# Planck's constant

From AMS Glossary

## Planck's constant

A universal constant, denoted by

*h*, with the value 6.626075 x 10^{-34}J s, in the quantum theory of matter and radiation.Planck's constant is the bridge between the wave and particle descriptions of light, an electromagnetic wave of frequency ν alternatively described as a stream of photons each with energy Planck's constant is a fundamental scaling parameter of the universe, determining, among other things, the sizes of atoms and molecules.

*h*ν. According to the quantum theory, when the energy of an atom, molecule, or nucleus changes from one discrete energy level*E*_{1}to another*E*_{2}, conservation of energy requires the emission (creation) or absorption (annihilation) of a photon with energy given by the Einstein frequency condition