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Practice questions · Thermal expansion

Room to grow.

Six original Cambridge-style questions on why heated substances expand, how much each state expands, the engineering it forces, and the common particle misconception.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
The explanation examiners want

More energy, more vibration, more spacing.

01
[2 marks]

Explain, in terms of its particles, why a metal bar gets slightly longer when it is heated.

  • The particles gain energy and vibrate more strongly (with a bigger amplitude). ✓
  • This pushes them slightly further apart, so the average spacing increases and the bar gets longer. ✓
02
[2 marks]

For the same rise in temperature, place a solid, a liquid, and a gas in order of how much they expand, from most to least, and state which one expands the most.

  • Most to least: gas, then liquid, then solid. ✓
  • The gas expands the most. ✓
03
Analysis
[3 marks]

A long steel bridge is built resting on rollers at one end, with a toothed expansion joint in the road surface. Explain why these features are needed.

  • When the temperature rises, the steel bridge expands and becomes longer. ✓
  • The rollers and expansion joint let it lengthen and shorten freely. ✓
  • Without them the forces from expansion could crack or buckle the structure. ✓
04
Analysis
[2 marks]

A bimetallic strip is made of brass joined to iron. Brass expands more than iron for the same temperature rise. Explain what happens to the strip when it is heated.

  • When heated, the brass side expands more than the iron side. ✓
  • The strip bends, curving towards the iron side (the brass forms the outside of the curve). ✓

This bending is used to open and close a switch in a thermostat.

05
Analysis
[2 marks]

A student explains expansion by saying that the particles of the metal grow larger when heated. Explain why this is wrong and give the correct reason.

  • The particles do not change size. ✓
  • They vibrate more and move slightly further apart, so it is the spacing between them that increases, not the particles themselves. ✓
06
Analysis
[2 marks]

A glass jar has a metal lid that is screwed on too tightly to open. Running the lid under hot water makes it easier to unscrew. Explain why, given that metal expands more than glass.

  • The hot water warms the metal lid, which expands more than the glass. ✓
  • The lid becomes slightly larger and looser on the jar, so it is easier to unscrew. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.