Definition
Conduction transfers heat through direct contact between particles, which vibrate and pass energy to their neighbours, without the particles themselves travelling far.
Metals conduct heat much faster than non-metals because their free (delocalized) electrons carry energy through the material quickly, in addition to particle vibration.
Definition
Convection transfers heat by the actual bulk movement of a fluid (liquid or gas): heated fluid becomes less dense, rises, and is replaced by cooler, denser fluid, setting up a convection current.
Convection cannot occur in solids, since their particles are fixed in place and can't flow.
Example 1 — land and sea breeze
Explain what causes a sea breeze during the day.
- Land heats up faster than the sea in sunlight.
- Air above the land warms, becomes less dense, and rises.
- Cooler, denser air from over the sea flows in to replace it — this incoming flow is the sea breeze.
Answer: Uneven heating of land and sea sets up a convection current
Remember
Birds and gliders use rising columns of warm air (thermals, a convection effect) to gain height without flapping — they circle within the rising air current.
Definition
Radiation transfers heat as electromagnetic waves, needing no medium at all — this is how the Sun's heat crosses the vacuum of space to reach Earth.
Dull, black surfaces absorb and emit radiation better than shiny, silver surfaces, which mostly reflect it — confirmed by the Leslie's cube experiment, where the black face radiates noticeably more heat than the polished face at the same temperature.
Remember
A radiator with a larger surface area emits more heat by radiation in the same time — this is why radiators are built with fins/ridges rather than a smooth flat surface.
Sunlight (mostly visible light) passes through the atmosphere and warms Earth's surface; the surface then re-radiates this as infrared (heat) radiation, some of which greenhouse gases absorb and re-emit back downward — this natural greenhouse effect keeps Earth's average temperature high enough to support life, but an enhanced effect (from added greenhouse gases) causes excess warming.
Quick Recap
- ●Conduction: particle-to-particle contact, no bulk movement; metals conduct fastest (free electrons)
- ●Convection: bulk fluid movement, warm fluid rises; impossible in solids
- ●Radiation: electromagnetic waves, no medium needed; dull black surfaces absorb/emit best
- ●Greenhouse effect: surface re-radiates absorbed sunlight as heat, some trapped by greenhouse gases
