QCE Physics IA2 experiment design and report writing: The 2026 guide

What this guide is for

The QCE Physics IA2 is the Student Experiment, worth 20 percent of the subject result. It is a student-designed and student-conducted Unit 3 experiment, reported as a 1500 to 2000-word scientific report. The published companion guide on this site covers report structure and common contexts. This guide is the design and writing playbook: how to choose a research question, justify the methodology, propagate uncertainty, linearise, and write a discussion that hits every QCAA criterion.

The IA2 is graded against published QCAA criteria covering research and planning, analysis of evidence, interpretation and evaluation, and conclusion. Top band requires evidence of excellence in all four.

Choosing the research question

A good IA2 research question is narrow, controllable and tied to one Unit 3 equation. Three tests.

First. The underlying theoretical relationship is one named equation, not a chain. Pendulum period from length is one equation ($T = 2\pi\sqrt{L/g}$). Range of a projectile from launch angle is one equation ($R = v^2 \sin(2\theta)/g$). Transformer voltage ratio from turns ratio is one equation ($V_s/V_p = N_s/N_p$). All three are tractable.

Second. The IV is controllable to at least five distinct values within laboratory time. Pendulum length from 0.25 m to 1.25 m in 0.25 m increments is straightforward. Projectile launch angle from 15 to 75 degrees in 10-degree increments is straightforward, assuming a fixed-velocity launcher.

Third. The DV is measurable to better than 5 percent precision with school instruments. A period of 1.0 s measured with a stopwatch carries about 0.2 s reaction time uncertainty, so a single trial gives 20 percent uncertainty. Three trials drop this to about 12 percent. Photogates drop it to under 1 percent. The choice of instrument is part of the design.

A weak research question fails one of these tests. "How does air resistance affect a falling object" fails the first test (no single Unit 3 equation governs it). "How does temperature affect electrical resistance" fails the syllabus mapping (this is not Unit 3). "How does the launch velocity of a marble affect range" fails the third test at most schools, because the launch velocity is hard to measure accurately.

Justifying the methodology

The QCAA research-and-planning criterion rewards explicit justification of design choices. Every choice gets a sentence.

Why these IV values. "Five values from 0.25 m to 1.25 m were chosen to span a factor of five in length, giving a clear gradient on the linearised graph while staying within the school pendulum stand's vertical clearance of 1.5 m."

Why this many trials. "Three trials per IV value were conducted, with the mean reported and the half-range used as the random uncertainty. This is sufficient for stopwatch-precision data; a fourth trial would not meaningfully reduce uncertainty."

Why these controlled variables. "The bob mass was held at 50.0 plus/minus 0.1 g across all trials, because $T = 2\pi\sqrt{L/g}$ predicts no mass dependence; varying mass would test that prediction and was beyond the scope of this question."

Why this instrument. "Period was measured with a stopwatch (resolution 0.01 s, reaction time approximately 0.2 s). A photogate would have given better precision but was not available; the trade-off was managed by timing ten oscillations and dividing by ten."

The marker is looking for evidence that you made these choices deliberately, not by accident.

Data collection and uncertainty

Raw data goes in a table with units in the column headers. Every measured value carries its absolute uncertainty (from the instrument resolution and, where relevant, reaction-time or parallax estimates).

Processed data goes in a second table. Means, derived quantities, propagated uncertainties.

For sums and differences. Add absolute uncertainties.

For products and quotients. Add fractional uncertainties, then convert back to absolute.

For powers. Multiply the fractional uncertainty by the power. For $T^2$ where $T$ has 5 percent uncertainty, $T^2$ has 10 percent uncertainty.

For means. The half-range across trials is the practical uncertainty estimator at IA2 level. Standard deviation is acceptable but the half-range is what most QCAA exemplars use.

Linearisation

Most Unit 3 relationships are non-linear. Linearisation transforms them so that a straight-line graph extracts a physically meaningful gradient.

Pendulum. $T = 2\pi\sqrt{L/g}$ becomes $T^2 = (4\pi^2/g) L$. Plot $T^2$ (vertical) against $L$ (horizontal). The gradient is $4\pi^2/g$, so $g = 4\pi^2 / \text{gradient}$.

Projectile range. $R = v^2 \sin(2\theta)/g$ becomes $R = (v^2/g) \sin(2\theta)$. Plot $R$ against $\sin(2\theta)$. The gradient is $v^2/g$.

