Thermal expansion Cambridge IGCSE Physics (9–1) revision
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In plain words
Almost everything gets slightly bigger when it's heated, because its particles move more and push each other further apart. Gases expand most, then liquids, then solids. It's why railway tracks have gaps, and how a liquid-in-glass thermometer works.
Three things to know
- Most substances expand when heated: their particles move more and take up more room. Gases expand most, solids least.
- Expansion is used in liquid-in-glass thermometers and bimetallic strips, and must be allowed for in bridges, railway lines and overhead cables.
- The particles themselves do not get bigger. The spaces between them do.
Tips and tricks
- The particles themselves don't get bigger: they move further apart. Writing "the particles expand" loses the mark.
- Have one example ready of expansion being useful (a thermometer) and one of it being a nuisance (bridges, railway lines, overhead cables).
It lands in your notebook with its questions as flashcards.
Thermal expansion: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Why does a metal bar get longer when heated?
The atoms need more room as they vibrate more.
Which expands most for the same temperature rise?
Gas particles are almost free of each other.
A tight metal lid on a glass jar loosens when held under hot water. Why?
The lid heats up first, and metal expands more than glass.
What is a bimetallic strip used for?
It bends as it heats and can open or close a contact, as in a thermostat.
Why do overhead power cables sag more in summer?
The cables are longer when warm.
What happens to the density of a liquid when it is heated?
The same mass in a bigger volume means a lower density.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
4 questions, 9 marks. Write your answers on paper, then check them.
Thermal expansion
Cambridge IGCSE Physics (9–1) 0972 · 9 marks · papermunch.org
Name ______________________________ Date ______________
Explain why gaps are left between lengths of railway track.[2]
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The rails expand on hot days; without gaps they would push against each other and buckle.
Explain why a liquid-in-glass thermometer has a narrow tube.[2]
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A small expansion of the liquid then moves the level a long way, so small changes in temperature are easy to read.
A bimetallic strip is made of brass and iron. Brass expands more than iron when heated. Describe and explain what happens when the strip is heated.[3]
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It bends, with the brass on the outside of the curve, because the brass becomes longer than the iron.
Explain why a gas expands much more than a solid for the same rise in temperature.[2]
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The forces between gas particles are very weak, so they move apart easily; in a solid, strong forces hold the particles together.
Answers: Thermal expansion
- 1. The rails expand on hot days; without gaps they would push against each other and buckle.
- 2. A small expansion of the liquid then moves the level a long way, so small changes in temperature are easy to read.
- 3. It bends, with the brass on the outside of the curve, because the brass becomes longer than the iron.
- 4. The forces between gas particles are very weak, so they move apart easily; in a solid, strong forces hold the particles together.