AQA GCSE Physics

Revision Notes

1.1.13 Conduction of Heat

Conduction of Heat

  • Conduction is the process of heat (or electricity) being directly transmitted through a material of a substance when there is a temperature difference
    • For example, the heat from a hot cup of coffee also heats up the mug
  • The direction of heat transfer is always from hot to cold
  • The thermal conductivity of a material is a measure of its ability to conduct heat

The higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across the material

  • Materials with high thermal conductivity heat up faster than materials with low thermal conductivity

Materials with high and low thermal conductivity

  • Examples of substances with high thermal conductivity include:
    • Diamond
    • Aluminium
    • Graphite
  • Examples of substances with low thermal conductivity include:
    • Air
    • Steel
    • Bronze

Factors Affecting Conduction

  • An insulator is a substance that doesn’t readily allow heat (or sound) to travel through it
    • Examples include wool, plastic, wood
  • In other words, an insulator is a poor conductor of heat and electricity
  • Insulators are used to contain heat and sound, for example, to keep a house warm or build a soundproof room
    • This is why in cold weather, a woollen jumper is worn to retain body heat and keep warm
  • The energy transfer through a layer of insulating material depends on:
    • The temperature difference across the material – the greater the temperature difference, the more conduction
    • The thickness of the material – it is more difficult for heat to conduct through thicker materials
    • The thermal conductivity of the material – heat conducts better in materials with high thermal conductivity, and vice versa
  • Therefore, good insulators which keep the energy transfer through them as low as possible have:
    • low thermal conductivity
    • Layers that are as thick as possible
  • Insulating the loft of a house lowers its rate of cooling, meaning less heat is lost to the outside
  • The insulation is often made from fibreglass (or glass fibre)
    • This is a reinforced plastic material composed of woven material with glass fibres laid across and held together
    • The air trapped between the fibres makes it a good insulator
  • It has a much lower thermal conductivity than the roof material
  • Several layers of insulation make it very thick and therefore decrease the rate of cooling

 

  • Another aspect that affects the cooling of buildings is the walls
  • Houses in cold countries are fitted with cavity wall insulation which is made from blown mineral fibre filled with gas
    • This lowers the conduction of heat through the walls from the inside to the outside

Less heat is lost from a building with the help of insulation (filled cavity in walls) 

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Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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