Originally posted by sucahyo
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Wikipedia:
In 1900, Max Planck was working on black-body radiation and suggested that the energy in electromagnetic waves could only be released in "packets" of energy; he called these quanta (singular quantum).
Later, in 1905 Albert Einstein went further by suggesting that EM waves could only exist in these discrete wave-packets. He called such a wave-packet the light quantum (German: das Lichtquant). The name photon derives from the Greek word for light, φως (transliterated phôs), and was coined in 1926 by the physical chemist Gilbert Lewis, who published a speculative theory in which photons were "uncreatable and indestructible".
Individual photons can be detected by several methods. In the classic photomultiplier tube (1887 Heinrich Hertz), a photon landing on a metal plate ejects an electron, initiating an ever-amplifying avalanche of electrons. Microchips use a similar effect in semiconductors: an incident photon generates a charge on a microscopic capacitor that can be detected.
Other detectors such as Geiger counters use the ability of photons to ionize gas molecules, causing a detectable change in conductivity.
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