How to Answer 'Explain' Questions in A-Level Physics (9702)

Short answer: An "explain" question in A-Level Physics (9702) wants a cause, not a description. Name the physics principle or equation, then link it clearly to the effect the question asks about. Write one distinct point per mark, use correct terms, and never just restate the question.

Read the command word first

Cambridge questions are built around command words, and each one demands a different type of answer. Mixing them up is the most common way students throw away easy marks.

Command word	What it wants	Typical marks
State	A short fact or value, no working	1
Describe	What happens, in order, no reasons	2 to 4
Explain	The reason why, using physics	2 to 4
Suggest	An applied idea in a new context	1 to 3
Show that	Working that leads to a given value	2 to 3

If the word is explain, the examiner has already told you they want a mechanism. A description of what happens will not score the reasoning marks.

The cause and effect rule

Every good explain answer connects a cause to an effect through a named piece of physics. A reliable structure is:

1. State the relevant principle or equation.
2. Say what changes (the cause).
3. Say what that change produces (the effect).

For example, if asked to explain why a metal wire extends more when the load increases, a strong answer says: the extension is proportional to the applied force within the limit of proportionality (Hooke's law, $F = kx$), so doubling the force doubles the extension. That names the law, the cause, and the effect in one chain.

One point per mark

Examiners mark explain questions point by point against the mark scheme. A 3 mark question needs three separate, creditable statements. Writing a single flowing paragraph that says the same thing three ways scores one mark, not three.

A quick self-check: after writing your answer, count the distinct physics ideas. If a 3 mark question has fewer than three, you are almost certainly missing marks.

Use the right vocabulary

The mark scheme rewards precise terms. Vague words lose marks even when the idea is roughly right.

Vague phrasing	Precise phrasing
The force pushes the electrons	The potential difference does work on the charge carriers
It speeds up	The resultant force produces an acceleration
The energy is lost	Energy is transferred to the surroundings as heat
It gets bigger	The quantity increases in proportion to...

A worked example of technique

Question style: "Explain why a body moving in a circle at constant speed is accelerating." (2 marks)

Weak answer: "It is accelerating because it is moving in a circle." This just restates the question and scores zero.

Strong answer: "The direction of the velocity is continuously changing, and since velocity is a vector, a change in direction is a change in velocity. A changing velocity means there is an acceleration, directed towards the centre of the circle." That is two clear points: velocity changes direction, therefore there is acceleration. Both marks secured.

Notice there is no calculation. The relationship $a = \frac{v^2}{r}$ could be mentioned, but the marks here are for reasoning about vectors, not arithmetic.

Common traps in 9702 explain questions

• Restating the question. If the answer could have been written without knowing any physics, it scores nothing.
• Describing when asked to explain. Listing the steps of what happens misses the "why".
• Contradicting yourself. Examiners cannot award a mark if a correct statement sits next to a wrong one that cancels it out.
• Running out of distinct points. Padding a short answer with repetition wastes time and gains nothing.

A quick checklist before you move on

• Did I name a principle, law, or equation?
• Did I link a cause to an effect?
• Do I have at least one distinct point per mark?
• Did I use precise physics terms, not everyday words?

Get those four right and explain questions become some of the most predictable marks on the paper.

If you want to test your answers, ExamPal is an AI tutor that already knows the 9702 syllabus and marks your written explanations against the Cambridge mark scheme, so you can see exactly which reasoning marks you would have picked up.