Section 1 of 5How Conduction Works
1
Particles at the hot end of a solid gain kinetic energy and vibrate more strongly than particles at the cool end.
2
The vibrating particles pass energy on to neighbouring particles by colliding with them, moving energy along the solid.
3
Energy always flows from the hotter region to the cooler region until thermal equilibrium is reached.
4
Conduction happens in metals and non-metals alike, but in metals the free electrons speed up the transfer considerably.
Section 2 of 5Conductors and Insulators
Metals
- Metals are the best thermal conductors because their free electrons carry energy quickly through the structure.
Liquids
- Liquids conduct poorly, but better than gases, because their close particles can pass vibrations along.
Gases
- Gases are poor conductors because their particles are widely spaced and collide only rarely.
Insulators
- Materials such as wool, plastic, wood and rubber conduct poorly, so they reduce energy transfer through them.
Section 3 of 5Reducing Conduction
Reducing Conduction
Trapped air
- Air is a poor thermal conductor, so air trapped in a jumper or a foam layer slows energy transfer.
Thickness
- A thicker layer of insulation gives a lower rate of energy transfer, because energy has further to travel.
Vacuum flask
- A vacuum between two walls removes the particles needed for conduction, which slows heat loss from a drink.
Low conductivity
- Materials with low thermal conductivity are chosen as insulators because they transfer little energy per second.
Section 4 of 5Comparing Conduction
Materials are compared by how easily they pass energy along through their particles.
Comparing Conduction
Metal versus liquid
- Metals conduct much better than liquids,
- because free electrons carry energy quickly while liquid particles pass vibrations along slowly.
Liquid versus gas
- Liquids conduct better than gases, because their particles are closer together and collide more often.
Non-metal solids
- Non-metal solids such as glass still conduct by vibration, but they conduct far less well than metals do.
Air gaps
- Double glazing traps a layer of air between two panes of glass, which reduces the energy lost by conduction through a window.
Section 5 of 5Exam Checklist & Tips
4.2.1 – Key Points for the Exam
- Thermal conduction Energy transfer through a substance by vibrating particles and free electrons.
- Free electrons Electrons in a metal that are free to move through the structure and carry energy.
- Thermal conductor A material that transfers energy quickly by conduction.
- Insulator A material that is a poor thermal conductor.
- Thermal equilibrium The state reached when two parts of a system are at the same temperature.
- Thermal conductivity A measure of how well a material conducts thermal energy.
Common Mistakes
- Saying that particles travel through the material during conduction;
- they vibrate and pass energy on while staying in place.
- Explaining insulation by saying the object warms the insulator, which warms the object again;
- the insulator traps air that conducts poorly.
- Claiming that conduction moves energy from cold to hot.
- Saying gases conduct better than solids because their particles move faster.