Planck’s constant

[2] Planck’s constant (h) is a fundamental physical constant characteristic of the mathematical formulations of quantum mechanics, depicting particles and waves' behaviour on the atomic scale, including the light's particle aspect. German physicist Max (1900) Planck introduced the constant in his radiation distribution formulation emitted by a blackbody/perfect absorber of radiant energy (see Planck’s radiation law). This constant's significance in this context is that radiation (e.g., light) is emitted, transmitted, and absorbed in discrete energy packets (quanta), determined by the radiation's frequency and the Planck’s constant value.

Energy E per quantum/photon is the Planck’s constant h times radiation frequency (nu ν): E = hν. The reduced Planck’s constant (h-bar; ℏ) is a modified form in which ℏ equals h/2π, is angular momentum's quantization. E.g., An electron's angular momentum bound to an atomic nucleus is quantized and can only be a multiple of ℏ.

The Planck’s constant's dimension is energy and time's product, a quantity called action. Planck’s constant is often defined, thus as the action's elementary quantum. Its value in metre-kilogram-second units is defined as 6.62607015 × 10−34 joule second.