Physicspunks

[georgemw at speakeasy.net]

On 17 Aug 2001, at 16:17, An Metet wrote:


> 
> But, in the case described the two bodies start out at the same
> temperature.  One radiates more energy towards the other one at that
> particular temperature.  So, you would expect that one body would
> become hotter than the other.
>

The important fact that you seem to be unaware of
is that the body that radiates faster also
absorbs more (reflects less).  A black plate will
radiate faster than a white one,  but the white plate
is reflecting almost all the light that hits.
Cavity radiation and blackbody radiation are used synonymously.

George
> From the hints you've dropped I see the general outline of the
> solution.  The photons going between the two blocks of metal will
> "thermalize" and the volume between the two blocks will look like the
> inside of a cavity.  The rate of energy transfer in each direction
> will then be the same.
> 
> In fact, if the two blocks were contained in a large thermos which
> perfectly reflected the photons, the same effect would occur.  It
> would be like an inside out cavity.  Each block would end up at the
> same temperature.  (Perhaps slightly lower than the start temperature
> because it must take some energy to fill the space with thermalized
> photons.)