Pietro MeloniPhD

34 ideas · B.5 · 2025 syllabus

IB Physics IA ideas: current and circuits

Circuit investigations are the most reliable IAs to get data from: resistance, resistivity, internal resistance, thermistors and LEDs, all measured with a multimeter. Because the data is clean, the marks go to design and to the uncertainty analysis.

By Pietro Meloni, PhD · Updated on 26 September 2026

34 of 34 ideas

B.5 Current and circuits: 34 ideas

Temperature coefficient of resistance of a metal wire

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Overdone: on 4 sites

My take. 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.

Method, physics and where marks are lost+

Independent variable: Bath temperature, 20 to 90 °C in 10 °C steps (8 values), each repeated 3 times on both heating and cooling.
What you measure: 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).
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Cold and warm effects on a AA cell's internal resistance

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Common: on 3 sites

My take. 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.

Method, physics and where marks are lost+

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

Current voltage curves of a solar cell at varied irradiance

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Common: on 3 sites

My take. 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.

Method, physics and where marks are lost+

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

Forward voltage drop of a diode against temperature

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Common: on 2 sites

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Multimeter, resistor and water bath are enough; the main uncertainty is that the thermometer and diode may not be at the same temperature.

NTC thermistor Beta parameter from a water bath

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Common: on 2 sites

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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).
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a thermistor, beaker, kettle, ice, thermometer or temperature probe and a multimeter; main uncertainty is thermal lag between probe and thermistor.

Resistance of nichrome wire against length

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Common: on 2 sites

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: Potential difference by voltmeter and current by ammeter, then R = V/I. Use low current, kept below 0.5 A.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: Research design: heating changing the resistance. Data analysis: ignoring the diameter uncertainty in ρ. Evaluation: clip contact resistance shown by the non-zero intercept.
Data: Standard kit with a power supply, meters and micrometer; the main uncertainty is diameter and contact resistance.

Time constant of a discharging capacitor against resistance

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Common: on 2 sites

My take. 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.

Method, physics and where marks are lost+

Independent variable: Resistance, 10, 20, 30, 40, 50, 60, 80 and 100 kΩ, using 1% resistors checked with a multimeter. Three discharges per value.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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%.
SL and HL: 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.
Where marks are lost: 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.
Data: A capacitor, resistors, a power supply and a logger or a phone video; the main uncertainty is capacitor tolerance and meter loading.

Capacitor charging voltage against energy released

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Rarely listed

My take. Only worth it if energy is measured rather than calculated. The lifted mass method gives you real data to defend.

Method, physics and where marks are lost+

Independent variable: Charging voltage, 2 to 12 V in six steps, 5 repeats each, set from a variable power supply and confirmed with a voltmeter.
What you measure: 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.
Controlled variables: Same capacitor, discharged fully between runs; same motor and load mass; same wiring and connection resistance; same room temperature.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a capacitor, supply, voltmeter and small motor; the main uncertainty is the capacitor tolerance and energy lost in the motor.

Cell temperature and open-circuit voltage of a solar cell

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a solar cell, multimeter, thermometer and a heat source; the main uncertainty is thermal lag, so wait for readings to settle.

Discharge curves for capacitors in series and parallel

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Rarely listed

My take. Fine and easy, if you focus on time constant rather than vague voltage. Measure each capacitor first to keep the data honest.

Method, physics and where marks are lost+

Independent variable: Number of identical capacitors in series, 1 to 5; five values, with 3 to 5 discharge runs each.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs capacitors, resistor and a logger; the main uncertainty is capacitor tolerance and the voltmeter loading the circuit.

Efficiency of a small DC motor lifting a load

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Lifted mass from 20 g to 120 g, 6 values, each with 3 repeats.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Filament lamp I-V curve at different starting conditions

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

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

Finding emf and internal resistance of a AA cell

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a cell holder, resistor set or decade box, two multimeters; main uncertainty is cell drift and the small voltage differences at high R.

