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quantum theory

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A theory of physics in which energy exists only in discrete quantities, called quanta. It was originated in 1900 by the German physicist Max Karl Ernst Ludwig Planck (1858–1947), who suggested that electromagnetic radiation is quantized, i.e. it can be emitted or absorbed only in tiny packets, not continuously. Each quantum of radiation, called a photon, has an energy equal to hf, where h is the Planck constant and f the frequency of the radiation. This enabled Planck to explain the wavelength distribution of energy from hot bodies, known as black-body radiation. Quantum theory led to the modern theory of the interaction between matter and radiation known as quantum mechanics.

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