Need help understanding black body radiation

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Discussion Overview

The discussion revolves around the concept of black body radiation, particularly its definition and relevance to Big Bang cosmology. Participants seek to clarify the nature of black body radiation and its implications in a cosmological context.

Discussion Character

  • Exploratory
  • Conceptual clarification

Main Points Raised

  • One participant requests a simple explanation of black body radiation and its relevance to Big Bang cosmology.
  • Another participant describes black body radiation as equilibrium electromagnetic radiation at a temperature T within a closed volume, noting that this is an oversimplified view.
  • A different perspective from an engineering standpoint defines a black body as an entity that perfectly radiates energy, contrasting it with real bodies that have emissivity corrections.
  • A participant provides an example of a heated piece of iron as a black body, discussing its emission of heat and the effects of volume expansion on temperature.
  • One participant seeks validation for their understanding of black body radiation based on their previous explanation.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and provide different definitions and examples of black body radiation, indicating that multiple competing views remain without a consensus on a singular explanation.

Contextual Notes

Some definitions and explanations may depend on specific assumptions about ideal versus real bodies, and the implications of temperature changes in closed systems are not fully resolved.

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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