photoelectric effect (redirected from Hertz effect)

photoelectric effect, 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 black body 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=h&ugr;, where E is the energy, &ugr; 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 = h&ugr;−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.

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photoelectric effect

Phenomenon in which charged particles are released from a material when it absorbs radiant energy (see radiation). It is often thought of as the ejection of electrons from the surface of a metal plate when visible light falls on it. It can also occur if the radiation is in the wavelength range of ultraviolet radiation, X rays, or gamma rays. The emitting surface may be a solid, liquid, or gas, and the emitted particles may be electrons or ions. The effect was discovered in 1887 by Heinrich Hertz and explained by Albert Einstein in work for which he received the Nobel Prize.