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.
References in periodicals archive ?
Several teams are using different techniques to zero in on the Planck constant (SN: 9/5/15, p.
Fundamental particles have "inherent" number of spin, equal to integral or half-integral number (in Planck constant units), which never changes.
These are the ground state hyperfine splitting frequency of the cesium 133 atom [DELTA]v[([.sup.133]Cs).sub.hfs]; the speed of light in vacuum c; the Planck constant h; the elementary charge e (charge of a proton); the Boltzmann constant k; the Avogadro constant [N.sub.A], and the luminous efficacy [K.sub.cd] of monochromatic radiation of frequency 540 x [10.sup.12] hertz.
21 PHYSICAL REVIEW LETTERS, the NIST group gives a new value for the Planck constant of 6.62606891 X [10.sup.-34] Joule-seconds, with an uncertainty of 87 parts per billion, less than half the uncertainty of prior measurements.
The electron's angular momentum is always equal to the reduced Planck constant. This implies that the electron's mass has to increase [gamma] times in order to compensate for the decrease in its rotational velocity:
The energy values and the neutron wave functions in such a system depend on m, g, on the Planck constant and on the quantum number n only.
Kibble at England's National Physical Laboratory, this method offers a precise value of the Planck constant, from which one derives Avogadro's number.
Table 1 shows the basic set of electron and proton units that can be considered as a fundamental metrology (c is the speed of light in a vacuum, [??] is the Planck constant, [k.sub.B] is the Boltzmann constant).
The National Institute of Standards and Technology (NIST) watt balance experiment completed a determination of Planck constant in 1998 with a relative standard uncertainty of 87 X [10.sup.-9] (k = 1), concurrently with an upper limit on the drift rate of the SI kilogram mass standard.
Olsen, Accurate measurement of the Planck constant, Phys.
where [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] is the momentum operator and h is the reduced Planck constant, can be expressed using (2) as