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[Phys-l] Blackbody radiation



After my son asked me some questions about blackbody radiation I realize I have questions of my own about the usual textbook treatment of BBR.

Basically I don't understand the standing wave approach to BBR. I know it is historic, but the historic approach doesn't yield the correct result. Although I understand standing waves in excited cavities such as klystron tubes and magnetrons, using standing waves for a heated cavity doesn't seem right once we know about quantized atomic structure and emission of photons from atomic transitions.

First of all, hot objects that are not cavities will emit radiation that is nearly BBR. That is, the cavity is not really necessary for getting the basic BBR curves. The sun is not a cavity radiator. So what do standing waves have to do with BBR from hot objects that don't have cavities?

Second, the idea that the cavity walls must be electric field nodes doesn't seem quite right if the source of the photons is electronic transistions in the atoms on the surface of the walls.

Modern physics textbooks on my shelf explain the historic standing wave approach leading to the Rayleigh-Jeans result, but then continue using the standing wave approach when switvhing over to the Planck quantum picture. That doesn't make sense to me. Am I missing something?

Michael D. Edmiston, Ph.D.
Professor of Physics and Chemistry
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu