chapter 11 Flashcards
conduction
main method of thermal energy transfer in solids
- metals are good at conducting heat
- poor conductors = insulators
- materials containing small pockets of trapped air are good at insulating as air is a gas and hence a poor conductor
conduction occur?
the atoms in a solid vibrate and bump into each other, lattice vibration of copper ions and the movement of delocalised electrons
Eg metals are good at conducting
convection
main way heat travels through liquid and gasses
- when liquid or gasses are heated the particles push each other apart making gas/liquid expand making them less dense than surroundings
- the hot liquid/gas rises, the cooler surrounding liquid/gasses move into take their place
- eventually the liquid/gas cools, contracts and sinks back down
=the resulting motion is call convection
convection def
heat energy transfer in liquid or gas resulting in the change of density
radiation
-all hot objects give off thermal radiation =hotter they are, more they emit
thermal radiation = infrared (electromagnetic spectrum)
-thermal radiation is the only way heat can travel through a vacuum
darker = good absorber and good emitter lighter = poor absorber and poor emitter
factors affecting emissions of radiation
- temp = hotter = more radiation
- colour= black = more radiation
- surface area = greater = more area for radiation to be emitted from
home insulation
- think curtains, draught excluders = stops convection currents, prevents cold area entering and warm leaving
- loft and underfloor insulating materials = prevents conduction of heat through floors and ceilings
- double and triple glazing windows = vacuum between glass panes cuts out losses by conduction convection
- cavity walls =reduces heat losses by conduction
- foam or rockwool in wall cavity = further reduces heat losses by convection
convection, climate and weather
convection currents are the orgins of winds and ocean currents, two major factors that control climate patterns around the world
