Planck's constant

2021-06-06T14:39:02Z

ScienceTrueSeeker: added ca year Planck introduced the Planck constant

'''Planck's constant''', denoted <math>h</math>, is a fundamental constant in [[physics]]. The current value of '''Planck's constant''' is <math>6.626070040(81) \times 10^{-34}</math> Joule-seconds (numbers in brackets represent uncertainty in the last two decimal places).<ref>http://physics.nist.gov/cgi-bin/cuu/Value?h</ref>

==History==

It was first used by [[Max Planck]] around 1900 to explain the radiation curves of black-bodies. He supposed that [[light]] could be modelled as a series of particles (now called [[photons]]), each with an [[energy]] proportional to its frequnecy, <math>\nu</math>. The constant of proportionality was Planck's constant. Mathematically this can be expressed as:

<math>E = h \nu</math>

In 1924, Louis De Broglie proposed [[Wave-particle duality]], the idea that matter ([[proton]]s and [[electron]]s for example) had a wave-like nature.<ref>https://www.nobelprize.org/nobel_prizes/physics/laureates/1929/broglie-bio.html</ref> Here too, is Planck's constant:

<math>\lambda = \frac{h}{p} </math>

where
:<math>\lambda</math> is the [[wavelength]] of the particle
:<math>p</math> is the [[momentum]] of the particle

The Planck constant also occurs in equations fundamental to [[quantum mechanics]], such as the [[Schrodinger equation]].

==Reduced Planck's Constant==

Planck's constant often occurs in equations with the mathematical constant <math>\pi</math>. As such, a factor of <math>\frac{1}{2 \pi}</math> may be taken into Planck's constant as

<math>\hbar = \frac{h}{2 \pi}</math>

The resulting constant is pronounced "h-bar".

==See also==
*[[Quantum mechanics]]
*[[Photon]]
*[[Schrodinger equation]]

==References==
{{Reflist}}

[[Category:Physics]]
[[Category:Quantum Mechanics]]

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Planck's constant