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I remember/memorized the derivation quite a few years ago. Reif's book is where I learned it. The derivation has a number of steps in it. First it counts photon modes in k-space. Then it converts to spherical k-space coordinates. It picks up a factor of 2 for polarization. This is all inside an enclosed cavity. Then it puts in the Bose factor for the mean occupation number at energy E. Next it computes by the effusion formula ## R=nv_{mean}/4 ## for the number of particles (photons) per unit time per unit area that will emerge from a small aperture (The effusion formula works for any gas where collisions are minimal. Treating the enclosed radiation as a collection of photons (particles) gets the correct answer. In this case ## v_{mean}=c ##). Finally, this is converted to an energy spectrum using ## e_p=hc/\lambda ##. The result is the Planck spectral blackbody function. (One sort of unanswered question in Reif's presentation is why the chemical potential ## \mu ## in the Bose factor is necessarily zero for a collection of photons. In any case, it gets the correct result.)greswd said:After you click on the link, it says "2 Items". Then click on "Reif Fundamentals" which is on the left. It should open the book right away.
The reason I have to ask you this is because I want make sure that what you said in #65 is not just a derivation of Planck's Law
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