qotb-e âsmân (#)
Fr.: pole céleste
The point of the sky, north or south, where the projection of the Earth's axis of rotation intersects the → celestial sphere. They are at 90° relative to the → celestial equator. Because of → precession, the celestial poles describe a circle around the ecliptic's poles every 25,800 years.
1) A combination of two electrically or magnetically charged
particles of opposite signs, which are separated by a very small
nâhamsângardi-ye dipol, ~ diqotbé
Fr.: anisotropie dipolaire
A form of anistropy in the temperature of the → cosmic microwave background radiation, appearing as one hot pole and one cold pole, caused by our motion with respect to the cosmic background radiation. The temperature variations, amounting to 1 part in 1000, yield a velocity of about 600 km/sec for our Galaxy with respect to the background. → cosmic microwave background anisotropy.
→ dipole; → anisotropy.
ânten-e dipol, ~ diqotbé
Fr.: antenne dipôle
One of the simplest kinds of antenna which is connected at the center to a radio-frequency feed line for transmitting or receiving radio frequency energy. It differs from the dish antenna in that it consists of many separate antennas that collect energy by feeding all their weak individual signals into one common receiving set.
gaštâvar-e doqotbé (#)
Fr.: moment dipolaire
1) The product of the strength of either of the charges in an
→ electric dipole and the distance separating the two charges.
It is expressed in → coulomb meters. Dipole moment is a
→ vector quantity.
Its direction is defined as toward the positive charge. In chemistry dipole moment is
a quantitative measure of polarity in a molecule;
the unit is the → debye.
Fr.: rayonnement dipolaire
The electromagnetic radiation produced by an oscillating → electric dipole or → magnetic dipole.
Fr.: pole de l'écliptique
Either of the two points on the celestial sphere that are 90° above and below the plane of ecliptic. The north ecliptic pole lies in → Draco, and the south ecliptic pole in → Dorado. Due to → precession, the → celestial pole moves in a circle around the ecliptic poles once every 25,800 years.
dipol-e barqi, diqotbe-ye ~
Fr.: dipôle électrique
1) A type of → charge distribution
consisting of two charges, a
positive and a negative charge of the same magnitude separated by a
distance s, which is small compared to the distance r to
the point P at which the → electric potential
is V and the → electric field
intensity is E.The potential falls as the
square of the distance (1/r2) and the electric
field intensity decreases as
the cube of the distance (1/r3).
Fr.: multipôle électrique
An electric → charge distribution consisting of more than four → positive and → negative → electric charges located at a small distance from each other. The multipole concept is an extension of the → electric quadrupole. For the generalized multipole characterized by the letter l, the potential at a distance r varies as 1/rl + 1 and the field intensity as 1/rl + 2.
Fr.: pôle galactique
The point on the sky, north or south, at which the galaxy's rotation axis would meet the celestial sphere.
Fr.: pôle géodésique
Any of the interaction points of the axis of revolution of the → reference ellipsoid with its surface.
geographic north pole
qotb-e hudar-e zaminnegârik
Fr.: pôle nord géographique
→ north pole.
→ geographic; → north; → pole.
geographic south pole
qotb-e daštar-e zaminnegârik
Fr.: pôle sud géographique
→ south pole.
→ geographic; → south; → pole.
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.
→ linear; → electric; → quadrupole.
Fr.: dipole magnétique
A system that generates a → magnetic field in which the field is considered to result from two opposite poles, as in the north and south poles of a magnet, much as an → electric field originates from a positive and a negative charge in an → electric dipole. A loop carrying an electric current also acts as a magnetic dipole. Magnetic dipoles experience a torque in the presence of magnetic fields. → dipole moment; → magnetic moment.
magnetic dipole moment
gaštâvar-e doqotbe-ye meqnâtisi
Fr.: moment dipolaire magnétique
Same as → magnetic moment.
takqotbe-ye meqnâtisi (#)
Fr.: monopôle magnétique
A hypothetical particle that carries a single → magnetic pole, in contrast to magnets which are north-south pole pairs. These massive particles (billions of times heavier than the → proton) are required by grand unified theories(→ GUTs) to explain the actual matter content of the Universe, particularly the dominance of matter upon → antimatter. However, their existence contradicts → Gauss's law for magnetism.
magnetic monopole problem
parâse-ye takqotbe-ye meqnâtisi
Fr.: problème du monopôle magnétique
A problem concerning the compatibility of grand unified theories (→ GUTs) with standard cosmology. If standard cosmology was combined with grand unified theories, far too many → magnetic monopoles would have been produced in the early Universe. The → inflation hypothesis aims at explaining the observed scarcity of monopoles. The inflation has deceased their density by a huge factor.
magnetic north pole
qotab-e hudar-e meqnâtisi
Fr.: pôle nord magnétique
A point of the → magnetosphere where the Earth's → magnetic field points vertically downward; in other words it has a 90° → magnetic dip toward the Earth's surface. The magnetic north pole can also be defined as the point toward which the south pole of the → compass needle is directed. The magnetic north pole is different from the → geographic north pole. It is actually hundreds of kilometers south of the geographic north pole. However, this has not always been the case. In the past 150 years it has moved more than 1,000 kilometers. Every 200,000 to 300,000 years the magnetic field of the Earth reverses direction, → magnetic reversal. Since the Earth's magnetic field is not exactly symmetrical, the north and south magnetic poles are not → antipodal.
qotb-e meqnâtisi (#)
Fr.: pôle magnétique
1) The region of a magnet toward which the lines of magnetic force
converge (south pole) or from which the lines of force diverge