Thermal energy transfer

Thermal energy can be transferred by:

• conduction

• convection

• radiation

Conduction

When a substance is heated, its particles gain energy and vibrate more vigorously. The particles bump into nearby particles and make them vibrate more. This passes the thermal energy through the substance by conduction, from the hot end to the cold end.

Stages in conduction

1. Back
2. 1
3. 2
4. 3
5. Next

This is how the handle of a metal spoon soon gets hot when the spoon is put into a hot drink.

• Substances that allow thermal energy to move easily through them are called conductors. Metals are good conductors of thermal energy.

• Substances that do not allow thermal energy to move through them easily are called insulators. Air and plastics are insulators.

Convection

The particles in liquids and gases can move from place to place. Convection happens when particles with a lot of thermal energy in a liquid or gas move, and take the place of particles with less thermal energy. Thermal energy is transferred from hot places to cold places by convection.

Radiation

All objects transfer thermal energy by infrared radiation. The hotter an object is, the more infrared radiation it gives off.

No particles are involved in radiation, unlike conduction and convection. This means that thermal energy transfer by radiation can even work in space, but conduction and convection cannot.

• Radiation is how we can feel the heat of the Sun, even though it is millions of kilometres away in space.

• Infrared cameras give images even in the dark, because they are detecting heat, not visible light.