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Planck's law derivation

  1. Jun 15, 2014 #1
    The derivation of Planck's law in my textbook begins with the assumption that the energy of an oscillator with frequency ##\nu## is quantised in units of ##h\nu##. It follows that the average energy of such an oscillator (in equilibrium with a reservoir at temperature ##T##) will be

    Then, the textbook asserts that the average energy of a mode of electromagnetic radiation with frequency ##\nu## will be the same, and I don't see why this should be true.
  2. jcsd
  3. Jun 15, 2014 #2

    Andrew Mason

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    I think they are just saying that electromagnetic radiation in a resonating (black-body) cavity at temperature T behaves in a way that is analogous to the quantum oscillator: ie. the distribution of energies of electromagnetic waves inside the resonating cavity is given by Planck's law.

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