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Conduction, Convection & Radiation

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Conduction, conductors and insulators

Conduction is the main route by which heating moves energy through solids. Metals conduct superbly; non-metals, liquids and gases barely conduct at all — and the poor conductors earn a name of their own, insulators, which is exactly what you want under your feet on a cold bathroom floor.

What you know already

Heating moves energy three ways: through solids by colliding particles (conduction, turbocharged in metals by delocalised electrons), through fluids by density-driven currents (convection), and through nothing at all by infrared waves (radiation). The surface and the state of matter decide which route wins.

Key points of understanding

Conduction moves heating energy through solids by particle jostling.
Metals are extremely good thermal conductors.
Non-metals conduct poorly, and liquids and gases barely conduct at all.
Poor conductors are called insulators, and they prevent energy transfer by conduction.
Materials containing pockets of trapped air are especially good insulators because air is a gas and cannot form convection currents when trapped.

2-3-1-demo-thermal-conduction-feet-on-rug-with-note-cie-igcse-23-rn — Energy is transferred by heating from the hotter foot to the cooler tiles by conduction

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1.Conduction, conductors and insulators

4.6

Key points

Conduction moves heating energy through solids by particle jostling.
Metals are extremely good thermal conductors.
Non-metals conduct poorly, and liquids and gases barely conduct at all.

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2.How conduction works, and why metals win

4.6

Heat one end of a solid and its atoms vibrate harder, jostling their neighbours and passing energy along atom by atom. Metals add a second delivery service: their delocalised electrons roam freely and collide with atoms, carrying the vibrations — and the heat — far faster than the lattice alone could.

Conduction, IGCSE & GCSE Physics revision notes — Conduction: the atoms in a solid vibrate and bump into each other

Free Electrons Conductor, downloadable IGCSE & GCSE Physics revision notes — Delocalised electrons in metals speed up thermal conduction in metals

3.Convection and convection currents

4.7

Fluids — liquids and gases — carry heat by moving themselves: convection. Warm fluid expands, becomes less dense than its surroundings, and rises; cooler fluid sinks into its place; the cycle draws a convection current. Solids are excluded — nothing flows — which is why the mechanism belongs to fluids alone.

Convection, IGCSE & GCSE Physics revision notes — A convection current caused by heating from the fire

4.Thermal radiation and the mug of coffee

4.8

Every object, whatever its temperature, emits infrared radiation — no particles, no medium, just waves. Hotter objects radiate more per second, and the surface decides how well: black surfaces are the best emitters and absorbers, shiny surfaces the worst. A cooling mug of coffee runs all three transfer routes at once.

Leslie-cube, IGCSE & GCSE Physics revision notes — The infrared radiation emitted from a hot object can be detected using a special camera

Heat loss, downloadable IGCSE & GCSE Physics revision notes — Energy is transferred by conduction, convection and radiation in a mug of hot coffee