantifying the gradient uncertainty, and discussing dispersion.",
   "whereMarksAreLost": "Research design: unspecified wavelength and measurement method. Data analysis: uncertainty in a protractor of ±1° for the critical angle. Evaluation: rays not through the centre.",
   "dataNote": "Blocks, laser, protractor and a semicircular tank are enough; angle reading uncertainty of about 1° is the limit.",
   "verdict": "Very common, so it needs a twist. The sugar concentration series gives a clear trend and makes it more personal than comparing blocks."
  },
  {
   "id": "refractive-index-of-liquids-from-a-hollow-prism",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Refractive index of liquids from a hollow prism",
   "researchQuestion": "What is the refractive index of sugar solutions with mass concentrations from 0% to 40% in 10% steps, found from the minimum deviation angle in a hollow prism?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Sugar concentration in water, 0, 10, 20, 30 and 40 % by mass (5 values), each made up on a balance and each measured 3 times.",
   "dependentVariable": "Angle of minimum deviation D read on a spectrometer table or from a ray trace on paper; refractive index n calculated from the prism formula.",
   "controlledVariables": "Same hollow prism of known apex angle A, measured with the spectrometer; monochromatic light from a laser or a sodium lamp; temperature of the liquid measured with a thermometer; the prism faces cleaned and thin so that the glass effects are negligible.",
   "physicsNeeded": "n = sin((A + D)/2) / sin(A/2). Plot n against concentration; the gradient shows how solution density changes the index. Alternatively use Snell's law at a single face and plot sin i against sin r, with the gradient giving n.",
   "slVsHl": "SL: n for each solution, a graph of n against concentration and a comparison with data tables. Top band: work out the uncertainty in n from the angle errors, and compare with the Lorentz-Lorenz link to density.",
   "whereMarksAreLost": "Research design: the dependent variable is unclear, since the refraction angle changes with the incident angle, so use minimum deviation. Data analysis: no uncertainty propagation to n. Evaluation: not noting leaks, temperature drift and finding the minimum by eye.",
   "dataNote": "Needs a hollow prism, a spectrometer or a laser with a protractor, and a balance; the main uncertainty is locating the minimum deviation to about 0.5 degrees.",
   "verdict": "A strong idea once the IV becomes concentration, since the liquid type gives no continuous variable. Check your n values against tabulated data for sucrose to give a clear evaluation."
  },
  {
   "id": "ripple-tank-slit-diffraction-in-salt-solutions-of-varying-density",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Ripple tank slit diffraction in salt solutions of varying density",
   "researchQuestion": "How does the density of a sodium chloride solution (1000 to 1150 kg m^-3, 6 values) affect the half-angle of the central diffracted wavefront behind a 2.0 cm slit in a ripple tank?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Density of salt solution, 1000 to 1150 kg m^-3 in steps of 30, mixed by mass and checked with a hydrometer or a measuring cylinder and balance. Three repeat runs per value.",
   "dependentVariable": "Diffraction half-angle from a stroboscope or phone slow-motion photo of the wavefronts, measured with a protractor on a printout, plus wavelength from the same image. Calculate sin(theta) and compare with lambda/b.",
   "controlledVariables": "Slit width fixed by the same barriers; dipper frequency fixed by the motor supply voltage; liquid depth kept at 5 mm with a ruler; temperature checked with a thermometer.",
   "physicsNeeded": "Single slit: sin(theta) = lambda/b. Wave speed in shallow liquid depends on depth and on surface tension, so density changes wavelength at fixed frequency. Plot sin(theta) against lambda (gradient 1/b), or lambda against density.",
   "slVsHl": "SL students measure angle and wavelength and test lambda/b. Top band work explains why the effect is small, compares with shallow water theory and treats surface tension as a hidden variable.",
   "whereMarksAreLost": "Research design: density changes surface tension and viscosity too, so the variable is not isolated. Data analysis: angles are hard to read on blurred wavefronts and the uncertainty is ignored. Evaluation: a very small trend is claimed as real without comparing it with the spread of repeats.",
   "dataNote": "Needs a ripple tank with strobe or a camera; the main uncertainty is locating the edge of the diffracted wavefront, and the expected effect is small.",
   "verdict": "Only worth it if you accept that the trend may be tiny and build the report around testing that honestly. Choosing wavelength as the real variable, with density as the route to it, makes it far more defensible."
  },
  {
   "id": "single-slit-central-maximum-width-at-three-laser-wavelengths",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Single-slit central maximum width at three laser wavelengths",
   "researchQuestion": "How does the width of the central maximum of a single-slit pattern, 3.00 m from an adjustable slit, change as slit width is varied from 0.10 to 0.50 mm for a red laser?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Slit width, 0.10, 0.15, 0.20, 0.30, 0.40 and 0.50 mm (6 values), set with an adjustable slit or a set of printed slits and checked with a microscope. Repeat with green and red lasers at one slit width.",
   "dependentVariable": "Width of the central maximum measured with a metre rule or photograph with a scale, between the first minima on each side. Calculated angular half-width from width and screen distance.",
   "controlledVariables": "Screen distance: fixed at 3.00 m with a tape. Laser: same laser for the slit-width run. Alignment: beam through the slit centre, at right angles to the screen. Room lighting: dimmed to see the minima clearly.",
   "physicsNeeded": "For a single slit, the first minimum is at sinθ = λ/a, so the central maximum width w = 2λD/a. Plot w (y) against 1/a (x); gradient = 2λD, giving λ. For the wavelength part, plot w against λ at fixed a.",
   "slVsHl": "SL students verify the relation and compare λ with the stated laser value. Top band work checks the small-angle approximation, compares intensity profile with a light sensor, and treats a hair or wire as a complementary object.",
   "whereMarksAreLost": "Research design: only 2 or 3 wavelengths and slit widths, with no repeats. Data analysis: measuring the bright edge by eye where the intensity fades. Evaluation: not commenting on slit width accuracy.",
   "dataNote": "Needs lasers, adjustable slits and a long screen distance; the main uncertainty is where the minima sit and the true slit width.",
   "verdict": "A safe choice but a crowded one. Use the slit width as the main IV rather than colour, and measure the slit with a microscope to make it your own."
  },
  {
   "id": "single-slit-sound-intensity-pattern-from-a-loudspeaker",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Single-slit sound intensity pattern from a loudspeaker",
   "researchQuestion": "How does the sound intensity change with angle from the centre line, from 0° to 60° in 5° steps, behind a single slit of width 8.0 cm at a frequency of 3.0 kHz?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Detector angle θ from the central axis (0° to 60°, 13 values), set on a protractor arc around the slit; the speaker angle is fixed at 0°, and a second run turns the slit to change the angle of incidence.",
   "dependentVariable": "Sound level from a phone app or sound meter (dB) at fixed radius 1.0 m, converted to relative intensity I/I₀ = 10^(ΔL/10); the angle of the first minimum is found for each run.",
   "controlledVariables": "Frequency: signal generator set to 3.0 kHz and checked with a phone app. Slit width: two absorbing boards (foam or thick wood) fixed at 8.0 cm. Distance to the detector: a string of fixed length. Room: same room, the reflections reduced with soft material on nearby walls.",
   "physicsNeeded": "For a single slit, the first minimum is at a sin θ = λ, with λ = v/f. Plot sin θ of the minimum (y) against λ (x) for several frequencies, or against 1/a for several slit widths: the gradient is 1 (for a set of λ/a values). Also plot I/I₀ against θ and compare it with the sinc² profile.",
   "slVsHl": "SL: mapping intensity against angle and finding the first minimum, then checking a sin θ = λ. Top band: vary the width or frequency for a linear test, and model the pattern with the sinc² curve. Angle of incidence is a small extra since it just shifts the pattern.",
   "whereMarksAreLost": "Research design: reflections in a normal classroom ruin the pattern, and this is not controlled. Data analysis: not converting dB to intensity before comparing with the model. Conclusion: a claim that the pattern is right with no quantitative test. Evaluation: not addressing room echoes and the finite size of the microphone and phone response.",
   "dataNote": "Needs a signal generator, a speaker, and a calibrated sound meter or app; room reflections and the phone's frequency response are the main problems.",
   "verdict": "Interesting, but hard to get clean data indoors. It works better outdoors or with ultrasound transducers at 40 kHz where λ is small. Take it if you like a challenge and can show good control of reflections."
  },
  {
   "id": "sugar-concentration-and-rotation-of-polarised-light",
   "topic": "C.3",
   "topicName": "Wave phenomena",
   "level": "both",
   "title": "Sugar concentration and rotation of polarised light",
   "researchQuestion": "How does the concentration of a sucrose solution (0 to 500 g per litre in steps of 100 g/L) affect the angle through which the plane of polarised light is rotated over a 20 cm tube?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Sucrose concentration from 0 to 500 g/L, in 6 values, each prepared by mass and volume and repeated 3 times for the angle reading. Golden syrup diluted with water is a cheaper option.",
   "dependentVariable": "Rotation angle found by turning a second polariser to a minimum in transmitted light, using a protractor scale, or a light sensor with Malus's law for greater precision. Specific rotation is then calculated.",
   "controlledVariables": "Path length fixed by using the same tube; wavelength fixed with a single colour LED or laser; temperature kept constant at room temperature; solutions fully dissolved and free of bubbles.",
   "physicsNeeded": "Rotation θ = [α]·L·c, so θ is proportional to concentration. Plot θ against c; the gradient over L gives the specific rotation [α], with sucrose about 66.5° dm⁻¹ (g/mL)⁻¹ at 589 nm. Malus's law I = I0 cos²θ helps locate the minimum precisely.",
   "slVsHl": "An SL student can plot angle against concentration and compare the gradient with the literature. Top band work uses a light sensor and Malus's law to fit the position of the minimum, and studies the wavelength dependence.",
   "whereMarksAreLost": "Research design: judging the minimum by eye gives a large uncertainty. Data analysis: uncertainty in concentration ignored. Evaluation: unsealed tube, bubbles and scattering from undissolved sugar.",
   "dataNote": "Needs two polarising sheets, a clear tube, a monochromatic source and a scale; the main uncertainty is locating the intensity minimum by eye.",
   "verdict": "Simple and physical, with a literature value to compare against. Use a light sensor and fit Malus's law, or the eyeball uncertainty will dominate."
  },
  {
   "id": "resonance-lengths-in-a-closed-tube-and-the-end-correction",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Resonance lengths in a closed tube and the end correction",
   "researchQuestion": "How does the first resonant length of a closed tube depend on the frequency of a speaker between 400 Hz and 1200 Hz, and what end correction does the data give?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 4,
   "independentVariable": "Speaker frequency from 400 Hz to 1200 Hz in 100 Hz steps, giving 9 values, each with three repeats of the resonant length.",
   "dependentVariable": "Resonant length found by sliding the water level in a tall measuring cylinder or pipe, with a metre rule. Calculate 1/f and compare with 4(L + e)/v.",
   "controlledVariables": "Same tube diameter. Same speaker at constant output level held at the tube mouth at a fixed distance. Room temperature recorded at the start and end of each session. Same person judging the loudest point, or a phone microphone showing amplitude on a trace.",
   "physicsNeeded": "For a closed pipe the first resonance has L + e = λ/4 = v/4f, with e about 0.6 r. Plot L against 1/f. The gradient is v/4 and the negative intercept is the end correction e.",
   "slVsHl": "SL can find v and check it against v = 331 + 0.6θ. A higher band comes from using the intercept for e and testing e = 0.6 r with tubes of two diameters, and using higher harmonics. HL depth is possible through discussing boundary conditions and damping of the resonance.",
   "whereMarksAreLost": "Research design: overused topic so a trivial version reads as copied, and no plan for how the resonance peak is decided. Data analysis: plotting L against f and forcing the line through the origin, which throws away the end correction. Evaluation: not commenting on temperature change and the broad resonance peak.",
   "dataNote": "Needs a tone generator with a speaker, a tall cylinder with water and a rule; main uncertainty is locating the loudest position by ear, so use a microphone app.",
   "verdict": "Widely done, so it only earns credit if you do something extra. Focus on the end correction with two tube radii, or use it to find the speed of sound in a different gas like carbon dioxide released above the water."
  },
  {
   "id": "guitar-string-tension-against-fundamental-frequency",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Guitar string tension against fundamental frequency",
   "researchQuestion": "How does the tension in a 0.65 m steel guitar string, varied from 20 N to 60 N in 5 values, affect its fundamental frequency measured with a microphone and spectrum software?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 3,
   "independentVariable": "Tension in 8 to 10 values from 20 to 60 N, set by hanging masses over a pulley or by a spring balance, each measured 3 times.",
   "dependentVariable": "Fundamental frequency from a microphone and frequency analysis software such as Audacity, with a tuner app as a check. The measured mass per unit length is found from a mass and length measurement of a spare piece.",
   "controlledVariables": "Vibrating length fixed with bridges and measured with a ruler. Same string, so material and diameter are unchanged. Plucking position and strength kept alike. Room temperature stable, since the string changes length.",
   "physicsNeeded": "f = (1/2L)√(T/μ). Plot f² against T; the gradient is 1/(4L²μ), so μ can be found and compared with the value from weighing the string. A plot of f against √T also works.",
   "slVsHl": "SL students get the f² against T line and a value of μ. To reach the top band, compare μ from the gradient with the direct measurement, check the harmonic content, and consider stiffness and end effects. HL adds nothing specific but fits the treatment of standing waves.",
   "whereMarksAreLost": "Research design: tension changing as the string stretches or a poorly known T. Data analysis: linearising without uncertainty bars. Conclusion: not comparing gradient with the measured μ. Evaluation: ignoring the damping and pluck effects on the frequency.",
   "dataNote": "Needs a string setup, masses, a pulley and a microphone with software; tension calibration and frequency resolution are the main uncertainty.",
   "verdict": "Common (listed on 3 sites) but sound. The best personal twist is using an instrument you play and checking μ independently; a weak version just repeats f against T."
  },
  {
   "id": "damping-and-q-factor-of-a-driven-oscillator",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "HL",
   "title": "Damping and Q factor of a driven oscillator",
   "researchQuestion": "How does the added damping (card vanes of 0, 25 and 50 cm²) change the resonant frequency and quality factor of a driven mass on a spring?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Driving frequency, 0.5 to 2.0 Hz in steps of about 0.1 Hz (15 values) around resonance, at three damping levels set by vane area of 0, 25 and 50 cm².",
   "dependentVariable": "Steady-state amplitude of the mass, from video with a ruler behind or a motion sensor. Q = f₀/Δf found from the full width of the curve at 1/√2 of the peak amplitude.",
   "controlledVariables": "Driver amplitude (same throw of the vibration generator or motor crank); mass and spring (unchanged); time allowed at each frequency for transients to die (at least 20 s); vane shape and orientation.",
   "physicsNeeded": "Resonance curve of amplitude against frequency; peak frequency drops slightly with damping, and Q = f₀/Δf. Plot amplitude against driving frequency for each damping level and compare widths and heights.",
   "slVsHl": "Resonance and damping curves at this depth suit HL. An SL student could plot the curves and describe them qualitatively. Top band: model the curves with a driven damped oscillator equation and fit b.",
   "whereMarksAreLost": "Research design: driver amplitude changing with frequency and steady state not reached. Data analysis: too few points near the peak to find the width. Evaluation: not commenting on how the peak shifts.",
   "dataNote": "Needs a variable-frequency driver (function generator with vibration generator) and an amplitude measurement; the main uncertainty is transients and non-constant drive.",
   "verdict": "Ambitious and rewarding, but hard to get clean data. Choose it only if a stable driver is available, and take many points near resonance."
  },
  {
   "id": "end-correction-of-open-pipes-of-different-radius",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "End correction of open pipes of different radius",
   "researchQuestion": "How does the internal radius of an open pipe (from 1.0 to 3.5 cm, six pipes) affect its end correction, found from the resonant frequencies of a 40 cm pipe?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Internal radius of six open tubes of equal length 40.0 cm: about 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 cm, measured with vernier callipers.",
   "dependentVariable": "First three resonant frequencies, found with a loudspeaker and function generator and a microphone (oscilloscope or app). End correction e found from the fit of f against n/(2(L+2e)).",
   "controlledVariables": "Physical length of tube (cut to the same length, measured with a ruler); air temperature (recorded, taken as constant); loudspeaker position and distance (fixed); sound level from the generator.",
   "physicsNeeded": "For an open pipe, f_n = nv/(2(L + 2e)). Plot f against n for each tube: gradient v/(2(L+2e)) gives e if v is known. Then plot e against r, expecting e ≈ 0.6r.",
   "slVsHl": "SL can find e from the harmonics and compare with 0.6r. For a top-band result, treat speed of sound as a fitted value with uncertainty and handle its correlation with e.",
   "whereMarksAreLost": "Research design: pipes of differing length or wall material. Data analysis: assuming v with no temperature check. Evaluation: not commenting on how loudspeaker placement shifts resonances.",
   "dataNote": "PVC or cardboard tubes, a loudspeaker and a microphone with frequency-analysis software; the main uncertainty is picking the resonant peak.",
   "verdict": "A good choice for someone who likes wave work. The analysis is neat because two unknowns share one fit, so plan the fit before collecting."
  },
  {
   "id": "fundamental-frequency-of-a-vibrating-string-against-its-length",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Fundamental frequency of a vibrating string against its length",
   "researchQuestion": "How does the fundamental resonant frequency of a nylon string under a fixed 20 N tension vary with vibrating length from 0.30 m to 0.80 m in 0.10 m steps?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Vibrating length set by a movable bridge: 0.30, 0.40, 0.50, 0.60, 0.70, 0.80 m, each measured three times.",
   "dependentVariable": "Resonance frequency found by sweeping a signal generator connected to a vibrator (Hz) and judging maximum amplitude; wavelength taken as twice the length, and wave speed v = fλ calculated.",
   "controlledVariables": "Tension: fixed with a hanging mass over a pulley, checked each run. String: same piece, same linear density measured with a balance and metre rule. Vibrator amplitude: constant generator setting. Temperature: room conditions.",
   "physicsNeeded": "f = (1/2L)√(T/μ). Plot f against 1/L: gradient is half the wave speed, and √(T/μ) predicts it. Wave speed calculated at each length should be constant.",
   "slVsHl": "SL: f against 1/L and comparison of the speed with the value from T and μ. Top band: repeat by changing tension too, examine higher harmonics, and discuss end effects and the finding resonance peak width as the main uncertainty.",
   "whereMarksAreLost": "Research design: measuring frequency and wavelength as two independent outcomes when one follows from the other. Data analysis: judging resonance by eye without a repeat spread. Conclusion: no comparison with predicted speed. Evaluation: ignoring the vibrator not being a true node.",
   "dataNote": "Needs a signal generator, mechanical vibrator, pulley and masses; the main uncertainty is locating the exact resonant peak.",
   "verdict": "A good clean topic with a firm theory to test. Personalise it with a real instrument string such as a guitar or violin string and compare with its tuned note."
