Planck constant

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

h = 6.626 068 76(52) x 10-34 Js

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

ℏ = h / 2π = 1.054 571 596(82) x 10-34 Js

where π is Pi. This symbol is pronounced "h-bar", and uses the unicode symbol ℏ. Somewhat confusingly, ℏ is also referred to as "Planck's constant".

ℏ is the quantum of angular momentum. The angular momentum of any system, measured against any particular choice of axis, is always an integer multiple of this value. Therefore, ℏ is arguably the more fundamental (or at least useful) quantity.

See also:

• Electromagnetic radiation
• Schrödinger's equation
• Heisenberg's uncertainty principle
• Wave-Particle duality