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.
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
magnetic Prandtl number
adad-e Prandtl-e meqnâtisi
Fr.: nombre de Prandtl magnétique
A → dimensionless quantity used in → magnetohydrodynamics to describe the relative balance of → kinematic viscosity to → magnetic diffusion. It is described by: Pr = σμ0ν = ν/η, where σ is the → conductivity of the fluid, μ0 is the → magnetic permeability of the fluid, ν is the kinematic viscosity of the fluid, and η is the → magnetic diffusivity.
fešâr-e meqnâtisi (#)
Fr.: pression magnétique
The pressure exerted by a magnetic field on the material that contains the field.
magnetic quantum number
adad-e kuântomi-ye meqnâtisi (#)
Fr.: nombre quantique magnétique
In atomic physics, a quantum number that denotes the energy levels available within a subshell. Designated by the letter m, it is one of a set of quantum numbers which describe the unique quantum state of an electron.
Fr.: reconnexion magnétique
In a → plasma, a change of → magnetic connectivity of plasma elements due to the presence of a localized → diffusion region. It allows charged particles to move from one → magnetic field line to another. Magnetic reconnection is an important process transforming magnetic energy into heat or/and kinetic energy. Magnetic reconnection events occur in the Earth's → magnetosphere. The process plays an important role in explosive phenomena in the Sun, such as → coronal mass ejections and → solar flares which heat the → solar corona.
Fr.: relaxation magnétique
The process by which a magnetic system relaxes to its minimum energy state over time.
bâzâvâyi-ye meqnâtisi (#)
Fr.: résonance magnétique
A phenomenon exhibited by certain atoms whereby they absorb energy at specific (resonant) frequencies when subjected to alternating magnetic fields.
Fr.: inversion magnétique
A change in the Earth's → magnetic field in which the → magnetic north pole is transformed into a → magnetic south pole and the magnetic south pole becomes a magnetic north pole. There are geological proofs indicating that the Earth's magnetic field has undergone numerous reversals of → polarity in the past. In the last 10 million years, there have been, on average, 4 or 5 reversals per million years. At other times, for example during the → Cretaceous era, there have been much longer periods when no reversals occurred. Over the past two centuries, Earth's magnetic field has weakened by 15%. Risks of a weak magnetic field include more deaths from cancer due to increased radiation, electrical grid collapse from severe solar storms, climate change, and temporary ozone holes. See also → geomagnetic excursion.
magnetic Reynolds number
adad-e Reynolds-e meqnâtisi
Fr.: nombre de Reynolds magnétique
A → dimensionless quantity used in → magnetohydrodynamics to describe the relative balance of → magnetic advection to → magnetic diffusion. It is given by: Rm = σμ0νLU0, where σ is the → conductivity of the fluid, μ0 is the → magnetic permeability of the fluid, L is he characteristic length scale of the fluid flow, and U0 the characteristic velocity of the flow. A typical value for the Earth is Rm ~ 200.
Fr.: rigidité magnétique
In → plasma physics, a → quantity that describes the → resistance of a → charged particle to change its direction of motion under the influence of a perpendicular → magnetic field. Rigidity is defined as: R = rLBc = (pc)/(Ze), where rL is the → Larmor radius, B is → magnetic induction, c is the → speed of light, p is the → momentum of the particle, Z is → atomic number, and e the → electron charge. Since pc has the dimensions of energy and e the dimensions of charge, rigidity has the dimensions of → volts (a 10 GeV proton has a rigidity of 10 GV). In → cosmic ray studies, the energies of cosmic rays are often quoted in terms of their rigidities, rather than their energies per nucleon.
magnetic south pole
qotab-e daštar-e meqnâtisi
Fr.: pôle sud magnétique
Fr.: dédoublement magnétique
A process whereby the (internal) → magnetic field of a star modifies the → pulsations by lifting some of its degeneracy. Instead of just one pulsation frequency, a multiplet of frequencies is then observed. This effect was proposed as a possible explanation for the observed frequency pattern of → Beta Cephei. In practice, the magnetic splitting is difficult to observe, because of the very small expected frequency difference between the peaks. However, when unaccounted for, it may lead to a wrong mode identification. The current best candidate to detect magnetic splitting is → HD 43317, since this star displays two close frequency patterns (Buysschaert et al., 2017, astro-ph/1709.02619).
setâre-ye meqnâtisi (#)
Fr.: étoile magnétique
tufân-e meqnâtisi (#)
Fr.: orage magnétique
A temporary, worldwide disturbance of the Earth's magnetic field by streams of charged particles from the Sun. Magnetic storms are frequently characterized by a sudden onset, in which the magnetic field undergoes marked changes in the course of an hour or less, followed by a very gradual return to normalcy, which may take several days.
Fr.: susceptibilité magnétique
Fr.: bande magnétique
A continuous, flexible ribbon impregnated or coated with magnetic-sensitive material on which information (sound, images, data, etc.) may be recorded.
Fr.: tension magnétique
In → magnetohydrodynamic (MHD) treatment of → plasmas, that component of the → Lorentz force which is directed toward the centre of curvature of the → magnetic field lines and thus acts to straighten out the field lines. The Lorentz force can be decomposed into two components orthogonal to the magnetic field: j× B = (B . ∇) B / μ0 - ∇ (B2 / 2μ0), where j is the → current density, μ0 is the → magnetic permeability of free space, and B is the → magnetic flux density. The left side term is the Lorentz force, the first term on the right side is the magnetic tension and the second term the → magnetic pressure.