Modes of Heat TransferConductionConvectionRadiationConduction is the transfer of thermal energythrough a substance , or between substances incontact, by the collision of particles.Conduction occurs in solids and liquids.Convection is how the air contacted with heatmaterial, which takes it to other materials withdifferent temperatures.Convection occurs in liquids and gases.The process in which energy is transferred waves. It is the combined processes ofemission, transmission, and absorption of heat orlight.
CONDUCTIONMolecularvibrationFree electrondiffusionOccurs in allsolidsSlow processOccurs in metalsonlyFast process Two types of conduction Molecular vibration Free electron diffusionConductors and InsulatorsMaterials that can conduct heat easily andreadily (eg. Metals) are known as conductors.Materials that do not conduct heat easily (eg.Water, air, plastic) are known as insulators.
What happens duringconvection?1• Water at the bottom is heated first.• Heated water expands.2• When water expands density decreases• Heated water of lower density starts to rise.3• Cooler water of higher density rushes in from sides totake its place.• The cooler water gets heated and the cycle repeats.Convection currents are set up.Taking the example of heating water.Convection
Hot waterrisesCoolerwatersinksCools atthesurface
Convection helps to make the Earth liveable asit removes excess heat from the Earth andtransporting it high up into the atmosphere.
Applications of convection.Air con is usually placed atthe top of a room.Heating coil of a kettle isusually at the bottomFormation of land and seabreezes
RadiationRadiation does not require a medium totransfer heat. (can occur in a vacuum)Sun releases electromagnetic waves (heatis contained in the waves as infra-red)Hotter objects radiates more heat.
Page 10Emitters and absorbers The Sun gives out the heat. It is known as an emitter / radiator The Earth takes in the heat. It is known as an absorber. A good emitter would also be a good absorber. A poor emitter would be a poor absorber.Goodemitter/absorberPooremitter/absorberDull, blacksurfaceRough surfaceShiny, silversurfaceSmooth surface