AQA GCSE Perfect Black Body(Physics)

Perfect Black Body

Black surfaces are good absorbers of infrared radiation.

We can define a perfect black body as:

An object that absorbs all of the radiation incident on it

This means that a perfect black body will not reflect or transmit any radiation. 

In the diagram below the black sphere is acting as a perfect black body absorbing all of the incident radiation and transmitting or reflecting none. 

A perfect black body as a sphere absorbing all of the incident radiation

Perfect black bodies as emitters.

Any body that is a good absorber, is also a good emitter.

This means that a perfect black body is also the best possible emitter of radiation. 

When the black body absorbs the incident radiation, its temperature increases, as a result it will then emit radiation. 

Perfect black body absorbing incident radiation and then emitting incident radiaiton

Perfect Black Body and Temperature

The temperature of a perfect black body depends on the rate of absorbtion of incident and the rate of  emitted radiation.

Rate of energy absorbed > Rate of energy emitted then temperature increases

Rate of energy absorbed = Rate of energy emitted then temperature is constant

Rate of energy absorbed < Rate of energy emitted then temperature decreases

Practice Question

1.Define the term perfect black body

2.In the table below tick the boxes next to the correct statements for a perfect black body

StatementTick if correct
Absorbs all of the incident radiation
Can reflect radiation
Can transmit radiation
Is the best possible emitter

3. A perfect black body has a constant temperature. What can you deduce about the incident and emitted radiation for the perfect black body?

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