Clarification of Black Body Radiation

[Minki]

Hi, I'm trying to understand black body radiation but I have two conflicting descriptions (both reputable sources). Maybe both are true, but I need some clarification please:

1. A black body is a perfect emitter – it will emit equally well at any wavelength.

2. The black body re-radiates energy which is characteristic of this object only.

Thanks.

 

[G01]

Hi, I'm trying to understand black body radiation but I have two conflicting descriptions (both reputable sources). Maybe both are true, but I need some clarification please:

1. A black body is a perfect emitter – it will emit equally well at any wavelength.

I think what this statement is saying is that, on a totally classical level, a blackbody has a equal chance of radiating into any allowed frequency mode. Since the number of allowed modes increases with the square of the frequency, this results in a parabolic emission curve. However, there is obviously a problem. The parabola grows without bound and the black body is predicted to emit absurdly large amounts of energy at high frequencies.

The quantum theory of black body emission fixes this problem. When analyzed using quantum theory, the blackbody emission curve has a peak at a certain frequency and the emitted radiation intensity drops to zero for high frequencies.

2. The black body re-radiates energy which is characteristic of this object only.

This is correct. The blackbody radiation curve depends only on the temperature of the object.

For more info:

http://hyperphysics.phy-astr.gsu.edu/hbase/mod6.html

 

[Minki]

Thanks GO1, that sorts it. The second statement did actually come from that link.