IB Physics IA Ideas: Waves and the Doppler effect

43 of 43 ideas

C.2 Wave model: 8 ideas

Foam and fabric layers reducing sound level

Research question. 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?

C.2 Wave model
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Number of foam layers N, 0, 1, 2, 4, 6, 8, five recordings each.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Light transmission through stacked glass slides

Research question. How does the transmitted light intensity change as the number of identical glass slides in a stack increases from 1 to 8?

C.2 Wave model
SL and HL
Needs care
Rarely listed

My take. A good clean investigation if you handle reflection. That distinction is the twist that separates a good report from a naive one.

Method, physics and where marks are lost+

Independent variable: Number of identical glass microscope slides in the stack, 1 to 8 (8 values), 3 repeats each.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Lux meter or light sensor, lamp and slides; the main uncertainty is stray light and lamp drift.

Sound intensity loss through air against frequency, 200 to 1000 Hz

Research question. 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?

C.2 Wave model
SL and HL
Hard data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Sound level from a speaker over distance

Research question. 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?

C.2 Wave model
SL and HL
Needs care
Rarely listed

My take. Easy but the trap is reflections. Do it outdoors on a field and compare to a run indoors as a twist.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: Sound level in dB from a calibrated meter, converted to intensity using I = I0 × 10^L/10 with I0 = 10⁻¹² W m⁻².
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a sound level meter or a calibrated phone app and a large open space; the main uncertainty is echoes and background noise.

Sound speed in water as it warms

Research question. How does the speed of ultrasound in water change as its temperature rises from 10 °C to 60 °C in steps of 10 °C?

C.2 Wave model
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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).
SL and HL: 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.
Where marks are lost: 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.
Data: Needs an ultrasound pair and an oscilloscope or data logger; the main uncertainty is a short path length giving a small time delay.

Sunscreen layer thickness and UV transmission

Research question. 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?

C.2 Wave model
SL and HL
Hard data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a UV sensor and a precise balance; the main uncertainty is spreading an even film and the sensor's spectral response.

Tray depth and ripple speed in shallow water

Research question. 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?

C.2 Wave model
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Slinky pulse speed and a length that should not matter

Research question. 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?

C.2 Wave model
SL and HL
Easy data
Original: not listed elsewhere

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

C.3 Wave phenomena: 33 ideas

Refractive index of sugar solutions as a concentration probe

Research question. 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?

C.3 Wave phenomena
SL and HL
Needs care
Overdone: on 4 sites

My take. 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.

Method, physics and where marks are lost+

Independent variable: Sugar mass fraction 0, 5, 10, 15, 20, 25, 30, 35, 40% (9 values), 3 measurements of the angle pair at each.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a laser, a semicircular tank and a protractor; angle reading (about ±0.5°) limits how small a concentration change can be seen.

Testing Malus's law with a rotating analyser and a light sensor

Research question. 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)?

C.3 Wave phenomena
SL and HL
Easy data
Overdone: on 4 sites

My take. 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.

Method, physics and where marks are lost+

Independent variable: Analyser angle, 0° to 180° in 10° steps (19 values), read from a protractor mount. Three full rotations to give repeats.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Angular width of the central maximum for single-slit diffraction

Research question. 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?

C.3 Wave phenomena
SL and HL
Needs care
Common: on 2 sites

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Colour dependence of refractive index in a glass prism

Research question. 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?

C.3 Wave phenomena
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Deviation of a ray through a glass prism

Research question. 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?

C.3 Wave phenomena
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Angle of incidence i on the first face, 9 values from 30° to 70°, each repeated 3 times.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: A laser, a prism, a protractor and paper are enough, and the main uncertainty is the thickness of the ray when marking angles.

Diffraction gratings and the precision of wavelength values

Research question. 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?

C.3 Wave phenomena
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Grating line density, 4 to 5 gratings from 100 to 1000 lines/mm; measure orders 1 and 2 for each, 3 repeats.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Focal length and magnification of thin lenses

Research question. 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?

C.3 Wave phenomena
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: An optical bench, lenses and a screen are enough, and the main uncertainty is judging the sharpest image.

Focal length of concave mirrors of different radius

Research question. 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?

C.3 Wave phenomena
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: You need several mirrors with known radius, which is the hard part; the sharpness judgement gives about 1 to 2 cm uncertainty.

Focal length of lenses against lens curvature

Research question. 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?

C.3 Wave phenomena
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Fringe count against mirror displacement in a Michelson interferometer

Research question. 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?

C.3 Wave phenomena
HL topic
Hard data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: Number of fringes N passing a reference mark, counted by eye or from video at 60 fps; wavelength λ = 2Δd/N is calculated.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs an interferometer kit or a home-built one with a laser and beam splitter; alignment and vibrations are the main issues.

Fringe spacing against screen distance for a laser double slit

Research question. 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?

