Planck's constant

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Planck's constant, denoted h, named after the physicist Max Planck, is a physical constant which appears in all quantum mechanical equations. Its value is approximately

h = 6.6261 × 10^-34 Js

Planck's constant can be seen as a conversion factor between frequency and energy, especially for photons. The unicode symbol ℎ (ℎ) can be used for Planck's constant.

The abbreviation

where π is Pi, is commonly encountered. It is pronounced as "h-bar". The constant is sometimes referred to as Dirac's constant after Paul Dirac (although hardly anyone calls it that; Ask an average physicist what a Dirac's constant is and you're liable to get a blank stare.). The unicode symbol ℏ (ℏ) can be used for this on some browsers.

is the quantum of angular momentum, including spin. The angular momentum of any system, measured against any particular choice of axis, is always an integer multiple of this value. also occurs in Heisenberg's uncertainty principle. It has therefore been argued that is more fundamental than h. is used to define the Planck units.

see also: Electromagnetic radiation, Schrödinger equation, Heisenberg's uncertainty principle, Wave-particle duality, Quantum Hall effect