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Derivation of Rayleigh–Jeans law

  1. Jun 18, 2011 #1
    I have read the derivation of the Rayleigh-Jeans law from:

    This derivation is quite similar to the derivation in my textbook.

    My question is why the frequency/wavelength is quantized, but there still a d[itex]\nu[/itex] or d[itex]\lambda[/itex]. Not this "d" only apply to continuous variables?

    And since the frequency is quantized, that means the emission spectrum is not continuous? But my textbook said "condensed state emits a continuous spectrum of radiation."
  2. jcsd
  3. Jun 18, 2011 #2


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    It's the energy which is quantized, not the frequency. You can have a photon of any frequency. But then E = n hω

    (Derivations of this and other formulas often work in a large box of side L for convenience, to help with the normalization. In a box of side L the wavelength must be a submultiple of L. Afterwards, however, you let L -> ∞, and this restriction disappears.)
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