An Etymological Dictionary of Astronomy and AstrophysicsEnglish-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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 photoelectric current   جریان ِ شید-برقی   jarayân-e šid-barqiFr.: courant photoélectrique   The current produced in an → photoelectric effect process when → photoelectrons are received at the positive electrode.→ photoelectric; → current. photoelectric effect   ا ُسکر ِ شید-برقی، ~ نور-برقی   oskar-e šid-barqi, ~ nur-barqiFr.: effet photoélectrique   The process of release of electrically charged particles (usually → electrons) as a result of irradiation of matter by light or other → electromagnetic radiation. The classical electromagnetic theory was unable to account for the following characteristics of the phenomenon. Light below a certain threshold frequency, no matter how intense, will not cause any electrons to be emitted. Light above that frequency, even if it is not very intense, will always cause electrons to be ejected. The electrons are ejected after some nanoseconds, independently of the light intensity. The maximum kinetic energy of the emitted electrons is a function of the frequency and does not dependent on the intensity of the incident light. The classical theory could not explain how a train of light waves spread out over a large number of atoms could, in a very short time interval, concentrate enough energy to knock a single electron out of the metal. In 1905, based on Planck's idea of → quanta, Einstein proposed that light consisted of quanta (later called → photons); that a given source could emit and absorb radiant energy only in units which are all exactly equal to the radiation frequency multiplied by a constant (→ Planck's constant); and that a photon with a frequency over a certain threshold would have sufficient energy to eject a single electron. His photoelectric equation is descibed as (1/2)mu2 = hν - A, where m is the electron mass, u is the electron velocity, h is Planck's constant, ν is the frequency, and A the → work function, which represents the amount of work needed by electrons to get free of the surface. See also → photoelectron, → photoelectric current, → external photoelectric effect, → internal photoelectric effect.→ photoelectric; → effect. photoelectric heating   گرمایش ِ شید-برقی   garmâyeš-e šid-barqiFr.: chauffage photoélectrique   A heating process occurring in → diffuse molecular clouds which is believed to be the main heating mechanism in cool → H I regions. Far-ultraviolet (FUV) photons, in the energy range 6 eV