Conduction, Convection & Radiation

Conduction definition

Transfer of thermal energy through solids by particle vibration

Best conductors

Metals

Why metals conduct well

Free electrons transfer energy quickly

Poor conductors

Insulators like wood, plastic, air

Conduction in liquids and gases

Very poor because particles are far apart

Convection definition

Transfer of heat by movement of fluids (liquids or gases)

Convection process

Warm fluid rises, cool fluid sinks → convection current

Why warm air rises

It becomes less dense

Why cool air sinks

It becomes more dense

Examples of convection

Heating a room, boiling water, sea breezes

Radiation definition

Transfer of energy by infrared waves

Medium needed for radiation

None; can travel through vacuum

Best absorbers of IR

Dark, matte surfaces

Best emitters of IR

Dark, matte surfaces

Worst absorbers/emitters

Light, shiny surfaces

Best reflectors of IR

Shiny surfaces

Vacuum flask design

Uses shiny surfaces to reduce radiation

Insulation purpose

Reduce conduction, convection and radiation

Loft insulation

Traps air → reduces convection and conduction

Cavity wall insulation

Foam reduces conduction; trapped air reduces convection

Double glazing

Air gap reduces conduction and convection

Key idea

Heat transfer occurs by conduction, convection or radiation depending on medium