# Planck's constant

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## Planck's constant

(plängks), fundamental constant of the quantum theory**quantum theory,**

modern physical theory concerned with the emission and absorption of energy by matter and with the motion of material particles; the quantum theory and the theory of relativity together form the theoretical basis of modern physics.

**.....**Click the link for more information. . It is represented by the letter

*h*and has a value of 6.62607 × 10

^{−34}joule-second. The combination

*h*/2π, denoted by

*h*(called "h-bar"), occurs frequently.

## Planck's constant

A fundamental physical constant which represents the elementary quantum of action, action being defined as energy multiplied by time. Introduced by Max Planck in 1900, it has the value *h* = 6.6261 × 10^{-27} erg-second or 6.6261 × 10^{-34} joule-second. The symbol *ℏ*, sometimes called the Dirac *h*, is often used for convenience in physics to denote the quantity *h*/2π, where π = 3.1416….

As used by Planck in deriving his radiation law, *h* multiplied by the frequency of radiation represented a bundle of energy, that is, a quantum of energy. Radiant energy at any wavelength can occur only as multiples of this energy; thus energy is quantized. *See* Compton effect, Fundamental constants, Heat radiation, Quantum mechanics

*The Great Soviet Encyclopedia*(1979). It might be outdated or ideologically biased.

## Planck’s Constant

(the quantum of action), a fundamental physical constant that determines a broad range of physical phenomena characterized by discreteness of action. These phenomena are studied in quantum mechanics. Planck’s constant was introduced by M. Planck in 1900 in establishing the law of energy distribution in a blackbody radiation spectrum. The symbol for the constant is *h.*

The most accurate value for Planck’s constant has been obtained on the basis of the Josephson effect: *h* = (6.626176 ± 0.000036) × 10^{–34} joule-Hz^{–1} = (6.626176 ± 0.000036) × 10^{–27} erg-Hz^{–1}. The constant *ℏ* = *h/2π* = (1.0545887 ± 0. 0000057) × 10^{–27} erg-Hz^{–1}, which is more often used, is also called Planck’s constant.

## Planck's constant

[′pläŋks ‚kän·stənt]^{-34}joule-second. Symbolized

*h*. Also known as quantum of action.