1.10 - Conduction, Convection & Radiation

Conduction transfers energy through vibrating particles

• Conduction is the way energy spreads through a material when its particles pass energy from one to the next.
• It's the main way energy is transferred by heating through solids.

How it works

1. Heating one part of an object transfers energy to the kinetic energy stores of its particles, so the particles in the heated part vibrate faster.
2. As they vibrate, they collide with their neighbours and pass some energy on. Those particles then vibrate faster too.
3. The process carries on through the object until energy has spread to the other side, raising its temperature.

Good and bad conductors

• Thermal conductivity describes how quickly a material transfers energy this way.
• A material with high thermal conductivity transfers energy quickly and is a good thermal conductor (such as metals).
• A material with low thermal conductivity transfers energy slowly and is called a thermal insulator (such as gases, most liquids, plastic, and wood).

Convection transfers energy by moving particles

• Convection is the way energy is carried through a liquid or a gas by the movement of the particles themselves.
• It can't happen in solids, because the particles are fixed in place and can only vibrate.

Why heated regions rise

1. When a region of a liquid or gas is heated, its particles gain energy and move faster, spreading further apart.
2. This makes the heated region expand and become less dense than the cooler material around it.
3. The warmer, less dense region rises, and the cooler, denser material sinks to take its place.

How a convection current forms

With a constant heat source, this sets up a circulation called a convection current:

1. Material above the heat source warms, becomes less dense and rises.
2. Cooler, denser material flows in below to replace it.
3. The risen material cools, becomes denser again and sinks.
4. The cycle repeats, circulating energy through the whole liquid or gas.

Radiation transfers energy without particles

• Conduction and convection both need particles to carry energy - radiation does not.
• Thermal radiation is energy transferred by infrared electromagnetic waves.
• Because these waves need no particles to travel through, radiation is the only method that works through a vacuum (such as energy reaching Earth from the Sun).
• Every object emits infrared radiation all the time, and the hotter an object is, the more radiation it emits.