Radiation

Radiation 

Thermal radiation is mainly infra-red waves, but very hot objects also give out light waves. Infra-red radiation is part of the electromagnetic spectrum 

• thermal energy transfer by radiation does not require a medium 
  

An emitter sends out thermal radiation. A reflector reflects thermal radiation, therefore is a bad absorber. An emitter will cool down quickly, an absorber will heat up more quickly and a reflector will not heat up quickly.

	Matt Black	White	Silver
Emitter	best		worst
Reflector	worst		best
Absorber	best		Worst

The amount of radiation emitted by a body depends on its temperature, and is proportional to T⁴. This relation shows that as the temperature of the object increases, the amount of radiation emitted increases very rapidly. The emitted radiation will travel at the speed of light until it is absorbed by another body. The absorbing medium can be gas, liquid, or solid. Radiation does not require a medium to pass through. This is demonstrated by solar radiation which pass through interplanetary space to reach the earth.

Consequences of energy transfer 

Applications
-solar panel: the sun’s thermal radiation is absorbed by a matt black surface and warms up the pipes containing water -refrigerator: the freezer compartment is located at the top of the refrigerator. It cools down the air which then sinks. Any warm air rises to the top and then is cooled. This creates a convection current which maintains a cold temperature. -metals are used in cooking pans because they conduct the heat well
Consequences
-a metal spoon in a hot drink will warm up because it conducts the heat
-Convection currents create sea breezes. During the day the land is warmer and acts as heat source. During the night the sea acts as the heat source.

a black saucepan cools better than a white one, white houses stay cooler than dark ones.