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Fr.: domaine magnétique
Any of several microscopic areas in a → ferromagnetic material that possesses a net → magnetic field, because electron spins are aligned in the same direction. In the absence of an external magnetic field, the directions of the magnetization vectors of the separate domains do not coincide and the resultant magnetization of the whole body may be zero.
Fr.: énergie magnétique
The energy stored in a magnetic field. It is the → work that must be done to establish a magnetic field in terms of the → magnetic induction. Magnetic energy varies as the square of the magnetic induction. It can be expressed in several other ways, for example in terms of the current and of the magnetic flux, or in terms of the current density and vector potential.
meydân-e meqnâtisi (#)
Fr.: champ magnétique
A field of force that is generated by electric currents, or, equivalently, a region in which magnetic forces can be observed.
magnetic field line
xatt-e meydân-e meqnâtisi (#)
Fr.: ligne de champ magnétique
An imaginary line used for representing the strength and direction of a magnetic field. Charged particles move freely along magnetic field lines, but are inhibited by the magnetic force from moving across field lines.
magnetic field strength
zur-e meydân-e meqnâtisi
Fr.: intensité du champs magnétique
Same as → magnetic intensity.
šâr-e meqnâtisi (#)
Fr.: flux magnétique
A measure of the quantity of magnetism or magnetic field. It is the number of lines of force passing normally through a given area. Magnetic flux is a scalar quantity defined as the surface integral of the → magnetic flux density. It is usually denoted by the Greek letter Φ and its SI unit is the → weber.
magnetic flux density
cagâli-ye šâr-e meqnâtisi (#)
Fr.: densité du flux magnétique
A vector quantity measuring the strength and direction of the magnetic field. It is the → magnetic flux per unit area of a magnetic field at right angles to the magnetic force. Magnetic flux density is expressed in → teslas. Also called → magnetic induction.
Fr.: hélicité magnétique
A quantity that measures the extent to which the magnetic field lines wrap and coil around each other. It is closely related to field line topology. Magnetic helicity is defined by: HM = ∫ A . B dV, where A is the vector potential of the magnetic field and the integration is over a volume V. → helicity; → kinetic helicity
Fr.: inclinaison magnétique
Fr.: induction magnétique
1) Same as → magnetic flux density.
Fr.: intensité magnétique
Strength of a magnetic field at a point, denoted H. The force which could be exerted on unit north magnetic pole situated at that point. Measured in oersteds. Same as → magnetic field strength.
magnetic massive star
setâre-ye porjerm-e meqnâtisi
Fr.: étoile massive magnétique
A → stellar magnetic field associated with
a → massive star.
Magnetic fields are detected only for seven to ten percent of all
studied massive → OB stars, and the
magnetic field occurrence does not depend on the
→ spectral type. Because
these magnetic fields seem to be stable over long time-scales and their
strength does not seem to correlate with known stellar properties, it
is assumed that they are of fossil origin
(→ fossil magnetic field)
and are frozen into the → radiative envelope
of the stars.
The fields are those of the birth
→ molecular clouds, partly trapped inside
the → pre-main sequence star
during the cloud → collapse
phase, possibly further enhanced by a
→ dynamo effect in the early fully convective
Typically, the polar field strength ranges from about a
hundred → Gauss up to several kiloGauss.
However, some weaker fields,
below 100 G, have recently been detected.
Fr.: méridien magnétique
A meridian passing through the Earth's → magnetic poles.
gaštâvar-e meqnâtisi (#)
Fr.: moment magnétique
1) A measure of the strength of a magnet or current-carrying coil. In the case of
a bar magnet it is obtained by multiplying the distance between the two
magnetic poles by the average strength of the poles. Same as
→ magnetic dipole moment
See also → dipole 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.
Fr.: aiguille aimantée
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.
magnetic null point
noqte-ye nul-e meqnâtisi
Fr.: point nul magnétique
tarâvâyi-ye meqnâtisi (#)
Fr.: perméabilité magnétique
The ratio of the → magnetic induction, B, in the substance to the external magnetic field, H, causing the → induction: μ = B/H. It is measured in henry/meter and is known as absolute permeability. The relative permeability is equal to the ratio of absolute permeability to the permeability of the free space. Thus μr = μ/μ0, where μ0, the permeability of free space has the value 4π x 10-7 henry/meter.