(no subject)

Glenn Rankin (rankin@hplabsz.hpl.hp.com)
Mon, 31 Jan 94 13:43:05 PST

Rick Walker writes:
> Every bit of energy you put in comes out as "light". However, only a
> very small fraction of that "light" is visible. Most of it is at such a
> long wavelength that it is usually called "heat". (eg: blackbody
> radiation at 2500-3500K).

Many may consider what I am about to write a nit, but as a physicist,
I couldn't let the above pass without comment. Heat comes out as light
(visible and invisible -- electromagnetic energy if you wish) _and_ as
thermal motion (kinetic energy) of the surrounding matter. That's why
fans can help cool things down by moving hot air away and cool air
towards the source of heat. The fan generally doesn't affect light
much. It is true that if matter and the electromagnetic fields in a
volume are in equilibrium, then their energy spectra can be
characterized by the same temperature.