Gauss's law for electricity
qânun-e Gauss dar barq
Fr.: loi de Gauss en électricité
The total electric flux ψ out of an arbitrary closed surface in free space is equal to the net charge within the surface divided by the → permittivity. In differential form: ∇ . E = ρ/ε0, where ρ is the → charge density and ε0 the permittivity. The integral form of the law: ∫E . dS = Q/ε0 (closed surface integral). This is one of the four → Maxwell's equations.
induced electric field
meydân-e barqi-ye darhâzidé, ~ ~ darhâxté
Fr.: champ électric induit
An electric field created by the variation of a magnetic field. The induced electric field lines are usually perpendicular to the changing magnetic field that produces them.
internal photoelectric effect
oskar-e šid-barqi-ye daruni
Fr.: effet photoélectrique interne
The → photoelectric effect whereby photons absorbed by a solid (→ semiconductor) raise electrons from a lower to a higher → energy level (from → valence band to → conduction band). See also → external photoelectric effect.
linear electric quadrupole
cahârqotbe-ye barqi-ye xatti
Fr.: quadrupôle électrique linéaire
A system of three charges +q, -2q, and +q, arranged along a line to form an axial quadrupole. The → electric potential V due to a linear quadrupole varies as 1/r3, whereas the → electric intensity E varies as 1/r4.
Pertaining to electronic or other electrical effects that are due to the action of electromagnetic radiation, especially visible light.
Fr.: courant photoélectrique
oskar-e šid-barqi, ~ nur-barqi
Fr.: 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.
Fr.: 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 <hν < 13.6 eV, expel electrons from → interstellar dust grains and the excess → kinetic energy of the electrons is converted into gas → thermal energy through → collisions. The high energy limit corresponds to the cut-off in the → far-ultraviolet (FUV) radiation field caused by the hydrogen absorption (hν = 13.6 eV), while the low energy limit corresponds to the energy needed to free electrons from the grains (hν ~ 6 eV). In the cold neutral medium (Tkin≥ 200 K) photoelectric heating accounts for most of the heating, the → X-ray and → cosmic ray heating rates (→ cosmic-ray ionization) being more than an order of magnitude smaller. In a relatively dense neutral medium (nH≥ 100 cm-3), where a significant fraction of carbon is in the neutral form, carbon ionization becomes an important heating source, but it is still not comparable to the photoelectric effect. The heating rate cannot be directly measured, but it can be estimated through observations of the [C II] line emission, since this is believed to be the main → coolant in regions where the photoelectric heating is dominant (See, e.g., Juvela et al., 2003, arXiv:astro-ph/0302365).
borz-e šidsanjik, ~ nursanjik
Fr.: magnitude photoélectrique
The magnitude of an object as measured with a photoelectric photometer.
Fr.: photométrie photoélectrique
A photometry in which the magnitudes are obtained using a photoelectric photometer.
Fr.: effet piézoélectrique
The property exhibited by some crystals (notably quartz) that develop an electric charge or potential difference across them when subjected to mechanical strain; and conversely produce mechanical forces when a voltage is applied to them in a suitable manner.
Of, relating to, or produced by electric phenomena occurring in conjunction with a flow of heat.
Fr.: effet thermo-électrique
The electricity produced by heat or temperature difference in a conductor.