P1aL2 Thermal Radiation

Key Words

Absorb - take in thermal radiation

Emit - give out thermal radiation

Global Warming - average temperatures across our planet are rising.

Heat energy - energy flowing from a hot object to a cold object

Thermal radiation - electromagnetic radiation given out by hot objects.  Behaves just like light.

Thermopile - a scientific instrument to measure radiation.

Grade E

All hot objects emit radiation which you can feel with your hand.  You can detect thermal radiation with a thermopile.

Experiments with a Leslie's Cube filled with hot water tell us:

• black surfaces emit more radiation than white surfaces;

• dull (matt) surfaces emit more radiation than shiny surfaces.

Grade C

Dull black surfaces absorb more radiation than white shiny surfaces.  White surfaces reflect radiation.  Some important uses:

• Cooling fins on heat exchangers are best coloured matt black to emit more thermal radiation.
• Houses in hot countries are often pained white to reflect thermal radiation.
• A fell-runner suffering from hypothermia (has got too cold) is wrapped up in a space blanket which is made of highly reflective foil.

Thermal radiation is an important factor in global warming.  The ice on the poles reflects a lot of heat while the dark blue ocean absorb a lot of heat.  Loss of the ice caps will make global warming more serious.

Grade A

Polar bears have what fur that acts like light tubes to guide thermal radiation to black skein that absorbs the radiation.  The fur traps air which is a very good insulator, so it does not matter that the black skin is a very good thermal emitter.