  },
  {
   "id": "pitch-drift-of-a-wire-as-its-temperature-changes",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Pitch drift of a wire as its temperature changes",
   "researchQuestion": "How does the fundamental frequency of a steel wire held between fixed supports change as its temperature is raised from 20 °C to 70 °C in steps of 10 °C?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Wire temperature, 20 to 70 °C in 6 values, set by passing a small controlled current or by a warm air stream, with each value repeated three times.",
   "dependentVariable": "Fundamental frequency from a phone spectrum analyser or a signal generator matched to resonance with a small driver coil, and wire temperature from a thermocouple taped to the wire.",
   "controlledVariables": "Wire length fixed by rigid clamps. Starting tension set with the same hanging mass. Same wire and same plucking or driving position. Ambient air movement kept low with a screen.",
   "physicsNeeded": "f = (1/2L)√(T/μ). Heating changes tension because the wire expands against fixed ends or hangs under a load, so plot f² against temperature. For a rigid frame, tension drops as the wire lengthens, so the gradient relates to the thermal expansion coefficient and Young's modulus.",
   "slVsHl": "SL students describe the frequency shift and link it to tension change. Top band work predicts the gradient from the expansion coefficient and Young's modulus and compares it with the measured one. The frame's own expansion should be evaluated.",
   "whereMarksAreLost": "Research design: no way to measure wire temperature reliably. Data analysis: tiny frequency changes hidden by resolution. Conclusion: explaining the result without a quantitative model. Evaluation: not commenting on uneven heating or the frame expanding.",
   "dataNote": "Needs a thermocouple and a spectrum app with fine resolution; the main uncertainty is that the frequency shift is small, and heating must not damage the wire.",
   "verdict": "Physically interesting but hard to get clean data. Take it only if you can control tension precisely, and use a metal wire rather than a nylon string."
  },
  {
   "id": "resonance-lengths-of-a-closed-air-column-and-the-end-correction",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Resonance lengths of a closed air column and the end correction",
   "researchQuestion": "How does the first resonant length L of an air column closed at one end, made with a tuning fork or a speaker tone, vary with driving frequency f from 256 Hz to 1024 Hz in 6 steps, and what end correction does this give for a tube of 30 mm internal diameter?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Driving frequency from a signal generator and speaker: 256, 320, 384, 512, 768 and 1024 Hz (6 values). Each resonant length found 5 times by sliding the water level up and down.",
   "dependentVariable": "Resonant length L of the air column (tube in a tall measuring cylinder of water, metre rule, ±1 mm). Calculate 1/f and the speed of sound from the gradient.",
   "controlledVariables": "Tube diameter, kept by using one tube throughout. Air temperature, read on a thermometer at the start and end. Speaker amplitude, held at one generator setting and one distance from the tube mouth. Same listener or a phone decibel app to judge the loudest point.",
   "physicsNeeded": "For a closed pipe, L + e = λ/4 = v/(4f), with e ≈ 0.6r. Plot L against 1/f. The gradient is v/4 and the intercept is minus e. Compare v with 331 + 0.6T.",
   "slVsHl": "SL students get v and e from the straight line and compare with the accepted value. Stronger work also finds the second resonance (3λ/4) to remove e without assuming it, tests e against tube radius using two tubes, and treats the fuzzy resonance peak as a proper uncertainty.",
   "whereMarksAreLost": "Research design: judging resonance by ear with no way of reducing bias. Data analysis: ignoring end correction, so the line does not pass through the origin. Evaluation: not explaining the effect of temperature drift or the broad resonance peak.",
   "dataNote": "Needs a signal generator, speaker, tall cylinder and tube; the main uncertainty is locating the loudest point, about ±5 mm.",
   "verdict": "A solid, cheap choice, but common in some form. Making the end correction the actual target, and testing it with two tube diameters, makes it yours."
  },
  {
   "id": "resonant-frequency-of-a-water-filled-glass-at-different-temperatures",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Resonant frequency of a water-filled glass at different temperatures",
   "researchQuestion": "How does the water temperature (10 to 80 degrees Celsius, 8 values) in a wine glass affect the fundamental frequency of the ring produced when it is tapped?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Water temperature from 10 to 80 degrees Celsius, about 8 values, set with ice and a kettle and read with a digital thermometer. Three taps at each value.",
   "dependentVariable": "Frequency from a phone spectrum app or a microphone with Audacity, taken as the peak of the FFT. Also record the temperature right after the taps.",
   "controlledVariables": "Water volume fixed at a marked level with a measuring cylinder; same glass and same tapping point and tool; microphone distance kept at 10 cm; room noise kept low.",
   "physicsNeeded": "Glass rim modes depend on the glass stiffness, mass and the liquid loading it. Water density changes very slightly with temperature. Plot f against temperature and check for a linear or null trend; discuss glass expansion and modulus.",
   "slVsHl": "SL students plot f against temperature and describe the trend with uncertainties. Top band work considers cooling during the run, the added mass of the liquid and whether the change is bigger than the frequency resolution.",
   "whereMarksAreLost": "Research design: the water cools during measurement, so the true temperature is unknown. Data analysis: frequency resolution of the app is coarser than the change. Conclusion: a physical explanation is asserted without evidence.",
   "dataNote": "Needs a glass, thermometer and a spectrum app; the main uncertainty is FFT resolution, so use a long recording window.",
   "verdict": "Fun and cheap, but the effect may be almost nothing. Make it personal by using your own glass, and state in advance that a null result is acceptable if the resolution is good enough to show it."
  },
  {
   "id": "resonant-frequency-of-an-lc-circuit-as-coil-turns-change",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "HL",
   "title": "Resonant frequency of an LC circuit as coil turns change",
   "researchQuestion": "How does the number of turns N on an air cored solenoid, from 20 to 120 in steps of 20, affect the resonant frequency of a parallel LC circuit with a fixed 100 nF capacitor?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Number of turns on the coil, 6 values from 20 to 120, built on the same former and each tested 3 times.",
   "dependentVariable": "Resonant frequency found by sweeping a signal generator and locating the peak amplitude on an oscilloscope (frequency error about ±1% of reading). Inductance is then calculated from f.",
   "controlledVariables": "Capacitance, using one measured capacitor. Coil length and diameter, kept fixed by winding on one former (turns spaced evenly along the same length). Drive amplitude, held constant on the generator. Core material, air only.",
   "physicsNeeded": "f = 1/(2π√(LC)) and for a long solenoid L ∝ N², so f ∝ 1/N. Plot 1/f against N, which should be a straight line through the origin. The gradient gives 2π√(C·μ₀A/l).",
   "slVsHl": "Because the LC oscillation and inductance sit in HL topics of induction, this fits HL best. An SL student could attempt it by treating it as a resonance study but would need to self teach inductance. Top band work checks the L ∝ N² prediction against a measured L from an LCR meter and considers coil resistance.",
   "whereMarksAreLost": "Research design: coil with too few turns gives frequencies too high to measure, and the stray capacitance is not considered. Data analysis: not linearising the relationship. Conclusion: overclaiming agreement with L ∝ N² for a short coil. Evaluation: leaving out the coil resistance and probe capacitance.",
   "dataNote": "Needs a signal generator, an oscilloscope, coil formers and enamelled wire. The main uncertainty is stray capacitance and finding the peak.",
   "verdict": "Good for HL students with an oscilloscope. It gives a clear prediction to test. Twist: insert an iron rod partly into the coil and find how f changes with insertion depth."
  },
  {
   "id": "ringing-pitch-of-a-stemmed-glass-versus-liquid-fill-level",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Ringing pitch of a stemmed glass versus liquid fill level",
   "researchQuestion": "How does the depth of tap water, varied from 0 to 80 mm in steps of 10 mm, in a thin-walled stemmed glass change the frequency of its fundamental ringing tone, measured with a microphone and spectrum software?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Height of water in one glass, 0, 10, 20, 30, 40, 50, 60, 70 and 80 mm (9 values), set with a syringe and checked against a ruler taped outside. Each level is struck 5 times.",
   "dependentVariable": "Fundamental frequency in Hz, taken from the strongest peak in a Fourier spectrum (Audacity or Phyphox) recorded by a phone or USB microphone. Mean and spread of the 5 strikes per level; percentage change from the empty glass is calculated.",
   "controlledVariables": "Same glass throughout, so wall thickness and shape do not vary. Same strike: a small rubber-tipped rod released from a fixed height, at the same spot on the rim. Water temperature kept at room value, checked with a thermometer. Microphone held at a fixed 10 cm distance, and the glass held on a foam pad to avoid damping differences.",
   "physicsNeeded": "The rim vibrates in a standing-wave mode, and water adds mass that moves with the wall, lowering the frequency. Treat it as a mass-spring system, f = (1/2π)√(k/m_eff), where m_eff = m_glass + a·m_water. Plot 1/f² against water mass (from volume and density): the line should be straight, with the gradient giving a/(4π²k)... in short, gradient = 4π²·a/k and the intercept relates to the empty glass. Note that the added water mass only approximately fits at low levels, so check where the straight line fails.",
   "slVsHl": "SL: collect the frequencies, plot f against depth, describe the fall and give a sensible uncertainty. Better SL work linearises 1/f² against water mass and comments on the fit. HL depth: build the effective mass model with a fitted coefficient a, test whether the intercept matches the mass of the glass part that vibrates, compare the fundamental with the second mode, or model how the added fluid loading changes with depth. Also justify why the residuals show a trend.",
   "whereMarksAreLost": "Research design: choosing the water volume but not the glass geometry, so the relation is not comparable across glass shapes, or not explaining how the microphone position and the strike are held constant. Data analysis: reading the pitch by ear or a tuner app without uncertainty, and ignoring the FFT frequency resolution (set by the recording length). Conclusion: claiming a simple 'more water means lower frequency' without testing any model, or forcing a straight line through a curved trend. Evaluation: not spotting that water-glass coupling is not a simple added mass at low levels, that the glass may crack or the rim may not be the only vibrating part, and that strike-to-strike variation is not the only error.",
   "dataNote": "Needs a thin glass, a microphone or phone with a spectrum app and a syringe; the main uncertainty is the FFT resolution and the small change in pitch at low water levels.",
   "verdict": "A cheap, sound-based investigation that works well if you actually test a model rather than only describing the trend. Twist: repeat with two glass shapes or add a second mode so the conclusion is not just 'higher volume, lower pitch'. Because several sites list the basic version, use a modelling angle to stand out."
  },
  {
   "id": "ringing-time-of-a-plucked-string-against-vibrating-length",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Ringing time of a plucked string against vibrating length",
   "researchQuestion": "How does the vibrating length of a guitar string, from 0.25 m to 0.65 m in steps of 0.05 m, affect the time taken for its sound level to fall to half its initial amplitude?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Vibrating length set by a movable bridge on a monochord or guitar, 0.25 to 0.65 m in 9 values, with 3 plucks each.",
   "dependentVariable": "Decay of sound amplitude recorded by a phone microphone at a fixed position using a free audio app; half-life of the envelope read off the waveform. Frequency also read from the spectrum.",
   "controlledVariables": "Tension fixed by tuning the open string to the same frequency check before each set, or by a hanging mass. Plucking displacement fixed with a jig. Microphone distance and room the same. Same string.",
   "physicsNeeded": "Envelope A = A0 e^(-t/τ), so plot ln A against t and take the gradient for the damping constant. Then plot τ against length. Link to f = (1/2L)√(T/μ) to explain why frequency changes with L at fixed tension.",
   "slVsHl": "SL students extract a decay time for each length and describe the trend. Top band work separates the frequency effect from the length effect, for example by plotting the number of oscillations before decay. HL depth can add a damping model.",
   "whereMarksAreLost": "Research design: pluck force not truly constant, and frequency changing along with length. Data analysis: reading the decay by ear or by a stopwatch. Conclusion: overclaiming a cause when frequency and length change together. Evaluation: ignoring the sound produced by the body of the instrument.",
   "dataNote": "Needs a monochord and a phone or sound sensor; the main uncertainty is a repeatable pluck.",
   "verdict": "Fun and personal if you play, but the frequency confound is serious. Use a monochord and analyse in cycles as well as seconds."
  },
  {
   "id": "second-harmonic-frequency-of-a-stretched-string-against-tension",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Second harmonic frequency of a stretched string against tension",
   "researchQuestion": "How does the tension in a 0.80 m nylon or steel string (from 10 N to 60 N in 6 steps) affect the frequency of its second harmonic?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Tension from hanging masses of 1.0 to 6.0 kg over a pulley (6 values). Five repeated frequency finds per tension.",
   "dependentVariable": "Frequency at which a vibration generator drives a clear two loop standing wave, read on the signal generator, or measured with a phone spectrum app from a plucked string. Best judged by maximum amplitude.",
   "controlledVariables": "Vibrating length: fixed between bridge and pulley, measured with a metre rule. String: same string throughout, with its linear mass density μ found by weighing a measured length. Drive amplitude: kept low and constant. Temperature: room conditions, no heating of the string.",
   "physicsNeeded": "f = (n/2L)√(T/μ), so for n = 2, f = (1/L)√(T/μ). Plot f² against T; a straight line through the origin has gradient 1/(L²μ), which can be checked against the measured μ.",
   "slVsHl": "SL: get the straight line and compare the gradient with the calculated value. Top band: propagate uncertainty in μ and L, test other harmonics to confirm the n dependence, and discuss end effects and string stiffness.",
   "whereMarksAreLost": "Research design: masses not calibrated and the pulley friction ignored. Data analysis: plotting f against T and forcing a curve. Conclusion: no comparison of gradient with theory. Evaluation: finding resonance by ear with a wide uncertainty.",
   "dataNote": "Needs a vibration generator, signal generator, pulley and masses; the main uncertainty is picking the resonance peak and pulley friction.",
   "verdict": "Solid and reliable, but very commonly done in some form. Make it yours by using a real instrument string such as a guitar string and comparing with the tuning note."
  },
  {
   "id": "speed-of-sound-in-air-helium-and-carbon-dioxide",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Speed of sound in air, helium and carbon dioxide",
   "researchQuestion": "How does the molar mass of a gas (air, helium, carbon dioxide, and mixtures of helium and air in 0 to 100% steps) affect the speed of sound found from resonance in a closed tube at 20 °C?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Gas composition, five to six values: air, CO2, helium, and two or three helium and air mixtures, made in a balloon or bag and filled into the tube.",
   "dependentVariable": "Resonant frequency of a 0.50 m tube found with a tone generator and a phone microphone or oscilloscope, three repeats. Speed of sound calculated from v = 4Lf for the fundamental.",
   "controlledVariables": "Tube length, measured with a rule and end correction included. Temperature, monitored with a thermometer at each run. Tube flushed with at least three volumes of gas. Same volume amplitude from the speaker.",
   "physicsNeeded": "v = fλ and, for a closed tube, λ = 4(L + 0.6r). Kinetic theory gives v = √(γRT/M), so plot v² against 1/M, where the gradient is about γRT.",
   "slVsHl": "SL students compare measured speeds with the values expected from the equation. Top work considers how γ differs between monatomic and diatomic gases and the mixing fraction to get M.",
   "whereMarksAreLost": "Research design: 'acoustic properties' is too vague, so focus on speed only. Data analysis: gas contamination changes M. Evaluation: not correcting for temperature or the end effect.",
   "dataNote": "Helium and CO2 need to be available safely from a school supplier; leakage and air mixing at the open end are the main uncertainty.",
   "verdict": "Original and interesting because it links waves and gas theory. Use only safe gas quantities with the teacher's approval, and note that the gas cannot be pure."
  },
  {
   "id": "speed-of-sound-in-gases-from-resonance-in-a-tube",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Speed of sound in gases from resonance in a tube",
   "researchQuestion": "How does the speed of sound in a closed tube filled with air, carbon dioxide and helium mixtures compare when found from resonance frequencies between 200 and 1500 Hz?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Gas composition, such as air, air with 25%, 50% helium, and carbon dioxide; at least 4 gases or mixtures. Sweep the frequency in 10 Hz steps and repeat 3 times.",
   "dependentVariable": "Resonant frequencies found with a signal generator, speaker and microphone on an oscilloscope, or a phone app for the amplitude; speed calculated from the tube length and the harmonics.",
   "controlledVariables": "Same tube length, checked with a metre rule; temperature measured with a thermometer for each gas; speaker and microphone at fixed positions; the tube sealed at one end with a stopper or a foil sheet.",
   "physicsNeeded": "For a tube closed at one end, f_n = n v/(4L) with odd n, and v = √(γRT/M). Plot resonant frequency against harmonic number; the gradient gives v/(2L). Compare v with the predicted value from the molar mass.",
   "slVsHl": "SL: the speed from the gradient for each gas and comparing with the accepted values. Top band or HL: derive v from γ and M, apply an end correction of 0.6r, and determine γ for the mixture.",
   "whereMarksAreLost": "Research design: changing gas without safety planning or a way to fill the tube and keep the concentration. Data analysis: ignoring the end correction. Evaluation: gas leaking or mixing with air, which changes the composition.",
   "dataNote": "Needs a signal generator, a tube, a microphone and safely handled gases; the main uncertainty is gas purity and leaks.",
   "verdict": "Good but hard to keep clean. A safer version is to vary the tube length with air only, or to use small helium balloons under supervision, and to check the temperature dependence instead."
