Three Methods of Heat Transfer
1. Conduction
Heat travels through a solid (or stationary liquid) from particle to particle. Particles vibrate and pass energy to neighbours.
Best conductors: metals (copper, iron)
Best insulators: wood, plastic, air, glass wool
A metal spoon in hot soup gets warm throughout.
Energy travels from the hot soup → through the metal → to your hand.
2. Convection
Heat travels in moving fluids (liquids and gases). Hot fluid rises (less dense), cool fluid sinks (denser), forming convection currents.
Heating a room with a radiator
Air next to the radiator warms and rises → cool air flows in at the bottom → a convection current circulates warm air around the room.
3. Radiation
Heat travels as electromagnetic waves (infrared radiation). No material needed — works in a vacuum.
Good absorbers/emitters: dull, dark surfaces
Good reflectors: shiny, light surfaces
Feeling warm from the Sun
Infrared radiation travels 150 million km through space (vacuum) to warm your skin.
Summary Table
| Method | Medium needed | Particles move? |
|---|---|---|
| Conduction | Solid (or still fluid) | No |
| Convection | Fluid (liquid/gas) | Yes |
| Radiation | None | N/A |
Real world: Double-glazed windows
Modern windows use two panes of glass with a sealed air gap (or argon gas) between them. Air is a poor conductor, so very little heat escapes by conduction. This can cut heat loss through windows by about 50% compared with single glazing, saving energy and money.
Real world: Sea breezes
On a sunny day, land heats up faster than the sea. The hot air above land rises (convection), and cooler air from the sea flows in to replace it — creating a sea breeze. At night the process reverses, forming a land breeze. These are large-scale convection currents driven by uneven heating.
Real world: Thermal (emergency) foil blankets
Shiny metallic emergency blankets reflect up to 90% of the body's infrared radiation back to the casualty, drastically reducing heat loss by radiation. The thin layer of trapped air also reduces conduction and convection loss.
Practice Problems
Explain why a wooden handle on a metal pan stays cool.
Show answer
Why does heat travel from the Sun to Earth through space?