How to Answer 'Predict' Questions in IGCSE Physics

Use this guide to handle ‘predict’ questions in Cambridge IGCSE Physics 0625.

What ‘predict’ means

‘Predict’ asks you to use the information given (data, a graph, or a described situation) and your physics knowledge to state what will happen next, or what a value will be.

How to approach predict questions

1. Identify the physics principle that governs the situation.
2. Use the data or pattern to extend the relationship.
3. State your prediction clearly, with a value if possible.

Worked example 1 (2 marks)

Question: A student measures the extension of a spring for loads of 1 N, 2 N and 3 N. The extensions are 2 cm, 4 cm and 6 cm. Predict the extension when the load is 5 N.

Answer: “The extension is proportional to the load (Hooke’s Law). Each 1 N produces 2 cm of extension. For 5 N, the predicted extension is 5 x 2 = 10 cm.”

Worked example 2 (2 marks)

Question: A graph shows that the temperature of water increases steadily from 20 degrees C as it is heated. At 100 degrees C, the temperature stops rising. Predict what happens to the temperature if heating continues.

Answer: “The temperature remains at 100 degrees C because the water is boiling. The energy supplied is used to change the state from liquid to gas (latent heat of vaporisation), not to raise the temperature.”

Worked example 3 (1 mark)

Question: The resistance of a thermistor decreases as temperature increases. Predict what happens to the current through the thermistor as it is heated.

Answer: “The current increases because the resistance decreases (for a constant voltage, I = V/R, so lower R gives higher I).”

Tips

• Look for proportional relationships: if doubling the input doubles the output, extend that pattern.
• State the principle you are using, especially for multi-mark questions.
• If a graph shows a clear trend, extend the line and read off the predicted value.
• Be specific with numbers when the data allows it.