Photon -- from Eric Weisstein's World of Physics

The basic unit ("quantum") of electromagnetic radiation (and therefore light), usually denoted . Photons were first postulated by Planck, Eric Weisstein's World of Biography whose measurements of the blackbody spectrum showed that electromagnetic radiation had to come in discrete units, which were dubbed "photons" by the chemist Gilbert Lewis in 1926 (Griffiths 1987, p. 15).

The energy of a photon of frequency is given by

where h is Planck's constant. Because the energy of photons is directly proportional Eric Weisstein's World of Math to their frequency, low-energy photons have low frequencies, while high-energy photons have high frequencies. Low-energy photons are called radio waves or microwaves, medium-energy photons are called light (or light waves, or visible light), high-energy photons are called X-rays, while those having higher energy still are called gamma rays.

Compton Effect, Compton Scattering, Cosmic Background Radiation, Electromagnetic Radiation, Free-Streaming Photons, Gamma Ray, Light, Microwave, Pair Production, Photino, Photoelectric Effect, Photomultiplier Tube, Poynting-Robertson Effect, Radio Wave, X-Ray

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