  },
  {
   "id": "speed-of-sound-in-humid-air-using-a-resonance-tube",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Speed of sound in humid air using a resonance tube",
   "researchQuestion": "How does the relative humidity of air, from about 40% to 95%, affect the speed of sound in a resonance tube, at a fixed temperature near 25 °C?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Relative humidity of air in the tube: five to six values between roughly 40% and 95%, set by allowing damp air to enter, or using a humidifier, and read with a hygrometer, with 3 repeats each.",
   "dependentVariable": "Resonant lengths found for a tuning fork of fixed frequency using a tube with a moving water level or plunger. Speed v = 4f(L + 0.3d) for a closed tube, or from the gradient of successive resonance lengths. Humidity and temperature are logged at each run.",
   "controlledVariables": "Temperature, held within 0.5 °C using a thermometer inside the tube. Same tuning fork frequency, checked against a phone app. Same tube diameter and length. Same method of finding the resonance point, using the loudest sound.",
   "physicsNeeded": "Humid air is less dense than dry air, so the speed of sound increases slightly with water vapour content. The full change from 40% to 95% is only about 0.3 to 0.5%, so v against humidity is very nearly flat and the uncertainty matters more than the trend. Plot v against humidity or against the vapour fraction.",
   "slVsHl": "SL: measure v for the humidities and state whether a change is seen within the uncertainty. Top band: predict the size of the effect from the molar mass of moist air and compare it with the resolution of the method. HL depth: use the ideal gas relation for speed in a mixture.",
   "whereMarksAreLost": "Research design: the effect is smaller than the uncertainty of the method and temperature changes swamp it. Data analysis: no uncertainty propagation. Conclusion: claiming a trend that lies within the error. Evaluation: not recognising that the design could not detect the expected effect.",
   "dataNote": "Needs a resonance tube, tuning forks, a hygrometer and a thermometer; the effect is under 0.5%, so precision and temperature control are hard.",
   "verdict": "Risky because the expected change is smaller than most school setups can resolve. Only choose it if you plan the precision first, and correct for temperature using v = 331 + 0.6T. A careful null result is still acceptable."
  },
  {
   "id": "speed-of-sound-through-rods-of-different-materials-by-resonance",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Speed of sound through rods of different materials by resonance",
   "researchQuestion": "How does the speed of longitudinal waves in solid rods of about 1 m length differ between aluminium, copper, steel, brass and glass, and does it agree with v = √(E/ρ) using data-book values?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Rod material: 5 rods of similar length, with a repeat of the lengths for one material at 3 different lengths (0.5, 0.75, 1.0 m).",
   "dependentVariable": "Fundamental frequency of the rod held at its centre and tapped at one end, recorded with a phone spectrum app or microphone, 5 taps each. Calculate v = 2Lf and compare with √(E/ρ).",
   "controlledVariables": "Support position, at the exact midpoint by a foam clamp. Rod length, measured with a metre rule to ±1 mm. Tap strength and position. Temperature of the room.",
   "physicsNeeded": "A rod free at both ends has f = v/(2L) and v = √(E/ρ). Plot f against 1/L for one material to check the gradient equals v/2, then plot v measured against v predicted for all materials.",
   "slVsHl": "SL students compare measured v with the predicted one for each material. HL depth: link the Young modulus to the atomic bonding picture, and analyse the frequency spectrum overtones as odd and even harmonics.",
   "whereMarksAreLost": "Research design: the input idea of timing a delay over a short path is far too crude, so use resonance. Data analysis: not propagating the density and modulus uncertainty. Evaluation: ignoring rod alloy differences from book values.",
   "dataNote": "Needs rods, a foam clamp and a phone spectrum app; frequency resolution of the app sets uncertainty, about ±1 Hz.",
   "verdict": "I changed the original to be feasible, since timing sound over short paths in liquids does not work at school. This gives clear numbers and good comparison with theory."
  },
  {
   "id": "tension-and-wave-speed-on-a-stretched-string",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Tension and wave speed on a stretched string",
   "researchQuestion": "How does the tension in a nylon string (2 to 20 N, six values) affect the speed of transverse waves found from standing-wave resonances at a fixed string length of 1.00 m?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Tension from hanging masses of 0.2, 0.5, 1.0, 1.5, 2.0, 2.5 kg over a pulley (about 2 to 25 N), six values.",
   "dependentVariable": "Resonant frequency of the fundamental found by scanning a function generator connected to a vibration generator, with node positions checked. Wave speed v = 2Lf₁ (calculated).",
   "controlledVariables": "Vibrating length (fixed by two marked bridges at 1.00 m); string (same string, mass per unit length measured by weighing 2 m); driver amplitude (kept just large enough to see the loops); string temperature and stretch.",
   "physicsNeeded": "v = √(T/μ) and v = fλ. Plot v² against T: the gradient is 1/μ, which can be checked against the measured μ. Alternatively plot f against √T.",
   "slVsHl": "SL can do the full analysis using v² against T and compare μ. To reach top band, discuss the resonance width, stretching of the string with tension and compare higher harmonics.",
   "whereMarksAreLost": "Research design: string length not held constant when the string stretches. Data analysis: judging resonance by eye with no estimate of frequency uncertainty. Evaluation: ignoring pulley friction and the end effect at the vibrator.",
   "dataNote": "Vibration generator, signal generator, pulley and masses; the main uncertainty is finding the exact peak of resonance.",
   "verdict": "A classic, so it needs a twist such as comparing strings of different μ or testing harmonics. Well within reach and gives a clean linear graph."
  },
  {
   "id": "wave-speed-on-wires-of-different-materials",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Wave speed on wires of different materials",
   "researchQuestion": "How does the fundamental frequency of wires of equal diameter, 0.40 mm, and equal length, 0.60 m, depend on their density for five metals at a tension of 40 N?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Density of wire material, five metals such as steel, copper, brass, aluminium and nichrome, using tabulated densities and checked by weighing a measured length of each.",
   "dependentVariable": "Fundamental frequency from resonance driven by a signal generator and coil, or a microphone spectrum; density also checked by mass on a balance divided by volume.",
   "controlledVariables": "Length fixed on a sonometer. Tension set with hanging masses. Diameter checked with a micrometer for every wire. Room temperature noted.",
   "physicsNeeded": "f = (1/2L)√(T/μ), μ = ρA. Plot f² against 1/ρ, expecting a straight line with gradient T/(4L²A). Note magnetic wires respond differently to the driver coil, so a microphone or a mechanical driver is better.",
   "slVsHl": "SL students plot f² against 1/ρ and check the linear trend. Top band work uses measured densities, addresses the fact that only five values with limited spread are available, and quantifies the gradient uncertainty. Materials also differ in stiffness, which is a good evaluation point.",
   "whereMarksAreLost": "Research design: uncontrolled diameter between wires. Data analysis: using textbook densities without checking the wire's actual composition. Conclusion: ignoring that few materials limit the fit. Evaluation: not discussing that the wire is not perfectly flexible.",
   "dataNote": "Needs a sonometer and several wires of one gauge; the main uncertainty is the small number of materials and mismatched diameters.",
   "verdict": "Works but has fewer independent values than most IAs need, so measure each density yourself. A better twist is to vary diameter instead."
  },
  {
   "id": "wire-material-and-the-fundamental-frequency-of-a-string",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Wire material and the fundamental frequency of a string",
   "researchQuestion": "How does the linear mass density of strings of different materials (nylon, steel, cotton, copper, fishing line) affect the fundamental resonance frequency at 0.60 m length and 20 N tension?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Linear mass density μ of five to seven strings, found by weighing 1 m lengths, covering about 0.1 to 5 g/m.",
   "dependentVariable": "Fundamental frequency found by tuning a signal generator and vibration driver until the amplitude of the standing wave peaks, with the frequency read from the generator to 0.1 Hz, or from a phone spectrum app.",
   "controlledVariables": "Vibrating length fixed between two bridges, measured with a metre rule. Tension set by hanging a fixed mass over a pulley and checking it does not change. Same drive amplitude. Same temperature and same clamps.",
   "physicsNeeded": "f = (1/2L)√(T/μ). Plot f² against 1/μ or f against μ^(−1/2), gradient = √T/(2L). Material only enters through μ, which is the key conclusion.",
   "slVsHl": "SL students can show f ∝ μ^(−1/2) across the materials. Stronger work checks whether material affects f beyond μ, for example stiffness in steel. HL depth is not required, but higher harmonics add analysis.",
   "whereMarksAreLost": "Research design: 'material' cannot be controlled with a fixed diameter, since density and diameter both change μ. Data analysis: reading a broad resonance peak by ear. Evaluation: stretch of nylon changing tension.",
   "dataNote": "Needs a signal generator, vibration driver and a set of strings; the peak amplitude is broad, which limits frequency precision.",
   "verdict": "A good choice once you replace 'material' with linear density, because then the graph is clean and the physics is testable. Twist: use strings from your own guitar or cello."
  },
  {
   "id": "wire-thickness-and-pitch-on-a-sonometer",
   "topic": "C.4",
   "topicName": "Standing waves and resonance",
   "level": "both",
   "title": "Wire thickness and pitch on a sonometer",
   "researchQuestion": "How does the diameter of a steel wire, from 0.20 mm to 0.60 mm, affect its fundamental frequency at a fixed length of 0.60 m and tension of 50 N?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Wire diameter, 6 wires from 0.20 to 0.60 mm, each measured with a micrometer at 5 places along the wire.",
   "dependentVariable": "Fundamental frequency found by driving with a signal generator and a small coil until the wire resonates with maximum amplitude, or read from a microphone spectrum. Mass per unit length calculated from the diameter and density.",
   "controlledVariables": "Length fixed by the bridges on a sonometer. Tension set by the same hanging masses, checked on a newton meter. Same steel material, checked from the supplier. Same drive coil position.",
   "physicsNeeded": "f = (1/2L)√(T/μ) with μ = ρπd²/4, so f ∝ 1/d. Plot f against 1/d, expecting a straight line through the origin with gradient (1/2L)√(4T/(ρπ)).",
   "slVsHl": "SL students plot f against 1/d and compare with the predicted gradient. Top band work uses the gradient to extract the wire density or tension and compares it against a known value. HL students can extend to comparing transverse and longitudinal waves.",
   "whereMarksAreLost": "Research design: wires of different materials mixed in. Data analysis: micrometer variation along the wire ignored. Conclusion: no comparison of gradient to theory. Evaluation: not commenting on the wire stiffness and end effects at thick diameters.",
   "dataNote": "Needs a sonometer, a micrometer and a signal generator; the main uncertainty is the resonance width and the tension reading.",
   "verdict": "A clean, well controlled investigation with a strong theoretical link. It is popular in some form, so use the gradient to extract a material property."
  },
  {
   "id": "frequency-shift-from-a-buzzer-on-a-moving-trolley",
   "topic": "C.5",
   "topicName": "Doppler effect",
   "level": "both",
   "title": "Frequency shift from a buzzer on a moving trolley",
   "researchQuestion": "How does the speed of a 2000 Hz buzzer on a dynamics trolley, varied from 0.2 to 1.2 m/s in six steps, affect the frequency shift heard by a fixed microphone?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Trolley speed, 0.2 to 1.2 m/s in 0.2 m/s steps (6 values), 3 to 5 runs each. Speed set by a weighted string and pulley or a motorised trolley, and measured with two light gates.",
   "dependentVariable": "Frequency heard on approach, measured by recording the microphone signal in Audacity or Phyphox and reading the peak from an FFT. Shift is calculated as f_obs minus f_source, with f_source measured on the stationary buzzer.",
   "controlledVariables": "Buzzer frequency: check it with the trolley at rest before every run. Microphone position and height: clamp it 20 cm from the track. Room temperature: record it and use it for the speed of sound. Background noise: run in the same quiet room and keep the battery fresh.",
   "physicsNeeded": "f_obs = f_s · v / (v − u) for an approaching source. Plot Δf against u; the gradient is about f_s/v_sound, so the speed of sound can be extracted and compared with 343 m/s at the room temperature. Better, plot 1/f_obs against u, which is linear.",
   "slVsHl": "SL students test the linear relation and compare the gradient to the expected value. Top marks come from a proper uncertainty in the gradient and from handling the microphone geometry (approach angle), which is not quite head-on. HL students can add the receding branch and analyse the varying frequency during the pass.",
   "whereMarksAreLost": "Research design: speeds too low so the shift is lost in FFT resolution. Data analysis: reading frequency from a short clip with poor resolution and no uncertainty. Evaluation: ignoring the angle between motion and microphone and the buzzer's frequency drift as the battery fades.",
   "dataNote": "Needs a battery buzzer, trolley, track, two light gates and a microphone with FFT software; the main uncertainty is frequency resolution on a short recording, at about 1 to 2 Hz.",
   "verdict": "Worth choosing if you can get short, clean recordings. The shift at trolley speeds is only a few Hz, so make it personal by using a higher pitch or a rotating source and checking the resolution first."
  },
  {
   "id": "radial-velocities-of-stars-from-shifted-absorption-lines",
   "topic": "C.5",
   "topicName": "Doppler effect",
   "level": "both",
   "title": "Radial velocities of stars from shifted absorption lines",
   "researchQuestion": "What radial velocities, in km/s, follow from the shift of the H-alpha line (656.28 nm) in archive spectra of 10 to 15 stars, and how does the scatter compare with the catalogue values?",
   "dataDifficulty": 2,
   "dataSource": "database",
   "sitesListingIt": 1,
   "independentVariable": "Catalogue radial velocity of each star, 10 to 15 stars covering roughly -100 to +100 km/s, taken from one archive.",
   "dependentVariable": "Observed centre of the H-alpha line found by fitting a Gaussian in software, giving velocity from v = c(delta lambda/lambda0).",
   "controlledVariables": "Same spectral line for every star. Same archive and instrument resolution. Same line fitting method and fitting window. Spectra corrected to the same wavelength reference, either air or vacuum, for all stars.",
   "physicsNeeded": "Non-relativistic Doppler shift delta lambda/lambda0 = v/c. Plot calculated velocity against catalogue velocity, expecting gradient 1 and intercept 0; the residuals show the precision.",
   "slVsHl": "SL: measure shifts, compute velocities, compare with catalogue. Top band: use two or three lines to check consistency, and discuss the resolution limit of the spectrograph. HL: add relativistic correction and discuss when it matters.",
   "whereMarksAreLost": "Research design: air and vacuum wavelengths mixed. Data analysis: no uncertainty on the line centre. Conclusion: no statement of the gradient and its uncertainty. Evaluation: ignores Earth's orbital motion correction and instrument resolution.",
   "dataNote": "Needs archive spectra and a line fitting tool; the key uncertainty is the wavelength resolution, which may be comparable to the shift for slow stars.",
   "verdict": "A good data investigation if you are careful with the wavelength reference. Add a twist by including one binary star at several dates to see the velocity change."
  },
  {
   "id": "testing-kepler-s-third-law-with-moons-of-jupiter",
   "topic": "D.1",
   "topicName": "Gravitational fields",
   "level": "both",
   "title": "Testing Kepler's third law with moons of Jupiter",
   "researchQuestion": "Does the period squared against orbital radius cubed for the four Galilean moons follow a straight line, and what mass of Jupiter, in kg, results?",
   "dataDifficulty": 1,
   "dataSource": "database",
   "sitesListingIt": 1,
   "independentVariable": "Orbital radius cubed for 4 moons of Jupiter, or 6 to 8 bodies if more moons or another planet are added, from a public data table.",
   "dependentVariable": "Orbital period squared, taken from the table or measured from sequential telescope or simulator images; central mass calculated from the gradient as M = 4 pi^2/(G x gradient).",
   "controlledVariables": "Same central body for all satellites. Radii measured from the planet's centre, not surface. Same data source and units throughout. Near circular orbits chosen so the radius is well defined.",
   "physicsNeeded": "Newton's gravitation with circular motion gives T^2 = (4 pi^2/GM) r^3. Plot T^2 against r^3; gradient 4 pi^2/GM. A log-log plot tests whether the exponent is 3.",
   "slVsHl": "SL: linear graph and a mass of Jupiter compared with the accepted value. Top band: log-log fit for the exponent with its uncertainty, and a check for eccentricity effects. HL: discuss deviations from a point mass, such as planetary oblateness.",
   "whereMarksAreLost": "Research design: using only tabulated values with no reason or check on source. Data analysis: too few points, and no uncertainty. Conclusion: comparison with accepted mass without a percentage difference. Evaluation: only generic comments, no mention of eccentricity.",
   "dataNote": "Only a data table and spreadsheet needed; to be more original measure moon positions yourself from images, where pixel scale is the main uncertainty.",
   "verdict": "Safe and easy, but only fine if you add depth. Measuring positions from real images or a simulator gives you your own data and lifts it above a table lookup."
  },
  {
   "id": "weight-against-mass-and-local-g-from-a-force-sensor",
   "topic": "D.1",
   "topicName": "Gravitational fields",
   "level": "both",
   "title": "Weight against mass and local g from a force sensor",
   "researchQuestion": "How does the weight of brass slotted masses from 0.050 kg to 0.500 kg vary with mass, and what value of gravitational field strength g results from the gradient?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Mass hung from the sensor: 10 values from 0.050 to 0.500 kg, each measured 3 times, with the masses checked on an electronic balance.",
   "dependentVariable": "Force read from a digital force sensor (or a calibrated newton meter) in newtons; g is taken as the gradient of weight against mass.",
   "controlledVariables": "Location: same bench and height throughout. Sensor zero: reset with nothing hanging before each reading. Mass hanging still: readings taken once oscillation has stopped. Temperature and sensor orientation: kept vertical and unchanged.",
   "physicsNeeded": "W = mg in a uniform field. Plot W against m; the gradient is g, expected near 9.8 N per kg. Compare with the accepted local value and with g from a free-fall or pendulum measurement.",
   "slVsHl": "SL students find g with an uncertainty and compare it with 9.81. Extra depth: use a different method for g and see whether the two values agree within uncertainty, and estimate how g changes with altitude between floors of the school using a very sensitive sensor.",
   "whereMarksAreLost": "Research design: the question is trivial and lacks an unknown. Conclusion: stating a gradient without comparing with an accepted value. Evaluation: not addressing sensor calibration and zero error.",
   "dataNote": "A force sensor, slotted masses and a balance; the main uncertainty is the calibration and zero offset of the sensor.",
   "verdict": "As it stands it is too easy and might score poorly on depth. Only choose it if you turn it into a comparison of two methods for g, or a measurement of g at different heights."