C.3 Wave phenomena
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Slit to screen distance D, 0.80 to 3.00 m in 8 values, measured with a tape; 3 fringe measurements at each distance.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a laser, a double slit slide and a metre rule; the main uncertainty is locating fringe centres.

Fringe spacing against slit separation with a laser

Research question. 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?

C.3 Wave phenomena
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Fringe spacing from a double slit at several wavelengths

Research question. 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?

C.3 Wave phenomena
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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).
Where marks are lost: 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.
Data: Needs laser pointers, a multi-slit slide and a metre rule; the main uncertainty is locating fringe centres.

Fringe spacing in Young's double slit for different colours

Research question. 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?

C.3 Wave phenomena
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Grating diffraction with tilted incidence

Research question. 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?

C.3 Wave phenomena
HL topic
Needs care
Rarely listed

My take. A good twist on a very common grating experiment. Choose it if you like geometry, and derive the modified equation yourself.

Method, physics and where marks are lost+

Independent variable: Angle of incidence on the grating, six values, set on a rotating stage or protractor base.
What you measure: 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.
Controlled variables: 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.
Physics and graph: d(sinθm - sinθi) = mλ. Plot sinθm against sinθi, expected gradient of 1 and intercept of λ/d. Use it to find the wavelength.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a laser, grating and a rotating stage; the main uncertainty is aligning the zero angle to about 1°.

Laser wavelength from Michelson fringe counting

Research question. 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?

C.3 Wave phenomena
SL and HL
Hard data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Mirror displacement d, 6 values from 0.05 to 0.30 mm, set with a micrometer drive, each repeated 3 times.
What you measure: Number of fringes N passing a marked point, counted by eye or on video. Wavelength is calculated from λ = 2d/N.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Law of reflection tested on plane, curved and rough mirrors

Research question. 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?

C.3 Wave phenomena
SL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a laser pointer or ray box, a mirror and a protractor; the main uncertainty is reading the angle to about 1 degree.

Line spacing of gratings and the angles of laser maxima

Research question. 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?

C.3 Wave phenomena
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Grating line density, at least five values from 100 to 1000 lines/mm, or use several gratings and different laser colours as extra data.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a laser pointer, gratings and a metre rule; the main uncertainty is reading the centre of a wide spot at the screen.

Loudness minima spacing from two loudspeakers and wavelength

Research question. 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?

C.3 Wave phenomena
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Speaker separation d: 0.20, 0.30, 0.40, 0.50, 0.60 m (5 values), each measured with a metre rule.
What you measure: 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.
Controlled variables: 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.
Physics and graph: Double-source interference: y = λD/d. Plot y against 1/d. The gradient is λD, so λ = gradient/D, then speed v = fλ.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs two speakers, a generator and a microphone app; minima are broad, so position uncertainty is often ±2 cm.

Magnification of a converging lens against object distance

Research question. 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?

C.3 Wave phenomena
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs an optical bench, a lens and a screen; the main uncertainty is locating the sharpest focus, about 1 to 2 cm.

Malus's law with crossed polarising filters at varied angles

Research question. 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?

C.3 Wave phenomena
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Angle between transmission axes of two polarisers, 0° to 180° in 15° steps (13 values), measured on a protractor mount, with three readings each.
What you measure: Intensity from a light sensor or lux meter (or phone light sensor) in a dark enclosure, with dark background subtracted (lux).
Controlled variables: 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.
Physics and graph: 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).
SL and HL: 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.
Where marks are lost: 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.
Data: Two polarising sheets, a lux meter or phone sensor and a dark box are enough; the main uncertainty is stray light and angle reading.

Measuring a hair's thickness from a laser diffraction pattern

Research question. 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?

C.3 Wave phenomena
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: Distance between the n-th minima measured with a ruler on the screen; calculate the hair width from d = n λ D / y and compare with a micrometer reading.
Controlled variables: Laser wavelength checked from the label; hair position fixed in the beam; darkened room; screen kept perpendicular to the beam.
Physics and graph: Babinet's principle gives the same minima as a single slit of the same width: a sin(θ) = n λ. Plot the fringe spacing against D; gradient equals λ/a, so a = λ/gradient.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Measuring a laser wavelength with several gratings

Research question. 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?

C.3 Wave phenomena
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Newton's rings radius and the wavelength of light

Research question. 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?

C.3 Wave phenomena
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Ring number n from 1 to 10 (10 values), measured on each side of the centre, 3 repeats of the full set.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a travelling microscope, sodium lamp, plano-convex lens and glass plate; the largest error is counting rings and locating edges.

Reflected colour and thickness of soap-film interference

Research question. 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?

C.3 Wave phenomena
HL topic
Hard data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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°.
What you measure: Reflected intensity from a light sensor or phone video of pixel brightness (arbitrary units), plotted against time or angle, with fringe counts.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a laser, a stable vertical film and a light sensor; the main uncertainty is unknown, changing thickness.

