Planck postulate

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The Planck postulate (or Planck's postulate), one of the fundamental principles of quantum mechanics, is the postulate that the energy of oscillators in a black body is quantized, and is given by


where is an integer (1, 2, 3, ...), is Planck's constant, and (the Greek letter nu, not the Latin letter v) is the frequency of the oscillator.

The Planck Postulate was introduced by Max Planck in his derivation of his law of black body radiation in 1900. This assumption allowed Planck to derive a formula for the entire spectrum of the radiation emitted by a black body. Planck was unable to justify this assumption based on classical physics; he considered quantization as being purely a mathematical trick, rather than (as we now know) a fundamental change in our understanding of the world.[1] In other words, Planck then contemplated virtual oscillators.

In 1905 in one of his three most important papers, Albert Einstein adapted the Planck postulate to explain the photoelectric effect, but Einstein proposed that the energy of photons themselves was quantized, and that quantization was not merely a feature of microscopic oscillators. Planck's postulate was further applied to understanding the Compton effect, and was applied by Niels Bohr to explain the emission spectrum of the hydrogen atom and derive the correct value of the Rydberg constant.


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  • Tipler, Paul A. (1978). Modern Physics, Worth Publishers, Inc.
  • Planck Postulate — from Eric Weisstein's World of Physics