Section 1 of 8How conduction works
1Hot end
- Hot end Particles at the hot end have more kinetic energy and vibrate more strongly.
2Collisions
- Collisions They jostle their neighbours, passing energy to the kinetic stores of the next particles.
3Energy passes along
- Energy passes along The vibration spreads through the material, always from hot to cold.
4Cold end warms
- Cold end warms The thermal store at the cold end increases until the temperatures even out.
Section 2 of 8Conductors and insulators
| Property | High thermal conductivity | Low thermal conductivity |
|---|---|---|
| Rate of energy transfer | Fast | Slow |
| Examples | Aluminium, copper, diamond, graphite | Air, wood, glass, wool, plastic |
| Uses | Saucepans, radiators, heat sinks | Oven gloves, clothing, house insulation |
| Why | Metals have free electrons that carry energy quickly through the structure | Particles are far apart or tightly bound, with no free electrons |
Section 3 of 8What controls the rate of transfer?
Rate of conduction through a layer
Temperature difference
- Temperature difference The bigger the difference between the two sides, the faster the energy transfer.
Thickness
- Thickness A thicker layer slows the transfer because energy has further to travel.
Thermal conductivity
- Thermal conductivity A higher conductivity means a higher rate of transfer.
Best insulator
- Best insulator Low thermal conductivity and as thick as practical.
Section 4 of 8Insulating a home
Loft insulation
- Loft insulation Fibreglass is woven plastic-reinforced glass fibre.
- The air trapped between the fibres is a poor conductor, so it greatly lowers the rate of energy loss through the roof.
Thickness matters
- Thickness matters Several layers make the insulation thick, reducing energy lost to the outside further.
Clothing
- Clothing A woollen jumper traps air, slowing the loss of body heat.
Section 5 of 8Comparing conductors in an experiment
1
Fix rods of equal length and thickness but different materials (e.g. copper, aluminium, steel, glass) so that one end of each can be heated by the same Bunsen flame or hot water.
2
Attach a small drawing pin to each rod with a blob of wax, at equal distances from the heated end.
3
Heat all the rods at the same time, using the same heat source, and start a stopwatch.
4
Record the time taken for each pin to fall as the wax melts. The shorter the time, the better the conductor.
5
Keep the control variables (length, diameter, heating method, starting temperature) the same, and take care with the hot apparatus and flame.
Section 6 of 8Why metals conduct best
| Material type | Method of energy transfer | Result |
|---|---|---|
| Metal | Vibrating ions pass on energy, and free (delocalised) electrons move and collide with other particles carrying energy rapidly | Very good conductor |
| Non-metal solid (e.g. glass, wood) | Only vibrations passed between neighbouring particles | Poor conductor |
| Gas (e.g. air) | Particles far apart, so collisions are rare | Very poor conductor, which is why trapped air is a good insulator |
Section 7 of 8Key terms
| Term | Meaning |
|---|---|
| Conduction | Transfer of energy through a material by vibrating particles passing energy to their neighbours. |
| Thermal conductivity | A measure of how well a material transfers energy by conduction. |
| Insulator | A material with low thermal conductivity. |
| Temperature difference | The difference between the temperatures of two regions. |
| Free electrons | Electrons in a metal that can move through the structure and carry energy. |
| Rate of energy transfer | The amount of energy transferred each second through a material. |
Section 8 of 8Exam technique
1
Saying that cold flows into a warm object. Energy always moves from hot to cold.
2
Claiming particles themselves travel along the rod in conduction. They vibrate in place and pass on energy.
3
Forgetting that a thicker layer of insulation reduces the rate of energy transfer.
4
Saying air is a good insulator because it has 'no particles'. Its particles are far apart so collisions are rare.
5
Confusing a material feeling cold with it being at a lower temperature. A metal feels colder because it conducts energy away from the hand faster.