Reflected intensity of p-polarised light and Brewster's angle

Research question. 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?

C.3 Wave phenomena
HL topic
Hard data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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(θ_B) = n.
Controlled variables: Same laser and power; polariser orientation fixed; darkened room with background subtracted; detector distance and aperture fixed.
Physics and graph: At Brewster's angle p-polarised light is not reflected, and tan(θ_B) = n. Plot R against angle and locate the minimum, then compare n with a value from Snell's law.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a laser, polariser, turntable and a light sensor; the uncertainty is the angle setting and sensor linearity.

Reflected laser intensity from transparent blocks of varying refractive index

Research question. 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?

C.3 Wave phenomena
SL and HL
Hard data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Refractive index and critical angle of transparent blocks

Research question. 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?

C.3 Wave phenomena
SL and HL
Easy data
Rarely listed

My take. Very common, so it needs a twist. The sugar concentration series gives a clear trend and makes it more personal than comparing blocks.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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).
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Blocks, laser, protractor and a semicircular tank are enough; angle reading uncertainty of about 1° is the limit.

Refractive index of liquids from a hollow prism

Research question. 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?

C.3 Wave phenomena
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Ripple tank slit diffraction in salt solutions of varying density

Research question. 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?

C.3 Wave phenomena
SL and HL
Hard data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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(θ) and compare with λ/b.
Controlled variables: 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.
Physics and graph: Single slit: sin(θ) = λ/b. Wave speed in shallow liquid depends on depth and on surface tension, so density changes wavelength at fixed frequency. Plot sin(θ) against λ (gradient 1/b), or λ against density.
SL and HL: SL students measure angle and wavelength and test λ/b. Top band work explains why the effect is small, compares with shallow water theory and treats surface tension as a hidden variable.
Where marks are lost: 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.
Data: 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.

Single-slit central maximum width at three laser wavelengths

Research question. 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?

C.3 Wave phenomena
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs lasers, adjustable slits and a long screen distance; the main uncertainty is where the minima sit and the true slit width.

Single-slit sound intensity pattern from a loudspeaker

Research question. 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?

C.3 Wave phenomena
SL and HL
Hard data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Sugar concentration and rotation of polarised light

Research question. 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?

C.3 Wave phenomena
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs two polarising sheets, a clear tube, a monochromatic source and a scale; the main uncertainty is locating the intensity minimum by eye.

C.5 Doppler effect: 2 ideas

Frequency shift from a buzzer on a moving trolley

Research question. 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?

C.5 Doppler effect
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Radial velocities of stars from shifted absorption lines

Research question. What radial velocities, in km/s, follow from the shift of the H-α line (656.28 nm) in archive spectra of 10 to 15 stars, and how does the scatter compare with the catalogue values?

C.5 Doppler effect
SL and HL
Needs care
database
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Catalogue radial velocity of each star, 10 to 15 stars covering roughly -100 to +100 km/s, taken from one archive.
What you measure: Observed centre of the H-α line found by fitting a Gaussian in software, giving velocity from v = c(delta λ/lambda0).
Controlled variables: 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.
Physics and graph: Non-relativistic Doppler shift delta λ/lambda0 = v/c. Plot calculated velocity against catalogue velocity, expecting gradient 1 and intercept 0; the residuals show the precision.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Ideas were collected from public lists and published IA titles, merged when they are the same investigation, and rewritten from scratch. “On N sites” counts how many public lists carry the same investigation. How this list was made.

Frequently asked questions

What are good IB Physics IA ideas on waves, wave phenomena and the Doppler effect?

Good starting points with easy data that few sites list are deviation of a ray through a glass prism, focal length and magnification of thin lenses and fringe spacing against screen distance for a laser double slit. Each one gives a straight-line graph from school equipment, which is what the Data analysis and Conclusion criteria need.

Which waves, wave phenomena and the Doppler effect IA ideas are overdone?

refractive index of sugar solutions as a concentration probe and testing malus's law with a rotating analyser and a light sensor appear on three or more public lists. They still work, but they need a twist that shows your own thinking.

Can I do a waves, wave phenomena and the Doppler effect IA at SL?

39 of the 43 ideas use SL physics. The others rely on HL-only content and are marked as HL topics.

IB Physics IA ideas: waves, wave phenomena and the Doppler effect

C.2 Wave model: 8 ideas

C.3 Wave phenomena: 33 ideas

C.5 Doppler effect: 2 ideas

Frequently asked questions

What are good IB Physics IA ideas on waves, wave phenomena and the Doppler effect?

Which waves, wave phenomena and the Doppler effect IA ideas are overdone?

Can I do a waves, wave phenomena and the Doppler effect IA at SL?

Find out what is costing the marks.