IGCSE Physics Command Words Decoded

Most lost marks in IGCSE Physics 0625 are not physics errors. They are command word errors. A student who knows the content perfectly can still describe when the question says explain, or estimate when it says calculate. Cambridge publishes exact definitions for each command word, and examiners mark against them. Learn the seven below and you stop donating marks.

What do command words actually mean in IGCSE Physics?

A command word tells you the type of answer the examiner can credit. State wants a fact. Calculate wants working and a number with a unit. Explain wants a cause linked to an effect. Match your answer type to the command word and the mark scheme opens up.

Here is the quick-reference table. The sections below decode each one with a model answer fragment.

State

State means write the fact and stop. One mark, one fact. No working, no justification.

Question fragment: State the unit of momentum.

Model fragment: “kg m/s.” That is the whole answer. Students who add a sentence of context waste 30 seconds and risk contradicting themselves. Examiners apply a “contradiction cancels credit” rule. A correct fact followed by a wrong one scores zero.

If a state question carries two marks, give two separate facts. State two factors that affect the resistance of a wire needs “length” and “cross-sectional area” as distinct points.

Describe

Describe means say what happens, usually in order, without giving the reason.

Question fragment: Describe the motion shown between 4 s and 10 s on the speed-time graph.

Model fragment: “The object decelerates from 12 m/s, at a constant rate, reaching 0 m/s at 10 s.” Three observable features: what the speed does, how it changes, and the values. No mention of forces, because the question did not ask why.

For experiments, describe means list the steps a competent student could follow. Use numbered steps, name the measuring instruments, and say what you would record.

Explain

Explain means give the physics reason. Every explain answer needs a cause linked to an effect, usually with “because” or “so”.

Question fragment: Explain why the pressure of a gas increases when it is heated at constant volume.

Model fragment: “Heating increases the average kinetic energy of the molecules, so they move faster. They collide with the container walls more frequently and with greater force, so the pressure increases.” Notice the chain: heat → faster molecules → harder, more frequent collisions → higher pressure. Mark schemes credit each link separately, B1 style. Miss a link and you lose that mark.

The classic failure: writing “the molecules have more energy” and stopping. That describes the cause but never connects it to pressure.

Calculate

Calculate means produce a numerical answer with working and a unit. Mark schemes split these as M1 for the method and A1 for the answer.

Question fragment: Calculate the weight of a 6.0 kg mass. ($g = 9.8\ \text{N/kg}$)

Model fragment: ”$W = mg = 6.0 \times 9.8 = 58.8\ \text{N} \approx 59\ \text{N}$.”

Write the equation, substitute, then evaluate. Even with a wrong final answer, the substituted equation usually earns the M1 mark. Note that 0625 standardises on $g = 9.8\ \text{N/kg}$, but some papers use $10\ \text{N/kg}$, so read the value given in the question and use it.

Give answers to two or three significant figures unless told otherwise, and never drop the unit. A missing unit on the answer line costs the A1 mark on many questions.

Determine

Determine means the value cannot come straight from one substitution. You must extract data first: read a graph gradient, take an intercept, or combine two equations.

Question fragment: Determine the acceleration of the car from the graph.

Model fragment: ”$\text{Gradient} = \dfrac{20 - 8}{6 - 2} = \dfrac{12}{4} = 3.0\ \text{m/s}^2$.” Quote the coordinates you read, show the division, state the unit. Examiners want to see a large gradient triangle, spanning at least half the line, because small triangles magnify reading errors.

In Paper 6, determine often means process your recorded results. For example, determine the average time for one oscillation by dividing the time for 20 swings by 20.

Suggest

Suggest signals an unfamiliar context. There is no single right answer; examiners credit any physically sound response.

Question fragment: Suggest why the measured value of g in the experiment is lower than $9.8\ \text{N/kg}$.

Model fragment: “Air resistance acts on the falling object, so its acceleration is less than the acceleration of free fall.” Any sensible mechanism scores: friction at the pulley, reaction-time error starting the timer late, and so on. Apply known physics to the new situation rather than hunting for a memorised answer.

Students fear suggest questions most, yet they are often the most generously marked. In our 1-to-1 classes, tutors drill suggest questions from past papers until students treat them as free marks rather than traps.

Show that

Show that hands you the destination and pays you for the journey.

Question fragment: Show that the kinetic energy of the ball is about 45 J. (mass 0.40 kg, speed 15 m/s)

Model fragment: ”$E_k = \dfrac{1}{2}mv^2 = 0.5 \times 0.40 \times 15^2 = 0.5 \times 0.40 \times 225 = 45\ \text{J}$.” Every step appears. Because the answer is given, the marks sit entirely in the working. Skipping the substitution line scores zero even though your “answer” is correct.

Work to one more significant figure than the quoted value, then round. If the question says “about 45 J” and you get 45.0 J, state it. A follow-on part often uses this value, so a show-that question also protects you: even if you failed to show it, use the given 45 J in the next part and you still score there.

How should you practise command words?

Take one past paper and highlight every command word before answering anything. Then check each of your answers against the type it demanded: fact, sequence, cause, or working. Most students find that 8 to 12 marks per paper were lost to mismatched answer types, not missing knowledge. Repeat this audit on three papers and the habit sticks.

A second drill: rewrite one describe answer as an explain answer, and one explain as a describe. The contrast trains you to feel the difference. This is exactly the marking-aware practice our handpicked Physics specialists run in 1.5-hour online classes. Students mark their own answers against real scheme language until command words become automatic. The free trial lesson usually starts here, because it produces the fastest visible mark gain.

Command words are the cheapest marks on the paper to recover. Learn the seven definitions, audit three past papers, and your score rises before you revise a single extra topic.