# Planck's constant

Planck's constant
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.
[1905-10; named after M. K. E. PLANCK]

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(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 (Planck, Max) 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, ν, or simply E = hν. A modified form of Planck's constant called h-bar (ℏ), or Dirac h, frequently appears in the formulations of quantum mechanics, in which ℏ equals h divided by 2π.

The dimension of Planck's constant is the product of energy multiplied by time, a quantity called action. Planck's constant is often defined, therefore, as the elementary quantum of action. Its value in metre-kilogram-second units is 6.6260693 × 10−34 joule∙second, with a standard uncertainty of 0.0000011 × 10−34 joule∙second.

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Universalium. 2010.

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• Planck's constant — plaŋ(k)s , pläŋ(k)s n a constant that gives the unvarying ratio of the energy of a quantum of radiation to its frequency and that has an approximate value of 6.626 × 10 34 joule second symbol h Planck pläŋk Max Karl Ernst Ludwig (1858 1947)… …   Medical dictionary

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• Planck's constant — Planck s′ (or Planck′) con′stant n. phs a unit used in quantum mechanics that equals the ratio of the energy of a quantum of radiation to the frequency of the radiation, approximately 6.626 x 10 34 joule second Symbol: h • Etymology: 1905–10;… …   From formal English to slang

• planck's constant — Constant value (6.626 x 10 34 watt seconds squared) which, when multiplied by the frequency of radiation, determines the amount of energy in a photon …   Dictionary of automotive terms

• Planck's constant — n. (also Planck constant) a fundamental constant, equal to the energy of quanta of electromagnetic radiation divided by its frequency, with a value of 6.626 x 10( 34) joules. Etymology: M. Planck, Ger. physicist d. 1947 …   Useful english dictionary

• Planck's constant — noun Etymology: Max K. E. L. Planck Date: 1910 a constant that gives the unvarying ratio of the energy of a quantum of radiation to its frequency and that has an approximate value of 6.626 × 10 34 J•s symbol h …   New Collegiate Dictionary

• Planck's constant — noun Physics a fundamental constant relating the energy of a quantum of electromagnetic radiation to its frequency, equal to 6.626 × 10 34 joules. Origin early 20th cent.: named after the German physicist Max Planck …   English new terms dictionary

• Planck's constant — /ˈplæŋks kɒnstənt / (say plangks konstuhnt) noun Physics a universal constant (approx. 6.626 × 10 34 joule seconds) expressing the proportion of the energy of any form of wavelike radiation to its frequency. Symbol: h {named after Max Planck,… …

• Planck's constant — noun the constant of proportionality relating the energy and frequency of a photon (6.626 x 10 joule seconds); also related to the indeterminacy limit in the Heisenberg uncertainty principle …   Wiktionary