Induced EMF. For a magnet moving at speed $v$ through a coil, $\varepsilon \propto v$ at fixed geometry. Plot $\varepsilon$ against $v$ directly; the relationship is already linear.

Draw the best-fit line by eye, then the steepest and shallowest lines that still pass through every error bar. Half the difference in their slopes is the gradient uncertainty.

The discussion

Band 6 discussions are specific. For every uncertainty source, name the experimental step, quantify the contribution if possible, and propose a specific improvement.

Generic. "Parallax error may have affected the readings."

Specific. "Parallax error in reading the protractor scale to set the launch angle contributed up to approximately 2 degrees of uncertainty at high angles, which propagates to about 8 percent uncertainty in $\sin(2\theta)$ near 75 degrees. A digital inclinometer would resolve this to better than 0.5 degree."

Generic. "Air resistance was not accounted for."

Specific. "Air resistance on the marble (drag coefficient approximately 0.4, mass 5 g, peak velocity 5 m/s) is estimated as about 1 percent of the gravitational force, so its effect on the trajectory is within the experimental uncertainty bars and does not affect the conclusion."

The discussion also addresses limitations of the experimental design (range, scope, controlled variables that were assumed but not tested) and proposes improvements.

The conclusion

A direct answer to the research question. State the experimental value with its uncertainty. Compare to theoretical or accepted value. State whether the hypothesis is supported within experimental uncertainty.

"The measured value of $g$ was 9.7 plus/minus 0.4 m/s$^2$, which agrees with the accepted value of 9.81 m/s$^2$ to within experimental uncertainty. The hypothesis is supported."

Check your knowledge

Six student-experiment process questions for IA2. These rehearse the moves a marker rewards across research-question design, methodology justification, uncertainty propagation, and evaluation. ISMG criteria are signposted in the solutions. Three significant figures, units throughout.

1. A student proposes the research question "How does mass affect the period of a pendulum?" Identify three flaws against IA2 top-band specificity and rewrite the question to address each, naming a single Unit 3 equation. (4 marks)
2. A projectile-range experiment uses a spring-loaded launcher firing a 20 g steel ball at fixed initial speed onto a marked floor at five launch angles (15, 30, 45, 60, 75 degrees, $\pm$ 0.5 degrees). List five controlled variables the student must hold constant and for each justify why with reference to the projectile range equation $R = u^2 \sin(2 \theta)/g$. (5 marks)
3. The student measures induced EMF $\varepsilon$ as a function of magnet drop speed $v$ through a coil. Five paired values: 0.50 m s$^{-1}$ $\rightarrow$ 0.10 V; 1.00 $\rightarrow$ 0.21 V; 1.50 $\rightarrow$ 0.30 V; 2.00 $\rightarrow$ 0.42 V; 2.50 $\rightarrow$ 0.51 V. Voltage read-off uncertainty is $\pm$ 0.01 V and speed uncertainty is $\pm$ 0.05 m s$^{-1}$. (a) State the theoretical relationship and predict the gradient given a coil constant of $N A B / L = 0.20 \ \text{V s m}^{-1}$. (b) Calculate the gradient using the first and last data points with min/max line method, reporting uncertainty. (c) Compare with prediction and identify the dominant uncertainty source. (7 marks)
4. The student's evaluation reads: "The major source of error was human error in timing." Identify three weaknesses in this evaluation, and rewrite a one-paragraph evaluation that addresses all three for a pendulum experiment measuring $g$. (5 marks)
5. A linearisation is required to test $T = 2\pi \sqrt{m/k}$ for a vertical mass-spring oscillator at five masses. Five paired values: $m$ (kg): 0.100, 0.200, 0.300, 0.400, 0.500; $T$ (s): 0.50, 0.71, 0.87, 1.00, 1.12. (a) Linearise the equation and state what should be plotted on each axis. (b) Calculate the gradient using the first and last linearised points, and from it determine $k$. (c) Identify one source of systematic error that would shift the apparent $k$ from its true value. (6 marks)
6. A transformer ratio experiment measures $V_s/V_p$ at five turns ratios $N_s/N_p$: 0.10, 0.25, 0.50, 1.00, 2.00; observed $V_s/V_p$: 0.094, 0.236, 0.475, 0.948, 1.892. (a) Calculate the percent deviation of each point from the ideal-transformer prediction $V_s/V_p = N_s/N_p$. (b) State the pattern in the deviations. (c) Propose a physical explanation, identify the dominant non-ideal effect, and suggest one modification to reduce it. (6 marks)