Conduction, convection and radiation

Heat moves from hotter places to colder ones in three ways: conduction through solids, convection in liquids and gases, and radiation, which needs no material at all.

Key facts

  • Conduction: vibrating particles pass energy on; metals are the best conductors.
  • Convection: warm fluid rises, cool fluid sinks, making a current.
  • Radiation: infrared waves; dark, matt surfaces absorb and emit best.
  • Insulators like trapped air slow heat transfer.

Worked examples

Example 1

Why does a radiator heat a whole room even though it’s only on one wall?

  1. Air near the radiator warms, expands, becomes less dense and rises.
  2. Cooler air sinks to take its place, setting up a convection current round the room.

Answer: Convection currents

Example 2

Why are saucepans made of metal with plastic handles?

  1. Metal conducts heat quickly to the food.
  2. Plastic is an insulator, so the handle stays cool.

Answer: Metal conducts, plastic insulates