How to Answer 'Justify' Questions in IGCSE Physics

Use this guide to construct justified answers in Cambridge IGCSE Physics 0625 exams.

What ‘justify’ means

‘Justify’ asks you to provide evidence or reasoning that supports a statement, conclusion or decision. The question may give you the conclusion and ask you to support it, or it may ask you to choose an option and justify your choice.

The justify structure

1. State your conclusion (if the question asks you to choose).
2. Cite the evidence (data, observation or physics principle).
3. Link the evidence to the conclusion (explain how the evidence supports it).

Worked example 1 (2 marks)

Question: The student concludes that the material obeys Hooke’s Law. Justify this conclusion using the data.

Strong answer: “The data shows that doubling the force from 2 N to 4 N doubles the extension from 3 cm to 6 cm. This linear proportional relationship between force and extension is consistent with Hooke’s Law.”

Why it scores: The answer cites specific data points and links the proportional relationship to Hooke’s Law.

Worked example 2 (3 marks)

Question: Suggest which material, A or B, is better for insulating a hot water tank. Justify your answer.

Strong answer: “Material A is the better insulator. The data shows that the water temperature dropped by only 5 degrees C in 30 minutes with material A, compared to 18 degrees C with material B. A smaller temperature drop means less thermal energy was transferred through material A, indicating it is a more effective insulator.”

Common mistakes

• Stating the conclusion without evidence. “Material A is better” with no data earns no marks.
• Citing evidence without linking it to the conclusion. The link is where the mark is.
• Using vague language like “it shows that it works better” instead of specifying what the data says.

Tip

Read the data carefully. Examiners design justify questions so that the data clearly supports one answer. If the data seems ambiguous, look again for the pattern.