jan 17, 1905 - Albert Einstein - Photons, Photoelectric Effect, and Quantum Theory(1905)

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In 1905, Einstein published a paper called "On a Heuristic Viewpoint Concerning the Production and Transformation of Light" which explained the photoelectric effect. He stated that light particles hitting a metal surface at certain frequencies cause electrons to be shot out by the atoms which the metal is composed of. Einstein's paper was heavily influenced by previous ideas presented by Max Planck. However, the term "photon" wasn't used until 1929 by Gilbert Lewis. Einstein also expanded on Planck's ideas on quantum theory by discovering that radiation was also quantized.

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