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# Planck's constant

noun, Physics.
1.
the fundamental constant of quantum mechanics, expressing the ratio of the energy of one quantum of radiation to the frequency of the radiation and approximately equal to 6.624 × 10− 27 erg-seconds. Symbol: h.
Also, Planck constant.
Origin
1905-1910
1905-10; named after M. K. E. Planck
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Based on the Random House Dictionary, © Random House, Inc. 2014.
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plancks constant in Medicine

Planck's constant (plängks)
n.

Symbol h The constant of proportionality relating the energy of a photon to the frequency of that photon. Its value is approximately 6.626 × 10-34 joule-second.

The American Heritage® Stedman's Medical Dictionary
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plancks constant in Science
 Planck's constant   (plängks)    A physical constant that is used extensively in quantum mechanics and fixes the scale of quantization of many phenomena, such as the relation between the energy of a photon (a quantum of light) and its wavelength. Its value is approximately 6.626 × 10-34 joule-seconds (equivalent to units of angular momentum). Planck's constant is fundamental to phenomena as the quantization of angular momentum and is used in Heisenberg's Uncertainty Principle. See also Dirac's constant, quantize.
The American Heritage® Science Dictionary
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plancks constant in Culture

### Planck's constant definition

A universal constant, first discovered by Max Planck, that states the mathematical relationship between the frequency of an electromagnetic wave and the energy in that wave. Planck's discovery unifies the seemingly contradictory observations that energy sometimes acts like a wave and at other times acts as if it is made up of particles.

Note: Knowing Planck's constant sets the scale of energy for events in which the atom and subatomic particles take part.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
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Encyclopedia Article for plancks constant

## Planck's constant

(symbol h), fundamental physical constant characteristic of the mathematical formulations of quantum mechanics, which describes the behaviour of particles and waves on the atomic scale, including the particle aspect of light. The German physicist Max Planck introduced the constant in 1900 in his accurate formulation of the distribution of the radiation emitted by a blackbody, or perfect absorber of radiant energy (see Planck's radiation law). The significance of Planck's constant in this context is that radiation, such as light, is emitted, transmitted, and absorbed in discrete energy packets, or quanta, determined by the frequency of the radiation and the value of Planck's constant. The energy E of each quantum, or each photon, equals Planck's constant h times the radiation frequency symbolized by the Greek letter nu, nu, or simply E=hnu. A modified form of Planck's constant called h-bar (), or Dirac h, frequently appears in the formulations of quantum mechanics, in which equals h divided by 2pi.