Question

Quantum Mechanics

Answer 1

Its to do with black body radiation, it says that when it absorbs the EMR( which is basically absorbing energy) by absorbing energy, higher frequency and higher and higher being re emitted. - classical physics

however according to modern physics it says that intensity of re-emitted radiation does increase UNTIL it reaches a particular frequency that depends on the temperature, and then drops.

1. is that particular frequency the "peak frequency"
2. what does it mean by depend on temperature and then drops? what drops?
3.Also it says higher the temp, higher the peak frequency what does that mean?

Answer 2

@mstoldegon

Answer 3

3. edited- higher the temp, higher the peak frequency shift ups to

Answer 4

I'm a little confused. A classical black body does not reflect or re-emit radiation.
As a true black body (other than a Black Hole) doesn't actually exist, the body will continue to absorb the radiation - typically without re-radiating any radiation in the higher frequencies (shorter wavelengths) that it might have absorbed - but will increase its own energy level because of the energy it has absorbed. As the temperature of the Black Body increases, it will start radiating in higher frequencies. The hotter it gets, the higher the frequency of the radiated energy.
Would you like an example??

Answer 5

In regards to the "Modern Physics" interpretation, it may be that the reference to the energy dropping might be when the BB has reached its maximum frequency of radiation (its highest temperature), if the source of energy was terminated, it would start to cool and therefore the frequency of the re-radiated energy would also drop. Could this be what you are looking for?

Answer 6

@mstoldegon you have misunderstood the properties of a black body, they are equally good emitters as absorbers of radiation, this is Kirchoff's law.

@dareintheren What is being discussed here is the energy density of black body radiation as a function of frequency. Classical physics wrongly predicted that the energy density would increase without limit as the frequency of the radiation increased.
Max Planck fiddled around and found a mathematical function that correctly described the true energy density, and in the process he started the beginnings of quantum mechanics.
You can find more details and a diagram here, better than me trying to type it all out
http://en.wikipedia.org/wiki/Planck's_law
note that the graph here is plotted against wavelength, and higher frequency corresponds to smaller wavelength

Answer 7

The diagram in the wikipedia article gives the Planck curve for three different temperatures, showing how the peak of the curve occurs at different wavelength (frequency) for different temperatures

Answer 8

https://www.google.com/oitrig

Answer 9

Are you OK on understanding a "Black Body" or would you like an "Applied Physics" answer (my area of knowledge)?
I understand what ProfBrainstorm said and, yes, I do know they are Emitters as well as Absorbers.
There are some characteristics of Black Body physics that applies in the real world but many people don't know/understand them.
If its too late, no prob.