Thermal (Infrared) Radiation is the transfer of heat energy by electromagnetic waves<-- that's why it can travel in a vacuum, because it has no particles
Conduction and Convection is the transfer of heat energy by particles
Amount of heat radiation depends on surface area:
This is why car engines have fins
The bigger the surface area exposed to the heat radiation the quicker it'll heat up
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Radiation
Dark matt surfaces absorb heat radiation better than bright glossy surfaces and emit more heat
Silvered surfaces reflect nearly all heat radiation falling on them
That's why you get black solar panels and silver survival blankets
Experiments to denmonstrate this:
Leslie's Cube
Melting Wax Trick
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Conduction
Main form of heat transfer in solids
Process where VIBRATING PARTICLES pass on their EXTRA KINETIC ENERGY to NEIGHBOURING PARTICLES
Metals conduct so well because of their free electrons:
At the hot end electrons move faster and collide with other free electrons, transferring energy
Because the electrons can move freely it's a much quicker way of transferring heat through the metal than slowly passing it between jostling neighbouring atoms
The further the electrons have to transfer energy the less efficient it is
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Convection
Convection occurs when the more energetic particles MOVE from the HOTTER REGION to the COOLER REGION - AND TAKE THEIR HEAT ENERGY WITH THEM
Liquid particles, when heated, start moving around faster meaning there's a greater distance between them ----> the water expands and becomes less dense
Convection currents are all about CHANGES IN DENSITY
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Useful Heat Transfers - Thermos Flask
Why is a Thermos Flask a good insulator?
Glass bottle is double-walled meaning it has a vacuum between the two walls <-- stops all convection and conduction through the sides
Walls of inner flask are silvered to reduce radiation
The bottle is supported using insulating foam, this reduces conduction to or from the outer glass bottle
The stopper is made out of plastic filled with cork or foam to reduce conduction
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