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Definition: photoelectric effect from Dictionary of Energy

Physics. a phenomenon in which electrons are emitted from a material (generally a metal) when it is exposed to light with a given frequency. The classical concept of light as a continuous wave could not account for this, and it was then explained by Einstein (1905) on the basis that light is a stream of separate particles. This interpretation, and his subsequent elaboration of it, formed the basis for much of quantum mechanics.

Summary Article: photoelectric effect from The Columbia Encyclopedia

emission of electrons by substances, especially metals, when light falls on their surfaces. The effect was discovered by H. R. Hertz in 1887. The failure of the classical theory of electromagnetic radiation to explain it helped lead to the development of the quantum theory. According to classical theory, when light, thought to be composed of waves, strikes substances, the energy of the liberated electrons ought to be proportional to the intensity of light. Experiments showed that, although the electron current produced depends upon the intensity of the light, the maximum energy of the electrons was not dependent on the intensity. Moreover, classical theory predicted that the photoelectric current should not depend on the frequency of the light and that there should be a time lag between the reception of light on the surface and the emission of the electrons. Neither of these predictions was borne out by experiment. In 1905, Albert Einstein published a theory that successfully explained the photoelectric effect. It was closely related to Planck's theory of blackbody radiation announced in 1900. According to Einstein's theory, the incident light is composed of discrete particles of energy, or quanta, called photons, the energy of each photon being proportional to its frequency according to the equation E=hυ, where E is the energy, υ is the frequency, and h is Planck's constant. Each photoelectron ejected is the result of the absorption of one photon. The maximum kinetic energy, KE, that any photoelectron can possess is given by KE = hυ-W, where W is the work function, i.e., the energy required to free an electron from the material, varying with the particular material. The effect has a number of practical applications, most based on the photoelectric cell.

The Columbia Encyclopedia, © Columbia University Press 2017

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