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Q & A: thermal radiation equilibrium

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Most recent answer: 10/22/2007
Q:
I have a different box question from the light box question. If I have a closed box that is mirrored on 5 sides inside the box and the 6th side is painted black, will the black side be warmer than the center of the box
- Steve
Burbank CA
A:
If you just let the box sit, isolated from inputs and outputs, the different sides will reach the same temperature. That's a very direct result from the deepest laws of thermodynamics.

How can that work, when the black side is so much better at absorbing radiation than the shiny sides? The black side is also much better at emitting radiation. So on the average, the radiation flow between any two sides is equal both directions just when they're at the same temperature, even if one is a good emitter/absorber and the other isn't.

Mike W.

(published on 10/22/2007)

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