  },
  {
   "id": "turns-on-an-electromagnet-and-its-pulling-force",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Turns on an electromagnet and its pulling force",
   "researchQuestion": "How does the number of turns (20 to 120 in steps of 20) on an iron-cored electromagnet at constant current of 1.0 A affect the magnetic field measured 1.0 cm from its end, in mT?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 3,
   "independentVariable": "Number of turns N: 20, 40, 60, 80, 100, 120, rewound on the same core, 3 repeats each.",
   "dependentVariable": "Field strength from a Hall probe or phone magnetometer at a fixed distance, in mT. Optional second measure: mass of paper clips or steel washers lifted.",
   "controlledVariables": "Current held at 1.0 A by adjusting a power supply and checked with an ammeter each run. Same core and coil diameter. Same probe distance, fixed by a clamp. Short readings only, to stop the wire heating and the resistance drifting.",
   "physicsNeeded": "For a solenoid B = μ₀nI, so B is proportional to N at fixed length. Plot B against N and compare the gradient with the prediction; with an iron core expect a larger effective permeability and eventual saturation.",
   "slVsHl": "SL students can plot B against N and test proportionality. Top band work compares the gradient with μ₀I/L, discusses the core's relative permeability and finds where the graph departs from linearity.",
   "whereMarksAreLost": "Research design: current falling as turns are added because resistance rises, and no control of it. Data analysis: ignoring that winding length also changes. Evaluation: overlooking Earth's field and background offset in the probe.",
   "dataNote": "Needs a Hall probe or a calibrated phone magnetometer; the main uncertainty is probe position and coil heating.",
   "verdict": "Overdone, listed on three sites, so choose it only if you handle the changing coil length and heating. Test the iron core against an air core for your own angle."
  },
  {
   "id": "capacitance-of-parallel-plates-with-different-dielectric-sheets",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Capacitance of parallel plates with different dielectric sheets",
   "researchQuestion": "How does the capacitance of a parallel plate capacitor with plates of 15 cm × 15 cm change when different sheets of thickness 1 mm to 5 mm of acrylic are placed between them?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Thickness of the dielectric between the plates, d from 1 mm to 5 mm using stacked acrylic sheets (5 values); a second run compares acrylic, glass, paper and cardboard sheets at the same thickness.",
   "dependentVariable": "Capacitance measured with a capacitance meter (pF) or by the discharge time constant τ = RC through a known resistor with a data logger; charge from Q = CV.",
   "controlledVariables": "Plate area: same two aluminium plates, measured with a rule. Plate separation: set by the sheet thickness measured with a micrometer, with plates pressed evenly. Voltage: a fixed 5.0 V for charge calculations. Humidity and stray capacitance: same wires and layout, zero reading with wires alone subtracted.",
   "physicsNeeded": "C = ε₀εᵣA/d. Plot C (y) against 1/d (x): the gradient is ε₀εᵣA, giving εᵣ. Stray capacitance from the meter leads gives a positive intercept. Q = CV then follows.",
   "slVsHl": "SL: a linear plot of C against 1/d and εᵣ from the gradient, compared with data. Top band: subtract the stray capacitance, deal with the air gaps between plates and sheets, and compare materials by εᵣ with uncertainty.",
   "whereMarksAreLost": "Research design: the original mixes materials and capacitance and charge without a clear plan, and does not say how C is measured. Data analysis: small pF values with a large stray contribution. Conclusion: the εᵣ found is not compared with accepted values. Evaluation: air gaps between the plates and sheets lower the apparent εᵣ, and this is missed.",
   "dataNote": "Needs two metal plates, sheets of insulator and a capacitance meter or logger; the main uncertainty is the air gap and stray capacitance.",
   "verdict": "A good choice, as it gives a real relationship and a natural linear graph, though it is a low-capacitance measurement so care is needed. The twist is comparing your εᵣ with tables and explaining any air gap effect."
  },
  {
   "id": "counting-excess-electrons-on-a-balloon-from-its-repulsion-of-a-second",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Counting excess electrons on a balloon from its repulsion of a second charge",
   "researchQuestion": "Using Coulomb's law, how many excess electrons are on a rubbed balloon, found from the deflection of a suspended second balloon at separations of 4 to 12 cm?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Separation r between two identically charged balloons, 4 to 12 cm in 1 cm steps (at least six values), each charged by the same rubbing routine and repeated three times.",
   "dependentVariable": "Deflection angle of a light balloon or foil ball hung on a thread, measured from a video frame with a ruler grid. Force from F = mg tan(theta), charge q from F = kq^2/r^2, and number of electrons N = q/e.",
   "controlledVariables": "Humidity monitored with a hygrometer and kept in a narrow range; identical mass and size of the two objects; same rubbing material and count of strokes; thread length constant.",
   "physicsNeeded": "Coulomb's law F = kq1q2/r^2 and force balance on a suspended charge. Plot F against 1/r^2, gradient = kq^2, so q = sqrt(gradient/k). Charge leaks with time so timing matters.",
   "slVsHl": "SL students get q and N and comment that the answer is of order 10^10 to 10^11. Top band work models charge leakage over time and separates the effect of induced charge on the neutral parts of the setup.",
   "whereMarksAreLost": "Data analysis: assuming point charges though balloons are large. Evaluation: charge decay during measurements and humidity ignored. Conclusion: no comparison with a known charge scale.",
   "dataNote": "Balloons, thread, camera and ruler are enough; charge leaks quickly and balloons are not point charges, so the uncertainty is large.",
   "verdict": "Fun and cheap but hard to make rigorous. Use small foil-coated spheres instead of balloons to make the point charge model defensible."
  },
  {
   "id": "elementary-charge-from-balanced-or-falling-oil-droplets",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Elementary charge from balanced or falling oil droplets",
   "researchQuestion": "What value of the elementary charge e is found from at least 15 oil droplets by measuring their rise and fall times in a Millikan apparatus at 300 to 500 V?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Droplet identity (charge on each droplet), at least 15 droplets, each timed over several rise and fall traverses; optionally two plate voltages such as 300 V and 500 V.",
   "dependentVariable": "Fall time and rise time across a fixed number of graticule divisions, using a stopwatch or video; charge on each droplet calculated, then the smallest common divisor of all charges found.",
   "controlledVariables": "Plate spacing fixed; oil density and temperature recorded; same graticule distance for each timing; plate voltage measured with a voltmeter and held constant during a traverse.",
   "physicsNeeded": "Terminal velocity from Stokes' law 6 pi eta r v = weight minus upthrust; then q = mg/E at balance or from the rise and fall speeds. Plot charge against droplet number, sorted, and look for steps; gradient of q against integer n gives e.",
   "slVsHl": "SL students calculate q and find approximate multiples of e. Top band work applies the Cunningham slip correction, uses a statistical test for the divisor, and evaluates the effect of droplet evaporation.",
   "whereMarksAreLost": "Data analysis: small droplets and Brownian motion cause scatter, and students force the result to 1.6 times 10^-19 C. Evaluation: reaction time in stopwatch timing not treated.",
   "dataNote": "Needs a Millikan apparatus, which many schools lack; timing droplets by eye is hard and reaction time is the main uncertainty.",
   "verdict": "Only worth choosing with real apparatus, and then it is strong. If you do not have the kit, a database or simulation study is much weaker, so consider another topic."
  },
  {
   "id": "equipotential-mapping-between-different-electrode-shapes",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Equipotential mapping between different electrode shapes",
   "researchQuestion": "How does the electric field strength, in V m⁻¹, vary with distance from the centre of a circular electrode in conducting paper, compared with a parallel plate arrangement, over 1 cm to 8 cm?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Position along a radial line, 8 values at 1 cm spacing, for two electrode geometries (parallel plates and a central disc with an outer ring).",
   "dependentVariable": "Potential measured with a digital voltmeter and probe on conducting paper (uncertainty ±0.01 V). Calculated: E = −ΔV/Δx between neighbouring points.",
   "controlledVariables": "Supply voltage: fixed at 10 V and checked. Paper: same sheet or same batch, to keep resistivity constant. Electrode contact: silver conductive paint for a uniform edge. Probe pressure: light and consistent.",
   "physicsNeeded": "E = −dV/dx. For a parallel plate E is constant; for a point-like or radial arrangement E ∝ 1/r. Plot V against ln r (gradient related to charge factor) or E against 1/r and check for linearity.",
   "slVsHl": "SL students can map potential and estimate E from slopes. A top band study tests the 1/r prediction with a linearised graph and quantifies the deviation near the edges. HL depth can come from relating the results to potential and field theory for radial fields.",
   "whereMarksAreLost": "Research design: too few points near the electrode where the field changes fastest. Data analysis: computing E from widely spaced points without considering the error this brings. Evaluation: ignoring paper non-uniformity and edge effects.",
   "dataNote": "Needs conducting paper, a low voltage DC supply and a digital voltmeter; the main uncertainty is inhomogeneous paper and probe contact.",
   "verdict": "Simple to run and easy to get right, but examiners want quantitative analysis, not just a picture. Add a linearised graph for the radial case and it becomes worthwhile."
  },
  {
   "id": "field-inside-a-solenoid-against-current-to-find-mu-zero",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Field inside a solenoid against current, to find mu-zero",
   "researchQuestion": "How does the current I in a solenoid (0.5 to 3.0 A, six values) affect the flux density at its centre, and what value of the permeability of free space follows?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Solenoid current from 0.5 to 3.0 A in steps of 0.5 A, using a variable DC supply and ammeter, with three readings for each current and the direction reversed once.",
   "dependentVariable": "Flux density B at the centre from a calibrated Hall probe, in mT; mu0 calculated from the gradient of B against I with the known number of turns per metre.",
   "controlledVariables": "Number of turns and solenoid length measured once; probe kept on the axis and centre, held by a clamp; probe zeroed with current off each time; coil not left on long to avoid heating.",
   "physicsNeeded": "For a long solenoid B = mu0 n I. Plot B against I: gradient = mu0 n, so mu0 = gradient/n. Length to diameter ratio should be at least 10 for the formula to hold, otherwise an end correction is needed.",
   "slVsHl": "SL students get mu0 with a percentage difference from the accepted value. Top band work adds an iron core to find relative permeability, or maps B along the axis and compares with theory.",
   "whereMarksAreLost": "Data analysis: the probe zero offset and Earth's field give a non-zero intercept and are ignored. Evaluation: coil heating raises resistance and lowers current. Note the RQ should say permeability of free space, not relative permeability.",
   "dataNote": "Solenoid, DC supply, ammeter and Hall probe; probe calibration and background field are the main uncertainty.",
   "verdict": "Solid and safe but common in spirit. Make it yours by adding an iron core or by comparing solenoid length against diameter and testing when the long solenoid formula breaks down."
  },
  {
   "id": "field-strength-at-different-distances-from-a-straight-wire",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Field strength at different distances from a straight wire",
   "researchQuestion": "How does the magnetic flux density B change with perpendicular distance r, from 1 cm to 8 cm in 1 cm steps, from a long straight wire carrying 5.0 A?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Perpendicular distance r from the wire, 1 to 8 cm (8 values), measured to the sensor's element with a ruler and repeated 3 times.",
   "dependentVariable": "Flux density measured with a Hall probe or a phone magnetometer, corrected by subtracting the reading with the current off. Field is reported in microtesla.",
   "controlledVariables": "Current: hold at 5.0 A with a power supply, checked with an ammeter. Wire orientation: keep it vertical and straight, away from steel. Probe orientation: keep the sensitive axis tangential to the field. Earth's field and the surroundings: take a zero reading each time and use the same location.",
   "physicsNeeded": "B = μ₀I/(2πr). Plot B against 1/r; gradient is μ₀I/2π, so μ₀ = 2π·gradient/I, compared with 4π × 10⁻⁷ N A⁻². At 5 A and 5 cm, B is only about 20 µT, comparable to Earth's field.",
   "slVsHl": "SL students plot B against 1/r and compare μ₀ with the accepted value. Top band adds the uncertainty on r from the sensor's unknown internal position, treated as an offset in the intercept. HL can add the vector sum with the Earth's field.",
   "whereMarksAreLost": "Research design: current too small so the signal is buried in noise. Data analysis: forgetting to subtract the background. Evaluation: not considering the finite wire length and the sensor's position inside its casing, and wire heating.",
   "dataNote": "Needs a Hall probe or magnetometer and a supply giving 5 to 10 A; a loop of wire and heating may limit the current, and the uncertainty from probe position is dominant.",
   "verdict": "Worthwhile and hands-on. Use a fit of B = k/(r + r₀) so that the unknown sensor offset becomes a result of your own, which makes it more than a routine test."
  },
  {
   "id": "field-uniformity-between-two-coils-at-varying-spacing",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Field uniformity between two coils at varying spacing",
   "researchQuestion": "How does the separation of two identical coils, varied from 0.5R to 1.5R in six steps, affect the percentage variation of the on-axis field over the central 4 cm?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Coil separation d, 6 values from 0.5R to 1.5R where R is the coil radius (for example 5 cm to 15 cm for R = 10 cm), with the field mapped at 9 or more positions for each.",
   "dependentVariable": "On-axis field measured with a Hall probe along a ruler; uniformity is calculated as (B_max − B_min)/B_centre × 100% across the central 4 cm.",
   "controlledVariables": "Coil current: hold constant with a DC supply and check with an ammeter. Coil alignment: keep the axes collinear with a common rod. Probe orientation: keep it along the axis. Background field: subtract the current-off reading.",
   "physicsNeeded": "For a Helmholtz pair, B = (4/5)^(3/2) μ₀NI/R at the centre when d = R, and the second derivative of B along the axis is zero there. Plot uniformity (%) against d/R and find the minimum; compare with d = R.",
   "slVsHl": "SL students plot uniformity against separation and identify the best spacing. Top band compares the centre field to the theory value and considers the effect of coil thickness. HL can derive the on-axis field formula and show why the second derivative vanishes at d = R.",
   "whereMarksAreLost": "Research design: too few axial positions so that uniformity is not resolved. Data analysis: not using a percentage measure consistently. Evaluation: ignoring the finite thickness of the coils and the probe's position error.",
   "dataNote": "Needs two matching coils, a 1 to 2 A supply and a Hall probe; the position uncertainty of about 1 mm and probe noise limit the uniformity to about 1%.",
   "verdict": "An excellent choice with a clear theory target at d = R. Do it as one focused study of coil separation and leave out the solenoid turn-density variant."
  },
  {
   "id": "levitation-height-of-a-magnet-above-a-fixed-base-magnet",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Levitation height of a magnet above a fixed base magnet",
   "researchQuestion": "How does the mass of a floating ring magnet (adding 5 g to 40 g of weights in steps of 5 g) affect its equilibrium height above a fixed magnet on a plastic rod?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Added mass on the floating ring magnet from 5 g to 40 g in 5 g steps, eight values, three trials each.",
   "dependentVariable": "Gap between the magnets, measured from a photo taken with a ruler in frame, in mm; the field of the base magnet is measured separately with a Hall probe against distance.",
   "controlledVariables": "Same pair of magnets; alignment on a smooth vertical plastic rod; same time allowed for settling; no steel or magnetic objects nearby.",
   "physicsNeeded": "At equilibrium repulsion equals weight, F = mg. For dipoles F falls roughly as 1/h^4, so plot ln(m) against ln(h) with gradient about -4. The stronger the magnet, the higher it floats for a given load.",
   "slVsHl": "SL students give the power law and its exponent. Top band work compares different magnet grades and models the finite size of the magnets rather than point dipoles.",
   "whereMarksAreLost": "Research design: field strength cannot be varied directly, so vary mass instead and measure field separately. Data analysis: friction against the rod adds hysteresis. Evaluation: photo parallax.",
   "dataNote": "Ring magnets, a plastic rod, small masses and a camera; friction on the rod and parallax in the photo cause most of the scatter.",
   "verdict": "Simple and doable, and good for a power law graph. Change the IV to mass and keep magnet field for a secondary measurement, so the RQ is actually testable."
  },
  {
   "id": "magnetic-flux-density-of-a-neodymium-magnet-from-0-to-80-degrees-celsi",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Magnetic flux density of a neodymium magnet from 0 to 80 degrees Celsius",
   "researchQuestion": "How does the flux density measured 5 mm from the pole of a ferrite magnet change as its temperature is raised from 20 to 90 degrees Celsius in eight steps?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Magnet temperature, eight values from 20 to 90 degrees Celsius, set in a water bath and checked by thermometer; three repeat readings per value, with a cooling run to check reversibility.",
   "dependentVariable": "Flux density B from a Hall probe or a phone magnetometer (calibrated) held at a fixed 5 mm distance by a 3D printed or wooden jig, in mT.",
   "controlledVariables": "Probe to magnet distance fixed by the jig; probe zeroed for background field before every reading; same orientation of the magnet; measurement made quickly after removal from bath while noting the cooling.",
   "physicsNeeded": "Ferromagnetic order weakens as thermal energy rises towards the Curie temperature. Over a small range B is close to linear with T, so plot B against T with gradient in mT per degree. Ferrite decreases more slowly than neodymium and strongly hysteretic behaviour may show.",
   "slVsHl": "SL students report the gradient and compare with the supplier's temperature coefficient. Top band work checks reversibility, and separates reversible and irreversible loss.",
   "whereMarksAreLost": "Research design: the magnet cools between bath and probe and the temperature is wrong; probe sensitivity itself changes with temperature. Evaluation: heating too high causes permanent loss.",
   "dataNote": "Needs a Hall probe or calibrated magnetometer and a heated water bath; probe temperature drift and cooling during measurement are the main uncertainties.",
   "verdict": "Original and personal. Do it with a thin waterproof coat on the magnet and a probe kept away from the heat, or your data will show the probe rather than the magnet."
