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.
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 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
Statement | Tick 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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