Internal resistance of a 4.5 V battery from load tests

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Load resistance from a decade box or set of resistors, 5, 10, 15, 22, 33, 47, 68 and 100 Ω, each measured twice.
What you measure: Terminal voltage with a digital voltmeter and current with an ammeter. Internal resistance found from the gradient of V against I.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Basic circuit kit only; main uncertainty is the battery drifting, which the open circuit check exposes.

Internal resistance of a cell as it discharges

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: An AA cell, variable resistor and two meters are enough; the main uncertainty is contact resistance and the cell recovering between readings.

Internal resistance of cells from a load-current sweep

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Rarely listed

My take. Routine, but reliable if done well. The discharge-over-time part is the twist that lifts it above the standard version.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a cell, holder, resistor box or fixed resistors and two meters; the main uncertainty is drift from discharge and contact resistance.

LED brightness against forward current for three colours

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a lux meter or light sensor plus a variable supply; the main uncertainty is sensor alignment and its colour-dependent response.

Layers of cellophane and solar panel power output

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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).
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a solar panel, lamp, two multimeters and cellophane; the main uncertainty is lamp output drifting as it warms, so warm it up first.

Light dependent resistor response to varying illuminance

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

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

Pitch angle of model turbine blades and power delivered

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Blade pitch angle, 7 values from 0 to 60 degrees, set with a protractor jig or printed template. Three runs per angle.
What you measure: Voltage across a fixed load resistor with a multimeter or logger; power P = V²/R. Air speed at the turbine measured with an anemometer.
Controlled variables: 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.
Physics and graph: Power available in wind is P = 1/2 ρ A v³, 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 v³, gradient linked to efficiency.
SL and HL: SL students find the optimum angle and give an efficiency. Higher marks come from checking the v³ dependence, explaining why power drops at large angle (stall, less swept effect) and quantifying the air speed non-uniformity of a fan.
Where marks are lost: 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.
Data: 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.

Power transfer efficiency against load resistance

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Rarely listed

My take. Neat and cheap, with a memorable peak. The best twist is the comparison of the three ways to obtain internal resistance.

Method, physics and where marks are lost+

Independent variable: Load resistance R, values of 2, 5, 10, 15, 22, 33, 68 and 100 Ω, from a decade box, two runs each.
What you measure: Terminal voltage and current with two multimeters. Load power = VI, efficiency = V/ε, where ε is the open circuit emf measured first.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: Research design: efficiency never defined properly. Data analysis: no propagation into the peak position. Evaluation: overlooking battery drain and resistor heating.
Data: Simple circuit kit; small uncertainty in resistances, but battery drift needs the emf check.

RC circuit as a model of a nerve membrane

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Resistance R: 10, 22, 33, 47, 68 and 100 kΩ (6 values), with 3 discharge runs for each.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: 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.

Resistance and heating of nichrome wires of different diameter

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Wire diameter measured with a micrometer at several points, six gauges from 0.20 to 0.71 mm, three separate pieces each where possible.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a power supply, micrometer, meters and a thermometer; the diameter uncertainty and heat loss to the surroundings dominate.

Resistance by ammeter-voltmeter versus ohmmeter across a range

Research question. 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)?

B.5 Current and circuits
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a power supply, two multimeters and a resistor set; the main uncertainty is meter resolution and lead resistance at the low end.

Resistance of a constantan wire against its length

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: Potential difference across the wire (digital multimeter, V) and current (ammeter, A); resistance R = V/I calculated for each length.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a constantan or nichrome wire, a power supply, two meters and a micrometer; the main uncertainty is the diameter and the clip contact.

Resistance of copper coil and Peltier against temperature

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Temperature of a water bath: 30, 40, 50, 60, 70 and 80 °C, with two readings on heating and two on cooling.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: Research design: not sealing samples, or temperature lag between bath and sample. Data analysis: no fit uncertainty. Evaluation: heating and cooling hysteresis ignored.
Data: Needs a hot water bath, a sealed sample and a precise meter; copper resistance changes are small, so lead resistance matters.