  },
  {
   "id": "magnetic-response-of-metals-from-force-on-a-balance",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Magnetic response of metals from force on a balance",
   "researchQuestion": "How does the apparent change in mass of iron, aluminium and copper samples of equal volume depend on the current through an electromagnet, from 0.5 A to 4.0 A in steps of 0.5 A?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Electromagnet current (0.5 A to 4.0 A, 8 values) at a fixed distance, with three materials as a second variable.",
   "dependentVariable": "Change in reading of a top pan balance (0.01 g) with the sample hung above the pole; the force is F = Δm g, and the field is measured with a Hall probe (mT).",
   "controlledVariables": "Sample volume and shape: cylinders of the same size, checked with calipers. Distance from the pole: fixed with a spacer. Temperature: coil allowed to cool between readings to avoid changing current. Position: sample held in place with a non-magnetic thread.",
   "physicsNeeded": "Force on a sample in a non-uniform field is proportional to χVB(dB/dx)/μ₀, so F is proportional to B² for a constant gradient. Plot F (y) against B² (x): the gradient gives χ. Iron is ferromagnetic and not linear, and copper is diamagnetic, so it is repelled. A true hysteresis loop needs a B and H measurement on the way up and down.",
   "slVsHl": "SL: qualitative and quantitative comparison of the three materials and a plot of F against B². Top band: run the current up and then down for iron to show hysteresis, and estimate χ for aluminium. HL is not required, but the analysis is demanding.",
   "whereMarksAreLost": "Research design: the input idea asks for susceptibility and hysteresis together, which is too much for one IA. Data analysis: forces for copper and aluminium are tiny and comparable to balance noise, so the uncertainty is not treated. Conclusion: claiming a value of χ with no comparison to the tables. Evaluation: not commenting on the field gradient and remnant magnetism in the core.",
   "dataNote": "Needs an electromagnet, a sensitive balance and a Hall probe; the forces on copper and aluminium are near the noise level.",
   "verdict": "Too ambitious as written, and I would narrow it to iron only, with hysteresis by running the current up and down. It is a real novelty and unusual, but keep the scope small."
  },
  {
   "id": "mapping-field-uniformity-between-plates-with-a-conducting-paper-probe",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Mapping field uniformity between plates with a conducting paper probe",
   "researchQuestion": "How does the plate separation d (1.0 to 6.0 cm, six values) affect the width of the region where the electric field is uniform to within 5 percent between two parallel plates at fixed voltage?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Plate separation d from 1.0 to 6.0 cm in 1.0 cm steps, set with spacers, at least six values, three traverses each.",
   "dependentVariable": "Width of the central region where the potential gradient stays within 5 percent of the mid value, found by moving a voltmeter probe across conducting paper or a shallow water tray and taking potential at 0.5 cm intervals.",
   "controlledVariables": "Supply voltage fixed at about 10 V DC (or low AC with an AC probe in water); plate length and width fixed; same paper or same water depth and conductivity; probe moved along the same centre line.",
   "physicsNeeded": "For ideal plates E = V/d. Edge fringing grows with d. Plot uniform width against d; ratio of uniform width to plate length against d/L is a good dimensionless graph. Equipotential lines are perpendicular to field lines.",
   "slVsHl": "SL students map potentials and find the trend. Top band work compares with a simulation (for example a free field solver) and explains fringing quantitatively.",
   "whereMarksAreLost": "Research design: 'area of uniform field' is not measurable until a 5 percent criterion is defined. Data analysis: probe positions with no uncertainty. Evaluation: paper resistivity not uniform.",
   "dataNote": "Conducting paper kit, power supply and a digital voltmeter; the main uncertainty is probe contact and paper inhomogeneity.",
   "verdict": "A good fit if you define the uniformity threshold clearly. Add your own comparison with a numerical solver to make it yours."
  },
  {
   "id": "motor-speed-against-core-material-in-a-hand-wound-electromagnet",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Motor speed against core material in a hand-wound electromagnet",
   "researchQuestion": "How does the magnetic flux density at the end of a 200-turn electromagnet vary with core material (air, iron nail, steel bolt, copper rod, aluminium rod, ferrite) when a current of 0.50 A is used?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Core material: 6 types of the same 100 mm length and diameter. A second run varies current from 0.2 to 1.0 A in 5 steps for the best core.",
   "dependentVariable": "Magnetic flux density B measured with a Hall probe (or phone magnetometer) at a fixed 10 mm from the core end, 3 readings each. Calculate the relative permeability from B against the air core value.",
   "controlledVariables": "Number of turns and coil geometry, one coil used for all cores. Current, held by a variable power supply and checked on an ammeter. Probe position, fixed by a clamp and ruler. Coil temperature, kept low by short switching on periods.",
   "physicsNeeded": "Solenoid field B = μ0 μr nI. Plot B against I for the iron core. The gradient is μ0 μr n, so μr can be found. Compare across materials.",
   "slVsHl": "SL students compare the cores and one current series. To reach the top: explain saturation and remanence, correct for Earth's field, and show B against I bending over.",
   "whereMarksAreLost": "Research design: the original motor version has too many uncontrolled variables, so I moved to the electromagnet. Data analysis: not subtracting background field. Evaluation: heating changing coil resistance and current.",
   "dataNote": "Needs a Hall probe or phone magnetometer and a power supply; the main uncertainty is probe position, as B falls quickly with distance.",
   "verdict": "I turned a vague motor efficiency idea into a clean field measurement. The saturation curve is the personal twist, and it makes the physics deeper."
  },
  {
   "id": "photodiode-current-against-distance-from-a-lamp",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Photodiode current against distance from a lamp",
   "researchQuestion": "How does the distance from a small LED lamp to a photodiode, varied from 10 cm to 60 cm in steps of 10 cm, affect the short circuit photocurrent, and does it follow an inverse square law?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Distance x from lamp to photodiode along a metre rule, 6 to 8 values from 10 to 60 cm, each repeated 3 times.",
   "dependentVariable": "Photocurrent measured with a multimeter on the microamp range, or the voltage across a fixed resistor from a data logger.",
   "controlledVariables": "Lamp power: stabilised supply with a fixed current and warm up time. Ambient light: dark room or a black tube, with a background reading subtracted. Alignment: lamp and diode on the same axis, diode facing the lamp. Temperature of the diode: short readings so it stays constant.",
   "physicsNeeded": "For a point source, intensity I = P/(4πx²), and the photocurrent is proportional to intensity within the linear range. Plot I_photo against 1/x². Straight line through the origin means the law holds. A log-log plot gives the exponent. Curved data at short range shows the source is not a point.",
   "slVsHl": "SL students confirm the trend with a linear graph. Top band work subtracts background, tests that current is linear in intensity with filters, and includes an effective origin correction for the lamp filament position. HL students can connect to photon flux and the photoelectric effect.",
   "whereMarksAreLost": "Research design: stray light not controlled or subtracted. Data analysis: distance measured to the wrong reference point. Conclusion: forcing an inverse square fit at short distances where it fails. Evaluation: not checking saturation of the photodiode.",
   "dataNote": "Only a lamp, a photodiode, a multimeter and a ruler are needed, and the main uncertainty is stray light and the offset of the true source position.",
   "verdict": "Safe and easy but it can look basic. Add a twist by fitting the offset in x, or by comparing an LED with a filament lamp to see how the pattern changes."
  },
  {
   "id": "testing-the-inverse-square-law-with-charged-spheres",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Testing the inverse square law with charged spheres",
   "researchQuestion": "How does the separation between two charged metal-coated polystyrene spheres, varied from 2.0 cm to 10.0 cm in steps of 2.0 cm, affect the electrostatic force between them, found from the deflection angle of a hanging sphere?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Centre to centre separation r of two charged spheres, 5 to 6 values from 2.0 to 10.0 cm, each repeated 3 to 5 times.",
   "dependentVariable": "Deflection angle of a suspended sphere, read from a photo against a protractor or by trigonometry on a ruler. Force is calculated as F = mg tanθ.",
   "controlledVariables": "Charge on each sphere: recharge from the same supply for a fixed time and check with a field meter or note the voltage. Sphere mass and thread length: same pair throughout. Humidity: run in one session, note it, use a dry room. Height of the spheres: aligned with a levelled stand.",
   "physicsNeeded": "Coulomb's law F = kq1q2/r². Plot F against 1/r², a straight line through the origin if the law holds. Gradient is kq1q2, and if the charge is roughly known the value of k can be compared with the accepted one. Charge leakage means the exponent is worth fitting with a log-log plot too.",
   "slVsHl": "SL students verify the trend and the linear plot. Top band work fits the exponent with uncertainty, corrects for the fact that the force is not horizontal at large angles, and models charge leakage over time. HL students can link to field strength and potential.",
   "whereMarksAreLost": "Research design: charge not kept constant, so the variable is uncontrolled. Data analysis: uncertainty in r ignored, and no treatment of the angle error. Conclusion: claiming exactly r⁻² without a fitted exponent and its error. Evaluation: not discussing charge leakage and induced charges in nearby objects.",
   "dataNote": "Needs a high voltage supply or a charged rod, and humidity ruins repeatability, so the main uncertainty is charge decay between readings.",
   "verdict": "Physically classic but hard to get clean data in a normal school room. Worth it only if you can control humidity and measure charge, otherwise choose something more forgiving. A personal twist is to test how fast the charge leaks and correct for it."
  },
  {
   "id": "where-a-bar-magnet-starts-to-behave-like-a-dipole",
   "topic": "D.2",
   "topicName": "Electric and magnetic fields",
   "level": "both",
   "title": "Where a bar magnet starts to behave like a dipole",
   "researchQuestion": "How does the on-axis field B of a cylindrical neodymium magnet fall with distance x from 2 cm to 20 cm, and at what distance does the exponent reach 3?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Axial distance x from the magnet centre, 2 to 20 cm in 2 cm steps (10 values), 3 repeats.",
   "dependentVariable": "Field strength measured with a Hall probe or a phone magnetometer along a ruler, with the zero-magnet reading subtracted. The exponent is found from the gradient of ln B against ln x for different ranges of x.",
   "controlledVariables": "Magnet orientation: keep the axis aligned along the ruler. Sensor orientation: keep the sensitive axis on the magnet axis. Nearby iron and electronics: clear the bench and use a wooden ruler. Background field: measure it before each run and subtract.",
   "physicsNeeded": "For a dipole, B = μ₀m/(2πx³) on the axis, so B ∝ x⁻³ at large x. Plot ln B against ln x; gradient tends to −3 as x becomes larger than the magnet size. Compare gradients from near and far subsets.",
   "slVsHl": "SL students fit a power law and quote the exponent with its uncertainty. To reach the top band, separate the near-field and far-field fits and explain the change with the magnet length. HL can estimate the magnetic moment m and use a finite-magnet model.",
   "whereMarksAreLost": "Research design: readings too close where the sensor saturates. Data analysis: measuring from the wrong reference point on the magnet. Evaluation: not correcting for background, and taking centre versus end distance.",
   "dataNote": "Needs a strong magnet and a Hall probe or magnetometer; the position of the sensing element inside the phone is unknown and adds to the uncertainty of x.",
   "verdict": "A good option for a student who enjoys graphs. The twist is treating the exponent as a function of distance rather than assuming −3 from the start."
  },
  {
   "id": "electron-mass-from-a-deflection-tube-using-electric-and-magnetic-field",
   "topic": "D.3",
   "topicName": "Motion in electromagnetic fields",
   "level": "both",
   "title": "Electron mass from a deflection tube using electric and magnetic fields",
   "researchQuestion": "What value of the electron mass is obtained from a deflection tube when the accelerating voltage is varied from 2000 to 5000 V (six values) and the magnetic deflection radius is measured?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Accelerating voltage V from 2000 to 5000 V in 500 V steps, with Helmholtz coil current adjusted or held fixed, three readings each.",
   "dependentVariable": "Radius r of the electron beam path read from the tube scale, coil current measured with an ammeter to get B, then e/m calculated. The electron mass follows only by using the accepted value of e.",
   "controlledVariables": "Helmholtz coil current for each set kept constant with a stable supply; tube orientation aligned so that the field is perpendicular to the beam; Earth's field cancelled or its direction noted; warm up time kept the same.",
   "physicsNeeded": "eV = 1/2 mv^2 and evB = mv^2/r give e/m = 2V/(B^2 r^2). Plot r^2 against V at fixed B: gradient = 2m/(eB^2). B from a Helmholtz coil: B = (4/5)^1.5 mu0 N I / R. Then m = e/(e/m).",
   "slVsHl": "SL students get e/m and m from one linear graph. Top band work quantifies B uncertainty, corrects for Earth's field and discusses parallax on the beam radius.",
   "whereMarksAreLost": "Research design: mass cannot be measured directly, so the RQ should be e/m and then mass with a quoted e. Evaluation: parallax on radius and uniformity of B missed.",
   "dataNote": "Needs a school fine beam tube with Helmholtz coils and an EHT supply; parallax on the beam radius is the main error.",
   "verdict": "Good and classic if your school owns the tube. Frame it as e/m first, then mass, and be open that e is taken from the literature."
  },
  {
   "id": "magnetic-force-on-a-wire-versus-current",
   "topic": "D.3",
   "topicName": "Motion in electromagnetic fields",
   "level": "both",
   "title": "Magnetic force on a wire versus current",
   "researchQuestion": "How does the current in a 5.0 cm straight wire, varied from 1.0 A to 5.0 A in steps of 0.5 A, change the force it feels between two magnadur magnets, measured in mN?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Current through the wire, 1.0 to 5.0 A in 9 steps (at least 5 values), each repeated 3 times, with the wire held perpendicular to the field.",
   "dependentVariable": "Force on the wire, found from the change in reading on a top-pan balance (0.001 g resolution) that supports the magnet yoke; F = Δm g. Calculated: F/L for each current.",
   "controlledVariables": "Active length of wire: fixed by using the same pole width, checked with a ruler. Angle to the field: set by clamping the wire and checking with a protractor. Field strength: same magnet pair, same position, checked with a Hall probe. Heating: current switched on only for a few seconds per reading.",
   "physicsNeeded": "F = BIL sin θ. Plot F (y) against I (x): a straight line through the origin with gradient BL, so B = gradient / L. Compare B with a Hall probe reading.",
   "slVsHl": "SL students can get a clean linear graph and a value of B with uncertainty. Top band work checks the Hall probe value, discusses the fringe field beyond the poles, and tests whether the effective length is really the pole width. HL depth can come from repeating with the angle varied and fitting sin θ.",
   "whereMarksAreLost": "Research design: not controlling the effective length or the balance drift. Data analysis: ignoring the zero offset and uncertainty in the small mass changes. Evaluation: not commenting on fringe fields and wire heating.",
   "dataNote": "Needs a top-pan balance, a variable DC supply, an ammeter and magnadur magnets; the main uncertainty is the small force (a few mN) and the non-uniform field at the pole edges.",
   "verdict": "A solid, classic set-up that works in a school lab. Make it yours by comparing the balance-derived B with a Hall probe, or by testing how the field falls off near the magnet edges."
  },
  {
   "id": "neodymium-magnet-stack-size-and-simple-motor-rotation-rate",
   "topic": "D.3",
   "topicName": "Motion in electromagnetic fields",
   "level": "both",
   "title": "Neodymium magnet stack size and simple motor rotation rate",
   "researchQuestion": "How does the number of stacked neodymium magnets (1 to 6, each 10 mm diameter) under a battery-and-wire homopolar or coil motor affect its rotation rate, in revolutions per second?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Number of identical stacked magnets, 1 to 6, giving six values; each value repeated 5 times. Field strength at the coil is measured separately with a Hall probe.",
   "dependentVariable": "Rotation rate from slow-motion phone video (240 fps) counting frames per revolution, in rev/s; Hall probe reading of B in mT at the coil position.",
   "controlledVariables": "Same battery, checked with a voltmeter before each run; same coil or wire shape and mass; same contact resistance, cleaned and rewound each run; same distance from magnet to coil, set with a spacer.",
   "physicsNeeded": "Force on a current-carrying conductor F = BIL, so torque and speed rise with B until friction and back emf balance. Plot rotation rate against B measured by the Hall probe. Check whether the line is straight and what the intercept says about friction.",
   "slVsHl": "SL: measure rate against B and describe the trend with uncertainties. Top band: model back emf and friction to explain why rate levels off. HL can link to induced emf in D.4.",
   "whereMarksAreLost": "Research design: field strength is assumed from magnet count instead of measured. Data analysis: rate is timed by eye with large uncertainty. Evaluation: battery voltage drift and contact friction ignored.",
   "dataNote": "Needs a Hall probe, magnets and a phone camera; the main uncertainty is inconsistent electrical contact and battery drain between runs.",
   "verdict": "Worth doing if you measure B directly rather than just counting magnets. Adding a fixed load and comparing torque is a good personal twist."
  },
  {
   "id": "number-of-coil-turns-and-speed-of-a-simple-dc-motor",
   "topic": "D.3",
   "topicName": "Motion in electromagnetic fields",
   "level": "both",
   "title": "Number of coil turns and speed of a simple DC motor",
   "researchQuestion": "How does the number of turns on the coil of a simple DC motor (10 to 60 turns, 6 values) affect its no load rotation rate at a fixed supply voltage of 3.0 V?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Number of turns of enamelled copper wire on the rotor coil, 10, 20, 30, 40, 50, 60 turns, rewound each time on the same former. Three repeats per value.",
   "dependentVariable": "Rotation rate measured from video in slow motion at 240 fps by counting frames per revolution, or with a phone strobe app, in revolutions per second. Angular velocity ω = 2π f. Current from an ammeter recorded alongside.",
   "controlledVariables": "Supply voltage: fixed at 3.0 V from a bench supply and checked with a voltmeter under load. Magnet strength and gap: same magnets, same position. Coil size and wire gauge: same former and same wire. Friction at the bearings: same supports, same lubrication, coil balanced by eye.",
   "physicsNeeded": "Torque on a coil τ = NBIA sin θ, and back emf ε = NBAω sin θ. With more turns the resistance also rises, so the current falls. At steady speed the supply voltage balances back emf and resistive drop, so ω is roughly V/(NBA) if resistance is small, meaning speed may fall with N, not rise. Plot ω against 1/N and see if the result is linear.",
   "slVsHl": "SL: measure and describe the trend, and explain using force on a current in a field. Top band or HL: use back emf and Faraday's law to predict the shape, and link the torque and resistance to the fitted curve, from D.4 induction (HL).",
   "whereMarksAreLost": "Research design: unbalanced hand made coils give erratic speeds and this is not controlled. Data analysis: speed not converted to a proper unit and no uncertainty. Conclusion: a prediction of faster speed with more turns not tested against the physics. Evaluation: unreliable starts, wire heating and contact friction at the commutator.",
   "dataNote": "Needs a simple motor kit, magnets, enamelled wire and slow motion video; the main uncertainty is friction and contact resistance at the brushes.",
   "verdict": "Only worth it if you can build a repeatable motor, and expect surprises, since more turns may not mean faster. Twist: measure current as well and show how back emf explains the trend."
