Thermal Expansion (Oxford AQA IGCSE Physics)

Thermal Expansion

• When 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

Heating a solid

• When this happens, the space taken up by the substance increases

  • The molecules themselves remain the same size

  • The space in between them increases

Thermal Expansion of Solids, Liquids and Gases

Hazards of thermal expansion

• The expansion of solid materials can cause them to buckle if they get too hot

• This could include:

  • Metal railway tracks

  • Road surfaces

  • Bridges

• Things that are prone to buckling in this way have gaps built in, this creates space for the expansion to happen without causing damage

Useful thermal expansion

• Thermometers rely on the expansion of liquids to measure temperature

• It consists of a thin glass capillary tube containing a liquid that expands with temperature

  • At one end of the tube is a glass bulb, containing a large volume of the liquid which expands into the narrow tube when heated

  • A scale along the side of the tube allows the temperature to be measured based on the length of liquid within the tube

Liquid-in-glass thermometer

• Temperature-activated switches work when a bimetallic strip (a strip made from two types of metal)

• The two metals expand at different rates so the strip bends by a predictable amount at a given temperature

  • When the bimetallic strip is cool, the circuit is not connected

  • When the bimetallic strip is heated, it bends and closes the circuit

Temperature activated switches