In the late nineteenth century, it was discovered that a negatively charged, clean metal plate lost its electric charge when illuminated by ultraviolet light. Later, after Thomson’s discovery of the electron, it was recognized that the negative charge on the metal plate was due to an excess of electrons. These electrons absorbed energy from the electromagnetic field (ultraviolet radiation), increasing their kinetic energies sufficiently to break the bonds that held them and escape from the metal surface. This phenomenon in which electrons are ejected from metal as a result of light shined on the surface is known as the photoelectric effect. All metals exhibit this property. For some, it can be demonstrated with visible light.
KeywordsDust Mercury Chromium Lithium Cadmium
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