  },
  {
   "id": "magnet-drop-speed-and-peak-coil-voltage",
   "topic": "D.4",
   "topicName": "Induction",
   "level": "HL",
   "title": "Magnet drop speed and peak coil voltage",
   "researchQuestion": "How does the release height of a magnet (0.05 to 0.50 m, 6 heights) affect the peak induced EMF in a 500-turn coil, and does the area under the EMF-time pulse stay constant?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "Release height above the coil, 0.05 to 0.50 m in 6 steps, each repeated 5 times. Speed at the coil is found from v = √(2gh) or from light gate timing.",
   "dependentVariable": "Peak EMF read from a voltage sensor and data logger (at least 1 kHz sampling). Area under each pulse is found by numerical integration to give the change in flux linkage.",
   "controlledVariables": "Same magnet and coil, so N and magnet strength are fixed. Same tube guiding the fall, so the path is centred. Same logger resistance and sampling rate. Magnet orientation kept the same every drop.",
   "physicsNeeded": "Faraday's law, ε = −N dΦ/dt. Plot peak EMF against v (expect roughly linear) and integrated EMF against v (expect flat, equal to NΔΦ). The flat line is the real test of the law.",
   "slVsHl": "Induction is HL content, so this is an HL idea. Peak EMF against speed alone is a modest piece of work. Adding the integration, comparing it with a calculated NΔΦ from a measured magnet field, and explaining the asymmetric pulse (magnet accelerating) takes it to the top band.",
   "whereMarksAreLost": "Research design: assuming free fall speed when eddy current braking and tube friction exist. Data analysis: reading peak by eye from a low sampling rate and ignoring uncertainty in v. Evaluation: not addressing why the second pulse peak is larger than the first.",
   "dataNote": "Needs a coil, neodymium magnet and a fast data logger; the main uncertainty is the true speed at the coil and the sampling rate clipping peaks.",
   "verdict": "Very common (overdone), so it only works with the integration and speed check. The twist is measuring your own magnet's field to predict the area under the curve."
  },
  {
   "id": "coil-diameter-and-acceleration-of-a-coil-in-a-magnet-track",
   "topic": "D.4",
   "topicName": "Induction",
   "level": "HL",
   "title": "Coil diameter and acceleration of a coil in a magnet track",
   "researchQuestion": "How does the diameter of a copper coil (10 to 25 mm, five sizes) of fixed turns affect its acceleration along a track of neodymium magnets on a battery-powered coil train?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Coil diameter, 10 to 25 mm in five or six steps, made by winding the same length of enamelled wire on different formers; 5 repeats each.",
   "dependentVariable": "Acceleration from video analysis in Tracker, using a metre rule in frame, in m/s²; resistance of each coil from a multimeter.",
   "controlledVariables": "Number of turns and wire gauge; battery type and charge state; magnet spacing on the track; mass of the train, adjusted with plasticine.",
   "physicsNeeded": "Force on the current-carrying coil F = nBIL in the magnet field, with L the circumference. Larger diameter means more wire length in the field but higher resistance. Plot acceleration against coil circumference, with mass corrected.",
   "slVsHl": "Mostly HL, as induction and back emf are D.4. An SL student could treat it as force on a conductor (D.3) and stay at description. Top band models current with resistance and back emf.",
   "whereMarksAreLost": "Research design: mass and resistance change with diameter and are not controlled. Data analysis: acceleration from noisy position data. Evaluation: unreliable battery contacts.",
   "dataNote": "Needs Tracker, strong magnets and wire; the main uncertainty is friction and irregular coil contact with the magnets.",
   "verdict": "Fun but messy. Only choose it if you measure current and resistance too, so that the explanation has real numbers."
  },
  {
   "id": "coupled-coils-and-how-induced-voltage-falls-with-separation",
   "topic": "D.4",
   "topicName": "Induction",
   "level": "HL",
   "title": "Coupled coils and how induced voltage falls with separation",
   "researchQuestion": "How does the axial separation x (x = 2 to 20 cm in 2 cm steps) between two coaxial coils affect the peak voltage induced in a 200 turn pickup coil driven by a 1.0 kHz, 2.0 V signal?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Separation x between the coil faces, 2, 4, 6, 8, 10, 12, 16, 20 cm, measured on a metre rule, three readings each.",
   "dependentVariable": "Peak to peak voltage in the pickup coil read from an oscilloscope, halved to give the amplitude.",
   "controlledVariables": "Driving frequency and amplitude: signal generator, checked on the scope. Coil alignment: coils on a rail or ruler so axes coincide. Coil size and turns: same pair throughout. Nearby metal: removed from the bench.",
   "physicsNeeded": "Faraday's law: emf = −N dΦ/dt with emf = 2π f N B A. On the axis, a dipole model gives B ∝ 1/x³ for x much larger than the coil radius, so plot ln(V) against ln(x); the gradient should approach −3. For small x, use the full on axis loop formula.",
   "slVsHl": "Induction is HL only. At HL, top band work compares the data with the on axis loop formula B = μ0 I R² / 2(R² + x²)^(3/2) and shows where the far field power law starts to hold, and treats the effect of coil resonance.",
   "whereMarksAreLost": "Research design: no oscilloscope method described, so readings are vague. Data analysis: log graph gradient quoted without uncertainty and without saying over which range it was fitted. Evaluation: ignoring that x is measured from coil faces, not coil centres.",
   "dataNote": "Needs a signal generator, two coils and an oscilloscope; misalignment and measuring from the face rather than the centre are the main uncertainties.",
   "verdict": "A strong HL choice if you compare with the on axis formula rather than only fitting a power law. Measure the distance to the coil centres to avoid a hidden offset."
  },
  {
   "id": "falloff-of-induced-emf-with-coil-separation",
   "topic": "D.4",
   "topicName": "Induction",
   "level": "HL",
   "title": "Falloff of induced emf with coil separation",
   "researchQuestion": "How does the peak induced emf in a secondary coil depend on its axial distance from a primary coil driven at 1.0 kHz, over separations of 1 cm to 12 cm?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Axial separation between coil centres, 8 to 10 values from 1 cm to 12 cm, measured with a ruler on a fixed track; 3 readings each.",
   "dependentVariable": "Peak to peak emf across the secondary coil measured on an oscilloscope. Optional calculation of the ratio to the primary voltage.",
   "controlledVariables": "Signal generator frequency and amplitude held constant and monitored on a second channel. Same coils, aligned on a common axis with a clamped track. No iron or metal nearby, and the secondary lead layout unchanged. Same oscilloscope range.",
   "physicsNeeded": "Faraday's law: emf = -N dPhi/dt, with flux from the primary falling with distance, roughly like a dipole field, B proportional to 1/x^3 for large separation. Plot ln(emf) against ln(x): the gradient gives the power law exponent.",
   "slVsHl": "Mostly HL because it relies on flux linkage and induction. A top answer compares the exponent to a model with two regimes (near field and far field) and explains why the exponent changes with x.",
   "whereMarksAreLost": "Research design: separations too coarse or coils not aligned. Data analysis: fitting one power law over a range where the behaviour changes. Evaluation: ignoring stray pickup and the coil's finite size when measuring x.",
   "dataNote": "Needs two coils, a signal generator and an oscilloscope; main uncertainty is defining coil separation and stray pickup at large distance.",
   "verdict": "A good HL choice with a rich log graph and a real model to test. Take it if your school has an oscilloscope, and make it yours by testing what the core material or coil orientation does."
  },
  {
   "id": "hand-cranked-generator-speed-and-peak-voltage",
   "topic": "D.4",
   "topicName": "Induction",
   "level": "HL",
   "title": "Hand-cranked generator speed and peak voltage",
   "researchQuestion": "How does the rotation frequency of a coil in a uniform magnetic field (1 to 8 Hz, 6 values) affect the peak e.m.f. of the generator?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Rotation frequency of a coil, 1 to 8 Hz, controlled by a motor at set voltage or a hand crank with a marked rate. At least 6 frequencies, 3 readings each.",
   "dependentVariable": "Peak e.m.f. from an oscilloscope or datalogger, and frequency from the period of the trace, in Hz. Peak e.m.f. found from the trace amplitude.",
   "controlledVariables": "Coil area and number of turns. Magnetic field, by using the same magnets at the same spacing. Load resistance, using an open circuit or a fixed resistor. Brush contacts and their condition.",
   "physicsNeeded": "e.m.f. = N B A omega sin(omega t), so peak e.m.f. = 2 pi N B A f. Plot peak e.m.f. against f; the gradient is 2 pi N B A, from which B can be extracted and compared with a Hall probe reading.",
   "slVsHl": "Induction is HL only. At HL, a straight line with a gradient that gives B. Top band: discuss the load effect on the terminal voltage, and the frequency read from the same trace so the data are self-consistent.",
   "whereMarksAreLost": "Research design: driving the coil by hand at an uneven rate. Data analysis: stating that the line proves proportionality without checking the intercept. Evaluation: ignoring slip ring noise and the change in loading at high speed.",
   "dataNote": "Needs a small generator kit, a motor and a scope or logger; the main uncertainty is the speed stability when turned by hand.",
   "verdict": "Fine but a bit predictable. Make it personal by using a motor and a Hall probe to compare the B value you deduce with a direct measurement."
  },
  {
   "id": "induced-emf-from-falling-magnets-of-different-strength",
   "topic": "D.4",
   "topicName": "Induction",
   "level": "HL",
   "title": "Induced emf from falling magnets of different strength",
   "researchQuestion": "How does the peak emf induced in a 200 turn coil vary with the surface field strength of four to five magnets (about 20 mT to 400 mT), dropped from a fixed height of 0.20 m?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Magnet type, using ferrite, alnico and neodymium magnets of similar size, plus stacked neodymium discs (1 to 4) to give 5+ field values.",
   "dependentVariable": "Peak emf recorded with a data logger or oscilloscope, five drops per magnet. Field strength measured beforehand with a Hall probe at a fixed distance. Flux change estimated from the area under the emf against time trace.",
   "controlledVariables": "Drop height fixed with a clamped release tube. Same coil and same position in the tube. Magnet orientation with the same pole down. Magnets of similar mass, or mass recorded so speed differences can be corrected.",
   "physicsNeeded": "Faraday's law, emf = -N dΦ/dt. Plot the area under the emf-time curve (which equals NΔΦ) against measured field strength; the gradient relates to the coil area and turns.",
   "slVsHl": "Faraday's law is HL, so this suits HL students. Top marks come from integrating the emf trace, checking that the area matches N times flux, and accounting for differences in magnet speed and mass.",
   "whereMarksAreLost": "Research design: changing several magnet properties at once, such as size and mass. Data analysis: reading only the peak and ignoring the area. Evaluation: not noting that speed changes with magnetic braking.",
   "dataNote": "Needs a logger or oscilloscope, a coil and a Hall probe; the main uncertainty is inconsistent drop and different magnet mass.",
   "verdict": "A good HL choice if you control size and mass carefully. The twist is to use the area under the trace, not just the peak, so that the physics goes beyond a simple comparison."
  },
  {
   "id": "induced-pulse-size-for-a-falling-magnet-against-coil-turns",
   "topic": "D.4",
   "topicName": "Induction",
   "level": "HL",
   "title": "Induced pulse size for a falling magnet against coil turns",
   "researchQuestion": "How does the peak EMF induced when a neodymium magnet falls from a height of 0.20 m through a coil vary with number of turns N from 100 to 1000 in 6 steps?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Number of turns N: 100, 200, 400, 600, 800, 1000 (tap each tapping point on one long coil or use separate coils on the same tube), 5 drops each.",
   "dependentVariable": "Peak EMF from a datalogger or oscilloscope with a voltage sensor, sampling at 1 kHz or above. Also integrate the pulse area to find the total flux change.",
   "controlledVariables": "Drop height, fixed with a release stand and ruler. The same magnet throughout. Tube of same diameter and coil length, avoiding changes to the coil length as N changes by winding in layers. Coil resistance, checked by multimeter and noted.",
   "physicsNeeded": "Faraday's law ε = −N dΦ/dt. Plot peak EMF against N: the gradient is the peak rate of flux change. The area under each pulse should be proportional to N with the same flux Φ.",
   "slVsHl": "Faraday's law is HL (D.4), so this is an HL idea. Top work uses the area under EMF against time to prove flux change is constant, and explains the asymmetric double pulse from the accelerating magnet.",
   "whereMarksAreLost": "Research design: using a multimeter for current, which cannot capture a millisecond pulse, so use a logger. Data analysis: reading peaks with too low a sample rate. Evaluation: not checking that layers of wire change the average area.",
   "dataNote": "Needs a logger with a voltage sensor and 1000 turns of wire; the main uncertainty is sample rate and magnet wobble in the tube.",
   "verdict": "Worth doing at HL, but only with a logger. The pulse area test is the good bit."
  },
  {
   "id": "magnet-fall-height-and-peak-e-m-f-in-a-coil",
   "topic": "D.4",
   "topicName": "Induction",
   "level": "HL",
   "title": "Magnet fall height and peak e.m.f. in a coil",
   "researchQuestion": "How does the release height of a neodymium magnet (5 to 50 cm, 6 heights) affect the peak e.m.f. induced in a 500 turn coil it falls through?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Release height above the coil, 5 to 50 cm, 6 or more values, using a guide tube and 5 drops each.",
   "dependentVariable": "Peak e.m.f. from a datalogger or oscilloscope connected to the coil, in mV. Speed at the coil from v = sqrt(2 g h), checked by timing with a light gate.",
   "controlledVariables": "Magnet, the same one each time and dropped in the same orientation. Coil and number of turns. Circuit resistance and the input of the logger. Alignment through the centre of the coil, using a straight tube.",
   "physicsNeeded": "Faraday's law: e.m.f. = N dPhi/dt, which depends on the speed of the magnet. Plot peak e.m.f. against v, or against sqrt(h). The expectation is a straight line through the origin. Compare the area under the pulse with the total flux change, which should not depend on height.",
   "slVsHl": "Induction is HL only. At HL, plot peak e.m.f. against sqrt(h) and integrate the pulse to check flux linkage. Top band: explain why the graph curves at high speed because of the finite length of the magnet and the coil's response.",
   "whereMarksAreLost": "Research design: dropping the magnet without a guide tube so it tumbles. Data analysis: reading a peak from a slow logger and missing it. Evaluation: not accounting for air drag or the magnetic braking from the coil itself.",
   "dataNote": "Needs a datalogger sampling at 1 kHz or more or a scope; the main uncertainty is the sampling rate and the tilt of the magnet.",
   "verdict": "A good HL choice with clear physics. The twist is to check that the area under each pulse is constant, which gives an independent test of Faraday's law."
  },
  {
   "id": "magnet-falling-through-copper-tubes-of-varying-wall-thickness",
   "topic": "D.4",
   "topicName": "Induction",
   "level": "HL",
   "title": "Magnet falling through copper tubes of varying wall thickness",
   "researchQuestion": "How does the wall thickness of a copper tube, from 0.5 mm to 3.0 mm, affect the time taken by a neodymium magnet to fall 30 cm through it, in seconds?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Wall thickness of copper tube, 5 or 6 values (for example stacked or nested tubes of the same inner diameter, or tubes of differing wall), each dropped 5 times. A plastic tube of the same size is the control.",
   "dependentVariable": "Fall time over a fixed 30 cm, measured with a phone slow-motion video at 240 fps or two light gates. Calculated: terminal speed = distance / time.",
   "controlledVariables": "Magnet: the same one each time, checked for mass. Tube length and inner diameter: measured with calipers. Tube orientation: vertical, checked with a plumb line. Temperature: tubes left to cool between drops.",
   "physicsNeeded": "Faraday's and Lenz's laws: induced eddy currents oppose the motion, giving a drag that grows with wall thickness until saturating. At terminal speed mg = drag. Plot terminal speed against 1/thickness, or drag force mg against thickness, to test the trend.",
   "slVsHl": "Induction is HL content, so this is mainly an HL idea. Top band work explains the non-linear trend, since the field decays through the wall, and estimates drag from mg at terminal speed. Adding a second conductor such as aluminium widens the analysis.",
   "whereMarksAreLost": "Research design: getting varied wall thickness with tubes that also differ in inner diameter. Data analysis: timing errors from hand release and no video calibration. Conclusion: claiming a simple proportionality without testing it. Evaluation: not noting that the magnet may tilt or rub against the tube.",
   "dataNote": "Needs several copper tubes, a strong neodymium magnet and video timing; the main uncertainty is that tubes with different thickness are hard to source with the same bore.",
   "verdict": "Visually striking and good physics, but sourcing suitable tubes is the catch. Personalise it by using a resistivity comparison with aluminium and brass tubes."
  },
  {
   "id": "peak-emf-against-stacked-magnets-dropped-through-a-coil",
   "topic": "D.4",
   "topicName": "Induction",
   "level": "HL",
   "title": "Peak EMF against stacked magnets dropped through a coil",
   "researchQuestion": "How does the peak EMF in a 500-turn coil vary with the number of identical disc magnets stacked together, from 1 to 6, when each stack is dropped from 0.15 m?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Number of stacked neodymium disc magnets: 1, 2, 3, 4, 5, 6. Each stack dropped 5 times.",
   "dependentVariable": "Peak EMF recorded by a voltage sensor and datalogger. Also time between the two peaks to estimate the speed.",
   "controlledVariables": "Drop height and release method, using a stand. Coil turns and geometry, one coil throughout. Stack alignment and pole direction, all facing the same way. Tube friction, using the same smooth plastic tube.",
   "physicsNeeded": "Peak EMF ∝ N dΦ/dt, with dΦ/dt rising with both field and speed. Plot peak EMF against number of magnets, and consider a speed correction since mass changes the fall through eddy currents.",
   "slVsHl": "Induction is HL, so this suits HL. Strong answers separate the effect of field from the change in speed by measuring the timing between peaks, and discuss why the relation is not exactly linear.",
   "whereMarksAreLost": "Research design: 'magnet strength' is not measured, so use the number of magnets and measure B with a probe if possible. Data analysis: ignoring speed change. Evaluation: magnets sticking or tilting in the tube.",
   "dataNote": "Needs a logger, a coil and neodymium discs; the main uncertainty is tilt and speed differences between stacks.",
   "verdict": "Fine at HL, but overlaps with turns idea. I would take this only if you also measure speed, which makes it your own."
