Conduction, Convection and Radiation notes

From hotter areas to colder areas

Direction of transfer of thermal energy

Conduction

Convection

Radiation

Ways thermal energy can be transferred (3)

Main method of thermal energy transfer in solids

Conduction

Free delocalised electrons collide with atoms, helping to transfer vibrations through the material and hence transfer heat through the metal quickly

Metal are very good conductors

Strong intermolecular bonds between particles make transfer of KE more rapid

Solids are good conductors

Non-metals, liquids and gases

Insulators

Atoms bump into eachother transferring KE

Intermolecular forces allow vibrations to pass between them

Heating a substance (2)

The transfer of heat through fluids (liquids and gases)

Convection

A fluid is heated

Molecules are pushed apart and the fluid expands

Hot fluid becomes less dense than surroundings

It rises and cold fluid (surroundings) moves to take its place

Hot fluid eventually calls and sinks back down again

Convection current (5)

The transfer of heat energy by IR waves

Thermal radiation

Emits more IR in a given time

A hotter object

Good absorber and emitter

Black surface

Poor absorber and emitter

White surface

Ok absorber and emitter

Dull/rough surface

Very poor absorber and emitter

Shiny surface

Can only occur through radiation, not conduction or convection

Heat transfer in a vacuum