Physics - Heat transfer

How can thermal energy transfer take place?

By conduction, convection or radiation

What is conduction?

The transfer of heat through a substance

What does conduction mainly happen in?

Metals because they contain free electrons which helps the heat travel faster

What is a conductor?

A substance or material that allows heat to flow e.g. a metal frying pan or a radiator

What is an insulator?

A substance or material which does not readily allow the passage of heat e.g. a wooden spoon or oven gloves

Conduction in non-metals

If heat energy is supplied to one part of a solid, the atoms vibrate faster. As they vibrate more, the bonds, between the atoms are shaken more. This passes vibrations through onto the next atom and so on until the energy eventually spreads throughout the solid. The overall temperature increases.

Conduction in metals

They are good conductors of heat so the atoms vibrate more when heated. The free electrons carry charge around as well. These transfer the energy much faster than just vibrations in bonds.

Why are liquids poorer conductors of heat than solids?

The particles in liquids are further apart than those in solids. Therefore heat cannot pass on easily in liquids

Why are gases the poorest conductors?

The particles are very far apart

What is a vacuum?

A space where there are no particles. If there are no particles to pass on the vibrations (and hence heat) by conduction, it is the perfect insulator of heat.

What is convection?

It is a process where heat is transferred through the movement of fluid (liquid or gas)

Convection diagram

Moves in a circular motion

What is radiation?

The transfer of heat energy from a region of high temperature to a region of low temperature using infra-red radiation

What does radiation travel by?

Electromagnetic waves

What does radiation not need?

Particles so can work through a vacuum

What is a our planet’s most important source of thermal radiation?

The sun

Things convection is used for

Radiators heating rooms, cooking food, weather patterns, ocean currents and movement of tectonic plates

What do hotter objects do?

Emit more radiation and therefore emit more visible light

Shiny and / or white surfaces

Poor absorbers and emitters of radiation

Dark and / or matte surfaces

Better absorbers and emitters of radiation

Practicals for conduction

Heat a boiling tube with ice cover by a gauze and water in it.
Heat one end of a piece of metal and count how long it takes to feel the heat
Holding a match closer and closer to a Bunsen burner until it catches flame

Practicals for convection

Square glass tube with purple dye

Smoke box experiment

Online sea breeze animation experiment

Practicals for radiation

Leslie’s cube

Preventing heat transfers

• Rubber stopper and glass walls = good insulators which reduces conduction

• Vacuum has no particles so both conduction and convection can’t take place

• Rubber stopper stops hot air rising, which reduces convection

• Shiny silvered walls = poor absorbers and emitters of radiation so reflects rays back and emits less rays outwards so reduces radiation