  },
  {
   "id": "peak-emf-of-a-hand-spun-coil-against-rotation-frequency",
   "topic": "D.4",
   "topicName": "Induction",
   "level": "HL",
   "title": "Peak EMF of a hand-spun coil against rotation frequency",
   "researchQuestion": "How does the peak EMF induced in a 200-turn coil change as its rotation frequency is varied from 2 Hz to 10 Hz in steps of 2 Hz?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Rotation frequency of the coil, 2, 4, 6, 8 and 10 Hz (5 values, 5 repeats each). Set by a motor driven at known voltages, with frequency measured by a phone slow-motion video or a light gate on the shaft.",
   "dependentVariable": "Peak EMF read from a data logger or oscilloscope connected across the coil via slip rings or brushes. Peak EMF is taken from each trace; the frequency is checked from the period of the trace.",
   "controlledVariables": "Number of turns and coil area: same coil throughout, measured with a ruler. Magnet strength and gap: same pair of magnets, fixed clamp position. Load resistance: use a high-resistance input on the logger so current is negligible. Orientation of coil axis: fixed in the frame.",
   "physicsNeeded": "Faraday's law gives peak EMF = N B A ω, so EMF is proportional to frequency. Plot peak EMF (y) against frequency f (x); gradient = 2πNBA, so B can be extracted and compared with a Hall probe reading. Peak-to-peak EMF is not proportional to time-averaged values, so use the same measure throughout.",
   "slVsHl": "SL students can only do this as a descriptive test of proportionality with limited theory, since induction is HL. HL students derive the gradient, extract B, and compare it with an independent measurement. Top band work also checks the sinusoidal shape and discusses back-EMF and brush contact.",
   "whereMarksAreLost": "Research design: uncontrolled speed because the crank is turned by hand. Data analysis: measuring frequency poorly, no uncertainty on it. Evaluation: not explaining why the EMF trace is distorted or why the gradient differs from the predicted value.",
   "dataNote": "Needs a small motor or crank generator with a logger; the main uncertainty is the rotation frequency and brush noise.",
   "verdict": "Worth choosing for HL if you can get a steady motor. A hand crank gives poor control, so the twist is to calibrate the motor first and extract B from the gradient."
  },
  {
   "id": "pipe-resistivity-and-eddy-current-braking-of-a-magnet",
   "topic": "D.4",
   "topicName": "Induction",
   "level": "HL",
   "title": "Pipe resistivity and eddy current braking of a magnet",
   "researchQuestion": "How does the resistivity of a vertical tube, using copper, aluminium, brass and other metals of the same dimensions, affect the fall time of a neodymium magnet dropped down it from a fixed height?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Tube material (at least 5 tubes, e.g. copper, aluminium, brass, zinc-plated steel, plastic as control), converted to resistivity using tabulated values; 5 drops per tube. Better still, vary resistivity by measuring tubes at different temperatures with ice and warm water.",
   "dependentVariable": "Fall time over a fixed 40 cm section, measured with a slow-motion phone video at 240 fps or two light gates. Terminal speed v = distance/time and the estimated drag force are calculated.",
   "controlledVariables": "Same magnet and orientation, checked by a marker; tubes of matching length, inner diameter and wall thickness measured with vernier callipers; magnet released from the same height on the axis; tubes kept vertical with a plumb line.",
   "physicsNeeded": "Induced emf ε = −dΦ/dt drives eddy currents I = ε/R, so drag force scales roughly as 1/ρ at terminal speed. Plot terminal speed v against ρ, or 1/v against 1/ρ; a straight line supports the model. Wall thickness also matters, so it must be matched.",
   "slVsHl": "An SL student can time falls and show that lower resistivity gives slower falls. Top band work builds a model for the terminal speed, tests the proportionality to ρ, and discusses why tubes of different wall thickness and magnetic permeability spoil the comparison.",
   "whereMarksAreLost": "Research design: tubes differ in wall thickness and diameter, so resistivity is not the only variable. Data analysis: only 3 materials used, so no meaningful graph. Evaluation: magnet tilting, sticking and ignoring the acceleration phase before terminal speed.",
   "dataNote": "Tubes of several metals are costly; buy offcuts or ask the school workshop, and use video analysis, which has an uncertainty of about one frame.",
   "verdict": "A classic that examiners know, but the resistivity angle with a real model is still good. Make it yours by varying the temperature of one tube to get a continuous IV."
  },
  {
   "id": "step-down-transformer-turns-ratio-versus-efficiency",
   "topic": "D.4",
   "topicName": "Induction",
   "level": "HL",
   "title": "Step-down transformer: turns ratio versus efficiency",
   "researchQuestion": "How does the secondary to primary turns ratio (0.25 to 2.0, six values) affect the output voltage and the efficiency of a demountable transformer supplied with 4.0 V AC at 50 Hz?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Number of secondary turns Ns, with primary fixed at 200 turns: 50, 100, 150, 200, 300, 400 turns (ratio 0.25 to 2.0). Three repeats per setting.",
   "dependentVariable": "Secondary RMS voltage Vs and primary and secondary RMS currents, read with digital multimeters (AC). Efficiency = (Vs·Is)/(Vp·Ip) calculated for each ratio.",
   "controlledVariables": "Primary supply voltage (held at 4.0 V RMS, checked with a meter each time); load resistance (same resistor, e.g. 10 Ω, power rating checked); iron core and its clamping (same C-core and same tightness); supply frequency (fixed at 50 Hz from a low-voltage AC supply).",
   "physicsNeeded": "Ideal transformer: Vs/Vp = Ns/Np, and power in equals power out. Plot Vs against Ns, expecting a straight line through the origin with gradient Vp/Np. Then plot efficiency against ratio to see where losses (copper, eddy currents, flux leakage) matter.",
   "slVsHl": "Induction is HL content, so an SL student could treat the ratio law as given but would struggle to justify it. HL depth comes from explaining the losses using Faraday's law and eddy currents, and from testing a laminated core against a solid one.",
   "whereMarksAreLost": "Research design: not stating the load and leaving primary voltage to drift. Data analysis: multimeter AC readings are unreliable with small currents, and uncertainty in efficiency is not propagated. Evaluation: blaming 'losses' without evidence for which loss dominates.",
   "dataNote": "Demountable transformer kit, low-voltage AC supply and two multimeters; the main uncertainty is meter accuracy on AC currents and coil resistance heating during a run.",
   "verdict": "A safe, doable choice, but common in school labs, so the personal twist matters: for example, measure efficiency against load resistance too, or compare core materials. Take care to keep to low voltage."
  },
  {
   "id": "tube-wall-thickness-or-bore-and-magnet-fall-time-in-copper",
   "topic": "D.4",
   "topicName": "Induction",
   "level": "HL",
   "title": "Tube wall thickness or bore and magnet fall time in copper",
   "researchQuestion": "How does the internal diameter of a copper tube (14 to 22 mm, 5 or more tubes) affect the time taken for a 12 mm neodymium magnet to fall 50 cm through it?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Internal diameter of copper tubes of the same length and wall, 5 or 6 sizes from 14 to 22 mm, measured with a calliper. Five drops each.",
   "dependentVariable": "Fall time over the last 50 cm of tube from a video at 240 fps or light gates. Terminal speed = distance / time.",
   "controlledVariables": "Magnet, same one and orientation. Tube material and wall thickness, from the same supplier where possible. Tube temperature, since resistivity changes with it. Tube kept vertical using a plumb line.",
   "physicsNeeded": "The falling magnet induces eddy currents that create a braking force, and at terminal speed the force equals its weight. A larger gap between the magnet and the tube wall weakens the coupling, so speed rises. Plot log v against log of gap, or v against the gap, and look at the trend; the exact law is not simple, so an empirical fit is needed.",
   "slVsHl": "Eddy currents and Lenz's law are in D.4, HL only. At HL, fit an empirical power law and discuss energy dissipated as heat. Top band: compare with a non-conducting tube control to show that the delay comes from induction alone.",
   "whereMarksAreLost": "Research design: only a few tube sizes with no control tube. Data analysis: fitting a straight line where the data are curved. Evaluation: tubes with different wall thickness and alloys changing conductivity as well.",
   "dataNote": "Needs copper tubes of several diameters, which can be costly; the main uncertainty is that tube wall thickness and purity vary between suppliers.",
   "verdict": "Popular and visual, but sources are hard to make consistent. Choose it only if you can find tubes with matching walls, and always include a plastic tube control."
  },
  {
   "id": "winding-temperature-and-transformer-power-efficiency",
   "topic": "D.4",
   "topicName": "Induction",
   "level": "HL",
   "title": "Winding temperature and transformer power efficiency",
   "researchQuestion": "How does the winding temperature of a small step-down transformer, raised from 20 °C to 80 °C in steps of 10 °C, affect its efficiency, calculated as output power divided by input power?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Transformer temperature from 20 °C to 80 °C in 7 steps of 10 °C, each repeated 3 times. Heat in a water bath or with a hairdryer, or cool with ice, using a sealed or bagged transformer.",
   "dependentVariable": "Input and output r.m.s. voltage and current read with four multimeters (or two power meters), with efficiency calculated as P_out/P_in. Winding temperature taken with a thermocouple probe taped to the case.",
   "controlledVariables": "Load resistance fixed with one power resistor; input voltage held constant with a variable AC supply and monitored; frequency fixed at 50 Hz; measurement taken within seconds of switching on so self-heating does not drift the temperature.",
   "physicsNeeded": "Winding resistance rises with temperature, R = R0(1 + αΔT), so copper loss I²R grows. Plot efficiency (or power loss) against temperature; the gradient links to α and the copper loss fraction. Requires transformer efficiency and induction ideas from D.4.",
   "slVsHl": "An SL student can plot efficiency against temperature and describe the trend. Top band work separates copper loss from core loss, extracts a temperature coefficient from the gradient and compares it with the accepted value for copper.",
   "whereMarksAreLost": "Research design: mains transformers are unsafe to heat and immerse, and self-heating during measurement is often ignored. Data analysis: efficiency changes are tiny, often smaller than meter uncertainty, and uncertainties are not propagated. Evaluation: the transformer core temperature is assumed equal to the case temperature.",
   "dataNote": "Needs a low-voltage bench transformer, four meters and a thermocouple; the efficiency change may be within meter resolution, so use the highest-resolution ranges.",
   "verdict": "Risky because the effect is small and easy to drown in noise. Worth it only if you can measure winding resistance directly with a four-wire method as a cross-check, and it needs low-voltage kit only."
  },
  {
   "id": "rydberg-constant-from-hydrogen-lines-using-a-diffraction-grating",
   "topic": "E.1",
   "topicName": "Structure of the atom",
   "level": "both",
   "title": "Rydberg constant from hydrogen lines using a diffraction grating",
   "researchQuestion": "What value of the Rydberg constant, in m⁻¹, do the visible Balmer lines of hydrogen give when measured with a diffraction grating of 600 lines per mm?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Balmer line (transition from n = 3, 4, 5 and 6 to n = 2), so 3 to 4 lines, each measured at both sides of the centre and in first and second order where visible.",
   "dependentVariable": "Diffraction angle read from a spectrometer or measured with a metre rule and a laser-calibrated set-up; wavelength calculated from d sin θ = nλ.",
   "controlledVariables": "Grating: same one, with line spacing calibrated using a laser of known wavelength. Slit width: fixed. Distance from grating to screen: measured and held constant. Lamp: same hydrogen tube, run at steady current.",
   "physicsNeeded": "1/λ = R(1/2² − 1/n²). Plot 1/λ (y) against (1/4 − 1/n²) (x): a straight line through the origin with gradient R.",
   "slVsHl": "SL students can extract R from a gradient and compare with 1.097×10⁷ m⁻¹. Top band work calibrates the grating, uses both sides of the centre to reduce zero error, and examines the fit residuals. HL depth can come from using energy level ideas and the discussion of the Bohr model.",
   "whereMarksAreLost": "Research design: relying on a nominal grating spacing. Data analysis: fitting through the origin without justification. Evaluation: the dim red and violet lines are hard to see, which is rarely discussed.",
   "dataNote": "Needs a hydrogen discharge tube with power supply, a grating and a spectrometer or a ruler set-up; the main uncertainty is locating the centre of dim lines.",
   "verdict": "Well suited to a school lab and it gives a numerical answer that can be judged against a known value. Reasonable choice, though the RQ is best written as a value, not a vague 'consistency'."
  },
  {
   "id": "planck-s-constant-from-led-current-voltage-curves",
   "topic": "E.2",
   "topicName": "Quantum physics",
   "level": "HL",
   "title": "Planck's constant from LED current-voltage curves",
   "researchQuestion": "What value of h results from the threshold voltage of six LEDs with peak wavelengths between 450 nm and 950 nm, and how much does the threshold definition change it?",
   "dataDifficulty": 1,
   "dataSource": "experiment",
   "sitesListingIt": 2,
   "independentVariable": "LED colour, six to eight LEDs from infrared to blue, characterised by peak wavelength measured with a diffraction grating or a spectrometer.",
   "dependentVariable": "Threshold voltage from a slowly varied power supply with a voltmeter and a milliammeter, found by extrapolating the linear part of the I–V curve to zero current and, for comparison, at a fixed current such as 1 mA. Calculate eV and 1/λ.",
   "controlledVariables": "Series resistor of 100 Ω kept in every circuit. Same voltmeter range and meter. Dark room for judging emission if used. LEDs at room temperature by letting them cool between readings. Same current step size for each LED.",
   "physicsNeeded": "Photon energy eV = hc/λ so V is proportional to 1/λ. Plot V against 1/λ. Gradient is hc/e so h = gradient × e/c.",
   "slVsHl": "This is HL content since it uses photon energy and quantum ideas. Stronger work compares two threshold methods, gives an intercept discussion because the graph should pass through the origin, and explains why h comes out too low or high.",
   "whereMarksAreLost": "Data analysis: reading the voltage where light is first seen by eye, which depends on the observer. Evaluation: not linking the systematic error to the band gap versus emitted photon energy, and ignoring the spread of LED wavelengths. Research design: no measurement of the wavelength, using the value quoted on the packet.",
   "dataNote": "Needs LEDs, a variable supply, two meters and a diffraction grating; the main uncertainty is defining the threshold and the LED's spectral width.",
   "verdict": "A good HL choice that is fairly common, so the comparison of threshold methods makes it yours. Measure the wavelength yourself and give the systematic difference."
  },
  {
   "id": "graphite-atomic-spacing-from-electron-diffraction-rings",
   "topic": "E.2",
   "topicName": "Quantum physics",
   "level": "HL",
   "title": "Graphite atomic spacing from electron diffraction rings",
   "researchQuestion": "What is the spacing between carbon lattice planes in graphite, found from the ring diameters of an electron diffraction tube at accelerating voltages of 2.5 to 5.0 kV?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Accelerating voltage, 2.5 to 5.0 kV in 0.5 kV steps, giving six values, with inner and outer ring diameters measured each time, 5 readings per ring.",
   "dependentVariable": "Ring diameter on the screen, measured with vernier calipers or a transparent ruler in mm; the electron wavelength calculated from voltage; plane spacing d found from the ring angle.",
   "controlledVariables": "Same tube and screen distance; filament heater voltage; room darkness for a clear ring; measurement always taken at the same ring edge.",
   "physicsNeeded": "de Broglie: λ = h/√(2meV). Diffraction: 2d sinθ = nλ, and for small angles the ring radius r ≈ (L/d)λ times a constant. Plot ring diameter against 1/√V. The gradient gives the spacing d, with two values for two rings.",
   "slVsHl": "Wave properties of matter are HL only. An HL student can go beyond simple calculation by comparing d with the accepted values of 0.123 nm and 0.213 nm and treating the tube geometry critically.",
   "whereMarksAreLost": "Research design: the geometry constant is assumed without checking. Data analysis: ring edges are fuzzy, so uncertainty is underestimated. Conclusion: no comparison with literature values.",
   "dataNote": "Needs an electron diffraction tube and EHT supply, usually only available in some schools; the main uncertainty is blurred ring edges, and simulation is a fallback.",
   "verdict": "An excellent HL choice if your school has the tube. Otherwise use a simulation with clear honesty about that."
  },
  {
   "id": "light-colour-and-solar-cell-electrical-output",
   "topic": "E.2",
   "topicName": "Quantum physics",
   "level": "HL",
   "title": "Light colour and solar cell electrical output",
   "researchQuestion": "How does the peak wavelength of LED illumination (from about 450 nm to 650 nm, using 6 colours) affect the power output of a small silicon solar cell at fixed photon flux?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "LED colour or wavelength from about 450 nm to 650 nm (blue, green, yellow, orange, red and one more, checking the datasheet peak wavelength); each repeated 3 times, or use coloured filters over a white lamp.",
   "dependentVariable": "Short-circuit current and open-circuit voltage from a multimeter, or power across a fixed load. Compare with the photon rate, calculated from the light power (from a calibrated sensor) as P/(hc/λ).",
   "controlledVariables": "Distance from LED to cell fixed with a rail; LED drive current kept constant with a series resistor and checked; ambient light excluded with a dark tube; cell temperature and angle fixed.",
   "physicsNeeded": "Photon energy E = hf = hc/λ. If each photon produces one electron, current is proportional to photon rate, not to frequency, so at equal power the current should rise with λ until the band gap cutoff near 1100 nm. Plot current per unit incident power against λ.",
   "slVsHl": "An SL student would struggle to link the response to photon energy. An HL student can test the one-photon-one-electron model and analyse the spectral response, discussing the band gap and thermalisation losses.",
   "whereMarksAreLost": "Research design: LEDs have different intensities, so frequency is confounded with power. Data analysis: no calibration of incident power. Conclusion: claiming that higher frequency gives more output without a physical model.",
   "dataNote": "Needs LEDs, a light sensor or a calibrated reference cell; the main uncertainty is the different intensity of each LED, so measure it.",
   "verdict": "Very good if you fix the photon flux or normalise by incident power, and weak if you just swap LEDs. The normalisation is the whole point."
