Glossary

Photon

A single quantum (particle) of light, carrying energy proportional to its frequency.

Image: Gpvos (Wikipedia). CC BY-SA 3.0, via Wikimedia Commons (Source)

A photon is the elementary particle of light and all electromagnetic radiation. It has no mass, always travels at the speed of light in a vacuum, and carries energy E = hf, where f is the frequency and h is Planck's constant.

Einstein's 1905 idea of light quanta, building on Max Planck's work, made the photon central to quantum physics and to technologies from solar cells to lasers.

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Source: Wikipedia: Photon — Read the full article on Wikipedia.

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