qânun-e Kirchhoff (#)
Fr.: loi de Kirchhoff
The radiation law which states that at thermal equilibrium the ratio of the energy emitted by a body to the energy absorbed by it depends only on the temperature of the body.
Gustav Robert Kirchhoff (1824-1887), a German physicist who made major contributions to the understanding of electric circuits, spectroscopy, and the emission of black-body radiation from heated objects; → law.
Fr.: nébuleuse de Kleinmann-Law
An strong, extended infrared source in the Orion Nebula, about 1 arcminute NW of the Trapezium and about 12 arcseconds south of the → Becklin-Neugebauer object. It dominates the infrared emission at wavelengths above 20 microns. It probably represents a cluster of young and forming stars embedded in a dusty molecular cloud.
Named after Douglas E. Kleinmann (1942-) and Frank J. Low (1933-), who first studied this object in 1967; → nebula.
qânun-e Kramers (#)
Fr.: loi de Kramers
An approximate expression for deriving the → opacity that depends upon temperature with a power law: κ ∝ ρT-3.5, where ρ represents the density. In → partial ionization zones, a part of the energy released during a layer's compression can be used for further ionization, rather than raising the temperature of the gas. As the temperature of the compressed layer has not substantially increased, the increase in density produces a corresponding increase in the opacity of the layer. Likewise, during the expansion phase, the temperature does not decrease significantly since the ions release energy when they recombine with electrons.
Derived in 1923 by the Dutch physicist Henrik Kramers (1894-1952); → law.
Kramers' opacity law
qânun-e kederi-ye Kramers (#)
Fr.: loi de l'opacité de Kramers
Same as → Kramers' law.
Named after Henrik Kramers (1894-1952); → law.
Lambert's cosine law
qânun-e cosinus-e Lambert
Fr.: loi en cosinus de Lambert
The intensity of the light emanating in any given direction from a perfectly diffusing surface is proportional to the cosine of the angle between the direction and the normal to the surface. Also called → Lambert's law.
Fr.: loi de Lambert
Same as → Lambert's cosine law.
qânun (#), arté (#)
1) A rule of conduct or procedure established by custom, agreement,
M.E., O.E. lagu, from O.N. *lagu, variant of lag "that which is laid down;" cf. Ger. liegen, E. lay, lie; PIE *legh- "To lie, lay;" compare with Hittite laggari "falls, lies," Gk. lekhesthai "to lie down," L. lectus "bed," O.Ir. lige "bed, tomb," Tokharian lake, leke "bed."
Qânun, from Ar., ultimately from Gk. kanon "rule."
law of cosines
Fr.: loi des cosinus
An expression that for any triangle relates the length of a side to the cosine of the opposite angle and the lengths of the two other sides. If a, b, and c are the sides and A, B, and C are the corresponding opposites angles: a2 = b2 + c2 - 2bc cos A; b2 = c2 + a2 - 2ca cos B; c2 = a2 + b2 - 2ab cos C.
law of excluded middle
qânun-e miyâni soklândé
Fr.: principe du milieu exclu
Same as → principle of excluded middle.
law of identity
Fr.: principe d'identité
Same as → principle of identity.
law of inertia
qânun-e laxti (#)
Fr.: loi d'inertie
law of non-contradiction
Fr.: principe de non-contradiction
Same as → principle of non-contradiction.
law of reflection
qânun-e bâztâb (#)
Fr.: loi de réflexion
One of the two laws governing reflection of light from a surface: a) The → incident ray, normal to surface, and reflected ray lie in the same plane. b) The → angle of incidence (with the normal to the surface) is equal to the → angle of reflection.
law of refraction
qânun-e šekast (#)
Fr.: loi de réfraction
One of the two laws governing → refraction of light when it enters another transparent medium: a) The → incident ray, normal to the surface, and refracted ray, all lie in the same plane. b) → Snell's law is satisfied.
law of sines
Fr.: loi des sinus
In any triangle the sides are proportional to the sines of the opposite angles: a/sin A = b/sin B = c/sin C, where A, B, and C are the three vertices and a, b, and c are the corresponding sides.
An artificially produced → radioactive→ chemical element; symbol Lr (formerly Lw). → Atomic number 103; → atomic weight of most stable isotope 262; → melting point about 1,627°C; → boiling point and → specific gravity unknown; → valence +3. The longest half-life associated with this unstable element is 3.6 hour 262Lr. Credit for the first synthesis of this element in 1971 is given jointly to American chemists from the University of California laboratory in Berkeley under Albert Ghiorso and the Russian team at the Joint Institute for Nuclear Reactions lab in Dubna, under Georgi N. Flerov.
laws of dynamics
Fr.: lois de dynamique
The three basic laws of → dynamics which were first formulated by Isaac Newton in his classical work "Mathematical Principles of Natural Philosophy" published in 1687. → Newton's first law of motion; → Newton's second law of motion; → Newton's third law of motion.
Fr.: loi de Leavitt
Same as the → period-luminosity relation.
qânun-e Lenz (#)
Fr.: loi de Lenz
The direction of an induced current is such as to oppose the cause producing it. The cause of the current may be the motion of a conductor in a magnetic field, or it may be the change of flux through a stationary circuit.
Named after Heinrich Friedrich Emil Lenz (1804-1865), German physicist, who published the law in 1834; → law.
qânun-e Malus (#)
Fr.: loi de Malus
If the light wave entering an → analyzer is → linearly polarized, the intensity of the wave emerging from the analyzer is I = k I0 cos2φ, where k is the coefficient of transmission of the analyzer, I0 is the intensity of the incident light, and φ is the angle between the planes of → polarization of the incident light and the light emerging from the analyzer.
Named after Etienne Louis Malus (1775-1812), French physicist who also discovered polarization by reflection at a glass surface (1808); → law.