  },
  {
   "id": "planck-s-constant-from-led-turn-on-and-photoelectric-stopping-voltage",
   "topic": "E.2",
   "topicName": "Quantum physics",
   "level": "HL",
   "title": "Planck's constant from LED turn-on and photoelectric stopping voltage",
   "researchQuestion": "How does the frequency of light, from about 4.3×10¹⁴ Hz to 7.5×10¹⁴ Hz, affect the stopping potential of a photocell, in volts, and what value of Planck's constant follows?",
   "dataDifficulty": 3,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Frequency of light, 5 to 7 values, set using narrowband filters or LEDs of known peak wavelength, each measurement repeated 3 times.",
   "dependentVariable": "Stopping potential, measured with a digital voltmeter across a photocell or a commercial photoelectric apparatus. Calculated: the gradient of V_s against f, then h = gradient × e.",
   "controlledVariables": "Light intensity: same lamp and distance, monitored with a lux meter. Photocathode: same cell throughout. Ambient light: apparatus in a darkened box. Warm-up time: fixed before each reading.",
   "physicsNeeded": "eV_s = hf − φ. Plot V_s (y) against f (x): gradient = h/e, y-intercept = −φ/e, x-intercept gives the threshold frequency.",
   "slVsHl": "Photoelectric effect is HL content, so this suits HL. Top band work compares h and φ with accepted values, quantifies uncertainty via maximum and minimum gradients, and discusses why the voltage reading drifts as the cell charges.",
   "whereMarksAreLost": "Research design: using LED wavelengths from a datasheet without checking the spread. Data analysis: reading the stopping voltage at an ill-defined point on the curve. Evaluation: not addressing the contact potential and the leakage current.",
   "dataNote": "Needs a photoelectric apparatus or vacuum photocell with a high-impedance voltmeter; the main uncertainty is defining the stopping voltage and the wide spectrum of filtered light.",
   "verdict": "Fine physics and it gives a very clean gradient if the equipment works. If your school has no photocell, do not fake it; use the LED turn-on voltage method as a clearly labelled alternative."
  },
  {
   "id": "work-function-of-a-metal-from-led-stopping-voltages",
   "topic": "E.2",
   "topicName": "Quantum physics",
   "level": "HL",
   "title": "Work function of a metal from LED stopping voltages",
   "researchQuestion": "What is the work function of a metal, in eV, found from stopping potentials measured with light frequencies from 5.0 × 10¹⁴ to 8.0 × 10¹⁴ Hz?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Light frequency, from 5 to 6 filters or coloured LEDs (red to violet) covering 5.0 to 8.0 × 10¹⁴ Hz, using known wavelengths from a spectrometer; 5 readings each.",
   "dependentVariable": "Stopping potential in V from a high-impedance voltmeter across a photocell; the work function found from the intercept of the graph.",
   "controlledVariables": "Same photocell and distance from source; same light intensity, checked with a lux meter; dark room; same warm-up time for LEDs.",
   "physicsNeeded": "Einstein: eVs = hf − φ. Plot stopping potential against frequency: the gradient is h/e and the intercept on the vertical axis is −φ/e. The gradient checks against h/e = 4.14 × 10⁻¹⁵ V s.",
   "slVsHl": "Photoelectric effect is HL only. Extra depth: use the gradient as an independent test of h, and consider why LED bandwidth widens the uncertainty on frequency.",
   "whereMarksAreLost": "Research design: LED wavelength taken from the packaging rather than measured. Data analysis: stopping voltage read while still drifting. Evaluation: the contact potential is not discussed.",
   "dataNote": "Needs a photocell or photoelectric kit and voltmeter; the main uncertainty is the wavelength spread of LEDs and slow voltage drift.",
   "verdict": "Good, classic and worth doing. It is a physics measurement, so do it carefully and compare h with the known value."
  },
  {
   "id": "absorption-of-beta-and-gamma-radiation-by-aluminium-and-lead",
   "topic": "E.3",
   "topicName": "Radioactive decay",
   "level": "both",
   "title": "Absorption of beta and gamma radiation by aluminium and lead",
   "researchQuestion": "How does the thickness of aluminium sheet (0 to 4 mm, 8 values) affect the corrected count rate of a Sr-90 beta source at a fixed 5 cm from a Geiger tube?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 4,
   "independentVariable": "Thickness of aluminium absorber, 0 to 4 mm, at least eight values from stacked sheets measured with a micrometer. Alternatively lead for gamma. Repeat each count three times.",
   "dependentVariable": "Counts in 120 s with a Geiger-Müller tube and counter, divided by time. Subtract the background count rate measured before and after (about 20 minutes total). Calculate the uncertainty as √N.",
   "controlledVariables": "Source to detector distance, fixed with a clamp. The same source and tube with the same voltage. Absorber positioned at the same place. Count time long enough for over 400 counts at the lowest rate.",
   "physicsNeeded": "Exponential attenuation, I = I₀e^(−μx). Plot ln(corrected rate) against x. The gradient is −μ, and the half-value thickness is ln2/μ. For beta the curve is only approximately exponential, so discuss range.",
   "slVsHl": "SL students can plot ln R against thickness and find μ. Top marks require proper Poisson uncertainty, error bars on the ln plot and a discussion of why beta is not truly exponential. HL adds nothing needed but the link to nuclear physics is nice.",
   "whereMarksAreLost": "Research design: short counting times giving large √N errors. Data analysis: background not subtracted, or uncertainties in ln values ignored. Conclusion: claiming pure exponential for beta. Evaluation: source distance and absorber gaps not discussed. Also this is a very common topic (four sources) so examiners expect more. Safety and school licence rules for sources need to be handled by the teacher.",
   "dataNote": "Needs a sealed source and GM tube from school, so you may only have access under the teacher; the main uncertainty is count statistics.",
   "verdict": "Very overdone, so it needs a twist. Try comparing several materials with one thickness in g cm⁻² to show mass thickness matters, or use a simulation or open dataset if no source is available."
  },
  {
   "id": "effect-of-counting-time-on-decay-constant-precision",
   "topic": "E.3",
   "topicName": "Radioactive decay",
   "level": "both",
   "title": "Effect of counting time on decay constant precision",
   "researchQuestion": "How does the counting interval, from 5 s to 60 s, affect the percentage uncertainty in the decay constant of a Ba-137m source fitted over 10 minutes?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Counting interval, 5 values (5, 10, 20, 40 and 60 s), with the same source data set binned in different ways or with separate runs.",
   "dependentVariable": "Counts recorded by a Geiger-Müller tube and scaler, with background subtracted; the decay constant λ calculated from the gradient of ln(A) against time, and the uncertainty in it taken from the fit.",
   "controlledVariables": "Source and tube geometry: fixed with a clamp at set distance. Background: measured for 10 minutes before and after. Voltage on the tube: kept at the operating value. Total elapsed time: same for every interval.",
   "physicsNeeded": "N = N₀e^(−λt), so ln(count rate) against t is linear with gradient −λ. Counting error is √N, so the uncertainty on ln(rate) is about 1/√N. Compare λ with ln 2 / 2.55 min.",
   "slVsHl": "SL students can fit the decay and compare with the accepted half-life. Top band work propagates the Poisson uncertainties into weighted fits and shows how the precision scales with the interval. HL depth is not syllabus-specific, but the statistics adds sophistication.",
   "whereMarksAreLost": "Research design: forgetting the background and not repeating the run. Data analysis: taking logs of low counts without treating the error bars. Evaluation: ignoring dead time and the source running out during the experiment.",
   "dataNote": "Needs a protactinium or Ba-137m generator kit, a GM tube and a counter; the main uncertainty is the low count rate at long times.",
   "verdict": "Good if you have access to a short-half-life source, and the statistics gives a distinct angle. If the school only has long-lived sources, do it as a simulation and say so."
  },
  {
   "id": "testing-inverse-square-fall-off-with-a-gamma-source",
   "topic": "E.3",
   "topicName": "Radioactive decay",
   "level": "both",
   "title": "Testing inverse square fall off with a gamma source",
   "researchQuestion": "Does the corrected count rate from a sealed gamma source follow an inverse square law for distances between 3 cm and 30 cm from a GM tube?",
   "dataDifficulty": 2,
   "dataSource": "experiment",
   "sitesListingIt": 1,
   "independentVariable": "Distance from source to tube window: 3, 5, 8, 12, 16, 20, 25, 30 cm (8 values), each measured from the centre of the source to the sensitive element, with count times of 2 to 5 minutes.",
   "dependentVariable": "Counts recorded over a timed interval with a GM tube and scaler, converted to count rate in counts per second. Background is measured for 10 minutes before and after, and subtracted. The uncertainty is taken as √N.",
   "controlledVariables": "Same source and same tube, fixed on a rail. Background measured at the same location. Source and tube axes aligned. Counting time chosen so that every point has at least 1000 counts where possible.",
   "physicsNeeded": "For a point source, corrected rate ∝ 1/(x + x₀)², where x₀ is the unknown offset to the effective centre of the tube and source. Plot 1/√(corrected rate) against x; it should be a straight line, and the negative x intercept gives the offset.",
   "slVsHl": "SL: plot rate against 1/x² and comment on linearity. Top band: use the 1/√R against x method to find the hidden offset and quantify it, and discuss the tube's dead time. HL and SL alike gain from a proper treatment of Poisson uncertainty.",
   "whereMarksAreLost": "Research design: safety and source handling not considered, or too short counting times. Data analysis: forgetting to subtract background or using distance from the case, not the source. Conclusion: claiming an exact power of 2 with no uncertainty on the gradient. Evaluation: ignoring absorption in air and the finite size of the source and tube.",
   "dataNote": "Needs a school GM tube, scaler and a sealed source from the physics department, handled by the technician; the main uncertainty is the source to tube offset and low counts at large distance.",
   "verdict": "A good option if your school holds a source. The offset method is what lifts it from a routine check to real analysis."
  },
  {
   "id": "blackbody-fits-to-archive-spectra-for-star-temperatures",
   "topic": "E.5",
   "topicName": "Fusion and stars",
   "level": "both",
   "title": "Blackbody fits to archive spectra for star temperatures",
   "researchQuestion": "How closely does the temperature found from Wien's law applied to archive spectra of 8 to 12 stars with published temperatures between 3500 K and 10000 K agree with the catalogue values, in percentage difference?",
   "dataDifficulty": 2,
   "dataSource": "database",
   "sitesListingIt": 1,
   "independentVariable": "Published catalogue temperature of each star, 8 to 12 stars spanning about 3500 K to 10000 K, chosen from one archive so the spectra are reduced in the same way.",
   "dependentVariable": "Peak wavelength read from each flux calibrated spectrum with a spreadsheet or Python, giving temperature from lambda_max = b/T; percentage difference from the catalogue value is then calculated.",
   "controlledVariables": "Same archive and instrument for every spectrum, so calibration is alike. Same wavelength range used when locating the peak. Same smoothing window applied to every spectrum. Stars chosen with little reddening, so dust does not shift the peak.",
   "physicsNeeded": "Wien's displacement law lambda_max = b/T and the Stefan-Boltzmann relation for stars. Plot lambda_max against 1/T_catalogue, expecting a straight line through the origin with gradient b = 2.898e-3 m K. HL students may fit the full Planck curve.",
   "slVsHl": "SL: peak reading, the graph and a percentage comparison. Top band: fit the Planck function, compare it with the peak method, and explain why stellar spectra with absorption lines and limited wavelength coverage bias the peak. HL: propagate fit uncertainties.",
   "whereMarksAreLost": "Research design: no reason given for choosing these stars or archive. Data analysis: peak read by eye with no uncertainty. Conclusion: agreement claimed without a percentage difference. Evaluation: ignores that stars are not perfect blackbodies and that the spectrum may not cover the peak.",
   "dataNote": "Needs a public spectral archive and a spreadsheet or Python; the main uncertainty is the peak position where the spectrum is noisy or truncated.",
   "verdict": "Worth choosing if you like data work and want astrophysics without a telescope. Make it your own by picking a themed sample, such as stars from one constellation or cluster, and being listed on only one site means examiners have not seen it often."
  },
  {
   "id": "estimating-the-hubble-constant-from-a-galaxy-catalogue",
   "topic": "E.5",
   "topicName": "Fusion and stars",
   "level": "both",
   "title": "Estimating the Hubble constant from a galaxy catalogue",
   "researchQuestion": "What value of the Hubble constant, in km s⁻¹ Mpc⁻¹, follows from a linear fit of recession speed against distance for 20 to 30 galaxies within 300 Mpc?",
   "dataDifficulty": 1,
   "dataSource": "database",
   "sitesListingIt": 1,
   "independentVariable": "Distance to the galaxy, 20 to 30 galaxies spread from about 10 Mpc to 300 Mpc, taken from a public database.",
   "dependentVariable": "Recession speed calculated from redshift, v = cz for small z; the Hubble constant found as the gradient of v against d.",
   "controlledVariables": "Distance method: one indicator only, such as Type Ia supernovae. Data source: one database (for example NED). Redshift range: below 0.1, so the low-speed formula holds. Peculiar velocities: nearby galaxies excluded.",
   "physicsNeeded": "v = H₀d. Plot v (y) against d (x): gradient H₀, and 1/H₀ gives an approximate age of the universe. Compare with about 70 km s⁻¹ Mpc⁻¹.",
   "slVsHl": "SL students can get a straight line and a value with an uncertainty from the gradient. Top band work compares the results for different distance indicators and explains the scatter in terms of peculiar velocity. HL depth can come from using the relativistic Doppler formula at higher redshift.",
   "whereMarksAreLost": "Research design: mixing distance methods and not stating the selection criteria. Data analysis: no uncertainty on the gradient and ignoring outliers without reasoning. Evaluation: forgetting that the local scatter does not reflect the measurement quality.",
   "dataNote": "Needs only a spreadsheet and free online catalogue data; the main uncertainty is the systematic error in the distance ladder.",
   "verdict": "Easy data, but it is a popular choice, so it needs a twist. Compare two distance indicators or two redshift ranges, and explain why the results disagree."
  },
  {
   "id": "planet-size-from-public-transit-light-curve-data",
   "topic": "E.5",
   "topicName": "Fusion and stars",
   "level": "both",
   "title": "Planet size from public transit light curve data",
   "researchQuestion": "How does the fractional dip in brightness in TESS or Kepler light curves for 6 to 8 known exoplanets compare with the value predicted from published planet and star radii?",
   "dataDifficulty": 2,
   "dataSource": "database",
   "sitesListingIt": 1,
   "independentVariable": "Exoplanet system, 6 to 8 targets chosen with transit depths from about 0.3% to 3%.",
   "dependentVariable": "Transit depth from the flux drop in downloaded light curve data, found with a spreadsheet or Python; planet radius calculated as R_p = R_star × √depth.",
   "controlledVariables": "Data source: same mission and same pipeline for every target. Data quality: only targets with a clear, high signal-to-noise transit. Detrending: the same method applied throughout. Stellar radius: taken from one catalogue.",
   "physicsNeeded": "Depth ≈ (R_p/R_star)². Plot measured depth (y) against (published R_p/R_star)² (x): a line through the origin with gradient 1. Duration relates to orbital speed via v = 2πa/T.",
   "slVsHl": "SL students can measure depths and compare radii. Top band work handles the noise, limb darkening and the propagation of uncertainty. HL depth can come from using Kepler's third law with orbital period to get the orbit radius and the star's mass.",
   "whereMarksAreLost": "Research design: choosing targets without stating criteria. Data analysis: reading the depth by eye and giving no uncertainty. Evaluation: not discussing stellar variability and limb darkening.",
   "dataNote": "Uses free archive data such as the NASA Exoplanet Archive or MAST, and a spreadsheet; the main uncertainty is the noise in the baseline flux.",
   "verdict": "A good database study with real data. Twist: choose systems with a range of sizes, including one small planet where the noise matters, and be honest about it."
  },
  {
   "id": "testing-l-4-r-t-with-catalogued-stellar-data",
   "topic": "E.5",
   "topicName": "Fusion and stars",
   "level": "both",
   "title": "Testing L = 4πR²σT⁴ with catalogued stellar data",
   "researchQuestion": "For about 40 main-sequence and giant stars from a catalogue, does the luminosity follow L proportional to R²T⁴ with a fitted constant close to 4πσ, using surface temperatures from 3000 K to 30 000 K?",
   "dataDifficulty": 2,
   "dataSource": "database",
   "sitesListingIt": 1,
   "independentVariable": "Star's R²T⁴, calculated for 30 to 40 stars spanning 3000 to 30 000 K, chosen from the Hipparcos or Gaia catalogue via SIMBAD or VizieR.",
   "dependentVariable": "Luminosity in watts, found from the catalogued absolute magnitude or from apparent brightness and parallax distance. Radius is taken from the catalogue's interferometric or angular diameter values.",
   "controlledVariables": "Selection rule: stars with parallax error below 5 percent, one catalogue for all values. Stellar type: separate main sequence and giants when plotting. Data source: the same catalogue release. Units: converted to SI once at the start.",
   "physicsNeeded": "The Stefan-Boltzmann law L = 4πσR²T⁴. Plot L (y) against R²T⁴ (x); gradient should equal 4πσ = 7.12×10⁻⁷ W m⁻² K⁻⁴. A log-log plot of L against T at fixed R also gives an exponent of 4.",
   "slVsHl": "SL students plot the graph and compare the gradient with 4πσ. Depth comes from uncertainties in distance, radius and temperature, and discussing why hotter stars are not always brighter, since radius matters. The original claim that brighter means hotter is wrong, so fix it.",
   "whereMarksAreLost": "Research design: choosing stars without a stated rule, or plotting L against T only, which does not test the law. Data analysis: log plots without uncertainties. Evaluation: not discussing that stars are not perfect black bodies.",
   "dataNote": "Needs a spreadsheet and free catalogue access; the main uncertainty is the catalogued radius and temperature.",
   "verdict": "Good database study if you fix the flawed idea that luminosity simply rises with temperature. Testing the constant is what makes it personal and worth choosing."
  }
 ]
}