Conduction is the transfer of thermal energy through a material without the material itself moving. It occurs mainly in solids, especially metals.
How conduction works
In all solids, conduction occurs by particle vibration:
- Particles at the hot end vibrate more vigorously.
- They collide with neighbouring particles, transferring kinetic energy.
- Energy passes along the material from particle to particle.
In metals, conduction also occurs by free electron diffusion:
- Metals contain free (delocalised) electrons that can move through the lattice.
- At the hot end, free electrons gain kinetic energy and move faster.
- They diffuse toward the cooler end, colliding with ions and transferring energy.
Free electron conduction is much faster than particle vibration, which is why metals are much better conductors than non-metals.
Conductors and insulators
| Material type | Conduction rate | Reason |
|---|---|---|
| Metals | High (good conductors) | Free electrons transfer energy rapidly |
| Non-metals (glass, wood) | Low (poor conductors / insulators) | No free electrons; only particle vibration |
| Gases | Very low | Particles far apart; few collisions |
| Trapped air (e.g. foam, wool) | Very low | Air is a poor conductor and trapping prevents convection |
Worked example
Explain why a metal spoon in a hot cup of tea feels hot quickly, but a wooden spoon does not.
Metal contains free electrons that rapidly transfer kinetic energy from the hot end (in the tea) to the cool end (your hand). Wood has no free electrons, so energy transfers only by particle vibration, which is much slower.
Common errors and how to correct them
Saying “heat rises through the spoon.” Conduction transfers energy through particle interactions, not by movement of the material. “Heat rises” describes convection, not conduction.
Forgetting to mention free electrons when explaining why metals are good conductors. Both vibration and free electron diffusion occur in metals, but free electrons are the main reason metals conduct so well.
How to apply this in an exam
For a full explanation, describe both mechanisms (particle vibration and free electron diffusion in metals). For non-metals, state that only particle vibration occurs. Always link the mechanism to the rate of conduction.
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