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=                          Planck postulate                          =
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                            Introduction
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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
:E=nh\nu\,,
where 'n' is an integer (1, 2, 3, ...), 'h' is Planck's constant, and
'\nu' (the Greek letter 'nu', not the Latin letter 'v') is the
frequency of the oscillator.

The 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 is now known) a fundamental change
in the understanding of the world. In other words, Planck then
contemplated virtual oscillators.

In 1905, 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.


                             References
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* Tipler, Paul A. (1978). 'Modern Physics'. Worth Publishers, Inc.
* [http://scienceworld.wolfram.com/physics/PlanckPostulate.html Planck
Postulate]�from 'Eric Weisstein's World of Physics'


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Original Article: http://en.wikipedia.org/wiki/Planck_postulate