Planck constant

Planck constant

(plank) Symbol: h . A fundamental constant with the value 6.626 076 × 10^–34 joule seconds. According to quantum theory, electromagnetic radiation has a dual nature. Although many phenomena, including reflection and refraction, can be explained in terms of the wavelike nature of radiation, radiation may also be considered to be composed of discrete packets of energy called photons, so that it acts as a stream of particles. The particle-like and wavelike properties are related by Planck's law, in which the Planck constant is the constant of proportionality:

E = hv = hc /λ

E is the energy of the photons and v and λ the frequency and wavelength of the wave; c is the speed of light in a vacuum. The Planck constant appears in most equations of quantum theory and quantum mechanics, including Planck's radiation law for black bodies.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006