Need help understanding black body radiation

AI Thread Summary
Black body radiation refers to the electromagnetic radiation emitted by a perfect black body, which is an idealized physical object that absorbs all incoming radiation and re-emits energy at a specific temperature. In simple terms, it represents equilibrium electromagnetic radiation within a closed volume. A practical example is a heated piece of iron that glows when it reaches high temperatures, emitting heat without reflecting light. The discussion highlights that while real objects do not perfectly radiate energy, they can be approximated using a concept called emissivity. The relevance of black body radiation to Big Bang cosmology lies in its role in understanding the cosmic microwave background radiation, which is a remnant of the early universe's heat. The conversation also touches on how changes in volume can affect temperature in a closed system.
p.falk
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Hello,
New to this message board (and very happy to have found it).

I am reading a book on cosmology by Steven Weinberg... I am having a terrible time understanding what exactly black body radiation is. Could someone please describe it in the most accesible terms? Also, if you would please explain the relevance of it to Big Bang cosmology...
Thank you very much!
 
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p.[B said:
falk]Hel[/B]lo,
New to this message board (and very happy to have found it).

I am reading a book on cosmology by Steven Weinberg... I am having a terrible time understanding what exactly black body radiation is. Could someone please describe it in the most accesible terms? Also, if you would please explain the relevance of it to Big Bang cosmology...
Thank you very much!


You mean THE BOOK BY STEVEN WEINBERG.In simpl terms "black body radiation" is EQUILIBRIUM ELECTROMAGNETIC RADIATION at temperature T which is found in closed volume V (a box).

This the oversimplified picture.

Daniel.
 
From an engineering standpoint, a black body is a body that perfectly radiates energy, i.e. heat. Real bodies do not radiate perfectly and are thus corrected by a term call emissivity.
 
Okay...
Let's see if I'm catching on.
A piece of iron heated to a very high temperature so that it would start to glow (giving off whitish/blue'ish light) would be an example of a blackbody. It doesn't reflect light that would shine upon it, but it does emit the heat that it absorbs.
If that piece of iron was a closed system that doesn't take in any more heat (from the outside of that closed system) and doesn't lose anymore heat (to the outside of that closed system) its temperature should remain constant.
But if the volume of that piece of iron were to expand the temperature would drop.
 
Don't mean to do this ^^^
But is my previous post close to being correct?
Thanks
 

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