IB Physics · exam technique
IB Physics Paper 2: how to structure long-answer questions
On Paper 2, strong students lose marks not because they don't know the physics, but because they answer a different question than the one asked. The fix is mechanical: read the command term, match the answer's shape to it, and show working the examiner can award point by point.
Command terms are the real question
Every IB Physics question is built around a command term that tells you exactly how much to write and in what form. Answer the term, not the topic:
| Command term | What the examiner wants |
|---|---|
| State / Define | One line. No explanation, no working. |
| Determine / Calculate | A number with units — and the working that earns method marks. |
| Describe | What happens, step by step. No "because". |
| Explain | What happens and why — the causal link is the mark. |
| Outline / Suggest | A brief reasoned point; partial credit for a plausible mechanism. |
The most common Paper 2 error: answering "explain" with a "describe". If the question says explain and your answer has no "because / therefore / due to", you've capped your own marks no matter how correct the physics is.
Structure for "determine / calculate"
Numerical parts are scored for method, not just the final number. Lay them out so each mark is visible and a small slip can't cost everything:
- Name the principle — "Using conservation of momentum…".
- Write the relation — the equation in symbols, before numbers.
- Substitute with units — then evaluate.
- State the answer — correct sig-figs, correct unit, sensible magnitude.
This earns the error-carried-forward rule: if you mis-key one number but the method is shown, you still bank the method marks and the answer marks downstream. Students who write only a final number get nothing when it's wrong.
Structure for "explain"
An "explain" answer is a short causal chain. Build it as: observation → physical cause → consequence. For example, "the gas cools (observation) because it does work on the surroundings as it expands (cause), so its internal energy and therefore temperature fall (consequence)." Three linked clauses, three potential marks.
Data and uncertainties — the quiet mark-leak
Paper 2 (and Paper 3) reward correct handling of uncertainty, and it's where many otherwise-strong scripts drop points:
- Quote uncertainties to one significant figure, and match the value's decimal place to it.
- When reading a graph, the gradient carries an uncertainty too — use the steepest/shallowest lines through the error bars.
- Propagate correctly: add absolute uncertainties when adding quantities, add fractional/percentage uncertainties when multiplying or dividing.
Check your numbers fast
Use the free physics calculators to verify a Paper 2 calculation — they show the full working, so you can compare your method line by line.
Paper 2 checklist
- Did I answer the command term, not just the topic?
- For calculations: principle → equation → substitution → answer with units?
- For "explain": is there an explicit because / therefore?
- Sig-figs and units consistent throughout?
- Uncertainties to 1 s.f., propagated the right way?
Want this applied to your own past papers, marked exactly as an examiner would? That's the core of IB Physics tutoring. On the US track instead? See AP Physics and its free-response method. Russian-speaking family abroad — lessons run in English, Russian or both.
Vladimir Podlevskikh — MSU physicist, 23 years teaching physics & maths; IB / AP / A-Level exam preparation. Perfect 200/200 on both US Praxis Physics & Maths.