# Planck constant

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## Planck constant

(plank) Symbol: h . A fundamental constant with the value 6.626 076 × 10–34 joule seconds. According to quantum theory, electromagnetic radiation has a dual nature. Although many phenomena, including reflection and refraction, can be explained in terms of the wavelike nature of radiation, radiation may also be considered to be composed of discrete packets of energy called photons, so that it acts as a stream of particles. The particle-like and wavelike properties are related by Planck's law, in which the Planck constant is the constant of proportionality:
E = hv = hc
E is the energy of the photons and v and λ the frequency and wavelength of the wave; c is the speed of light in a vacuum. The Planck constant appears in most equations of quantum theory and quantum mechanics, including Planck's radiation law for black bodies.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
References in periodicals archive ?
Like the other electron models discussed above, the Helical Solenoid Electron Model postulates that the tangential velocity of the electric charge matches the speed of light and that the electron's angular momentum matches the reduced Planck constant.
where c is the speed of light, [??] is the reduced Planck constant, and m is the electron mass.
Since the product of the mass of two point masses 2[delta]m, the speed v, and the radius of the doublet r is given by; 2[delta]mcr = [delta]mcd, where d = 2r; has the units of energy and time (or that of angular momentum) and is the same as that of the Planck's constant, we conclude that a limit must be placed on the smallest allowable doublet, giving [delta]m d = [??]/c, where [??] is the reduced Planck constant. This also suggests that ([delta]md) is a new fundamental physical unit involving mass and distance combined together (= 3.5177 x [10.sup.-43] kg m).

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