Revision Notes

2.2.1 Thermal Expansion

What is Thermal Expansion?

  • When (most) materials are heated, they expand
  • This expansion happens because the molecules start to move around (or vibrate) faster, which causes them to knock into each other and push each other apart

Thermal expansion, IGCSE & GCSE Physics revision notes

When a solid is heated, the molecules vibrate more, pushing each other apart

Note: When this happens, it is the space taken up by the molecules that increases. The molecules themselves remain the same size.


Extended Only

Thermal Expansion in Solids, Liquids & Gases

  • When solids, liquids and gases are heated:

Thermal expansion table, IGCSE & GCSE Physics revision notes


Applications and Consequences

  • The thermal expansion of materials can have some useful applications, but also has some undesirable consequences


  • Applications:
    • The expansion of a liquid in a thermometer can be used to measure temperature
    • A bimetallic strip, consisting of two metals that expand at different rates, can be made to bend at a given temperature, forming a temperature-activated switch

Bimetal thermostat, IGCSE & GCSE Physics revision notes

The bimetallic strip will bend upwards when heated, closing the circuit


  • Consequences:
    • The expansion of solid materials can cause them to buckle if they get too
    • This could include:
      • Metal railway tracks
      • Road surfaces
      • Bridges
    • Things that are prone to buckling in this way often have gaps built into them providing some room for them to expand into


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Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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