Heat Transfer

Heat transfer

Conduction

Insulation

Convection

Radiation

Three Methods of Heat Transfer

CONDUCTION

CONVECTION

RADIATION

Radiation

Radiation is the only method of heat transfer that does not require particles as a medium. This means it is the only

method of heat transfer that can travel through a vacuum.

Heat radiation is emitted by all objects above

absolute zero and travels in straight lines.

RadiationRadiation is the only method of heat transfer that can travel through a vacuum.

Heat radiation is emitted by any body with a temperature above absolute zero.

Heat radiation is a type of electromagnetic radiation. Like all electromagnetic radiation it travels in straight lines and at the speed of light.

Bodies that give out heat radiation are known as emitters. Dull, black surfaces are the best surfaces for emitting radiation.

Bodies that take in heat radiation are known as absorbers. Dull, black surfaces are the best surfaces for absorbing radiation.

Shiny, white surfaces are very good at reflecting heat radiation.

Good Reflectors

Buildings in the Mediterranean are often painted white. This is because white surfaces are good reflectors of the heat radiation. This means that during the day it helps to

keep the insides of buildings as cool as possible by reflecting heat radiation away from the building.

Good Reflectors

Teapots are often shiny. This is because shiny surfaces are good reflectors of heat radiation. The shiny surface of the teapot will therefore reflect any heat radiation trying to

escape from the teapot back in. This means any tea poured into the teapot will stay warmer for longer.

Exercise 15: Radiation

Why are buildings in the Mediterranean often painted white?

Exercise 16: Insert the Missing Words

_________ is the only method of heat transfer that can travel through a _______.

Heat radiation is emitted by any body with a ___________ above absolute zero.

Heat radiation is a type of ______________ radiation. Like all electromagnetic radiation it travels in _______ lines and at the speed of _____.

Bodies that give out heat radiation are known as emitters. Dull, ______ surfaces are the best surfaces for emitting radiation.

Bodies that take in heat radiation are known as absorbers. Dull, black surfaces are the best surfaces for absorbing radiation.

Shiny, _____ surfaces are very good at _________ heat radiation.

Radiationvacuum

temperature

electromagneticstraight

light

black

white reflecting

Exercise 17: Radiation1. What do light and heat radiation have in common?

2. If you wish to stay cool on a hot, sunny day, which colour T-shirt would you wear. White or black?

3. Why?

They are both types of electromagnetic radiation, they both travel at the speed of light, they both travel in straight line and they can both travel across a vacuum.

White

White is a good reflector of heat radiation, whereas black is a good absorber of heat radiation. If you wore a black T-shirt on a hot, sunny day then the T-shirt would absorb a high percentage of the incident heat radiation and you would thus feel warmer. Whereas if you wore a white T-shirt on a hot, sunny day more of the incident heat radiation would be reflected and you would feel cooler.