Resistance of pencil leads with different hardness grades

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a micrometer and a low resistance measurement setup; contact resistance at crocodile clips is the main uncertainty.

Resistance of saltwater against salt mass

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: A beaker, electrodes, a low voltage AC supply or signal generator and two meters; polarisation with DC is the main trap.

Resistivity of a wire from its V-I gradient

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: R = ρ L / A and V = IR. Plot V against I for each length to get R, then plot R against L; the gradient equals ρ / A, so ρ = gradient times A.
SL and HL: SL students get R from the gradient and then ρ. 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.
Where marks are lost: 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.
Data: Power supply, rheostat, two meters, metre rule and micrometer; the main uncertainty is the wire diameter and contact resistance.

Resistivity of metals compared by wire length method

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Rarely listed

My take. Sound and manageable. Very common with a single wire, so the comparison across four metals and an intercept discussion make it worth choosing.

Method, physics and where marks are lost+

Independent variable: Wire length, five values from 0.20 m to 1.00 m for each of the four materials, with material as a second comparison.
What you measure: 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.
Controlled variables: 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.
Physics and graph: R = ρL/A. Plot R against L; the gradient is ρ/A, so ρ = gradient × A. The conductivity is σ = 1/ρ.
SL and HL: 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.
Where marks are lost: 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.
Data: Wire reels, micrometer and meters from a school kit; the diameter uncertainty is the largest contribution to error in ρ.

Solar cell output against lamp distance

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Distance from lamp to cell: 10, 15, 20, 30, 40, 50, 60 cm (7 values), 3 repeats each, measured along a metre rule.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Needs a lamp, a small solar cell, two multimeters and a rule; the main uncertainty is the true source position and stray light.

Testing Ohm's law for a resistor and a filament lamp

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Rarely listed

My take. Only worth doing with the lamp or another non-ohmic part included, otherwise it is too basic. Estimating filament temperature makes it your own.

Method, physics and where marks are lost+

Independent variable: 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.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Only a power supply, two multimeters, a resistor and a lamp are needed; the main uncertainty is meter resolution and self-heating.

Testing Ohm's law on a resistor and a filament lamp

Research question. 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?

B.5 Current and circuits
SL and HL
Easy data
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Potential difference from 0.5 V to 6.0 V, 12 values, set with a variable power supply or a potentiometer arrangement.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: 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.
Where marks are lost: 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.
Data: Standard school kit; main uncertainty is resistor heating and the meter's last-digit resolution.

Time constant of a discharging capacitor across five capacitances

Research question. 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?

B.5 Current and circuits
SL and HL
Needs care
Rarely listed

My take. 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.

Method, physics and where marks are lost+

Independent variable: Capacitance C, 5 to 6 values from 100 to 1000 microfarad (using single capacitors or parallel combinations), each discharge repeated 3 times.
What you measure: 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.
Controlled variables: 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.
Physics and graph: 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.
SL and HL: SL students can do the τ against C graph and compare gradient with the resistor value. Stronger work explains why the multimeter's own resistance reduces τ and handles capacitor tolerance (often 20 percent) by measuring C directly. HL students can link to exponential decay and energy stored.
Where marks are lost: 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.
Data: Needs electrolytic capacitors, resistor, power supply and a logger or video timing; main uncertainty is capacitor tolerance and meter loading.

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 current and circuits?

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Good starting points with easy data that few sites list are capacitor charging voltage against energy released, filament lamp i-v curve at different starting conditions and finding emf and internal resistance of a aa cell. Each one gives a straight-line graph from school equipment, which is what the Data analysis and Conclusion criteria need.

Which current and circuits IA ideas are overdone?

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temperature coefficient of resistance of a metal wire, cold and warm effects on a aa cell's internal resistance and current voltage curves of a solar cell at varied irradiance appear on three or more public lists. They still work, but they need a twist that shows your own thinking.

Can I do a current and circuits IA at SL?

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Yes. All 34 ideas on this page use physics from the SL syllabus. HL students can take the same ideas further, and each idea says how.

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