Blackbody Radiation
“Blackbody radiation” or “cavity radiation” refers to an object or system which absorbs all radiation incident upon it and re-radiates energy which is characteristic of this radiating system only, not dependent upon the type of radiation which is incident upon it. The radiated energy can be considered to be produced by standing wave or resonant modes of the cavity which is radiating.
| The amount of radiation emitted in a given frequency range should be proportional to the number of modes in that range. The best of classical physics suggested that all modes had an equal chance of being produced, and that the number of modes went up proportional to the square of the frequency.But the predicted continual increase in radiated energy with frequency (dubbed the “ultraviolet catastrophe”) did not happen. Nature knew better. |  |
Planck Radiation Formula
From the assumption that the electromagnetic modes in a cavity were quantized in energy with the quantum energy equal to Planck’s constant times the frequency, Planck derived a radiation formula. The average energy per “mode” or “quantum” is the energy of the quantum times the probability that it will be occupied (the einstein bose distribution function):
This average energy times the density of such states expressed in terms of either frequency or wavelength
gives the energy density, the Planck radiation formula.
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The Planck radiation formula is an example of the distribution energy according to Bose-Einstein statistics
Rayleigh-Jeans vs Planck
Comparison of the classical Rayleigh-Jeans Law and the quantum planks rdiation formula . Experiment confirms the Planck relationship.
Blackbody Intensity as a Function of Frequency
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