Relative permeability: Difference between revisions
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In [[physics]], in particular in [[magnetostatics]], the '''relative permeability''' is an intrinsic property of a magnetic material. It is usually denoted by μ<sub>r</sub>. For simple magnetic materials, using [[SI units]], μ<sub>r</sub> is related to the proportionality constant between the [[magnetic flux density]] '''''B''''' and the [[magnetic field]] '''''H''''', namely '''''B''''' = {{nowrap|μ<sub>r</sub> μ<sub>0</sub> '''''H''''',}} where μ<sub>0</sub> is the [[magnetic constant]]. The relative permeability describes the ease by which a magnetic medium may be magnetized. | In [[physics]], in particular in [[magnetostatics]], the '''relative permeability''' is an intrinsic property of a magnetic material. It is usually denoted by μ<sub>r</sub>. For simple magnetic materials, using [[SI units]], μ<sub>r</sub> is related to the proportionality constant between the [[magnetic flux density]] '''''B''''' and the [[magnetic field]] '''''H''''', namely '''''B''''' = {{nowrap|μ<sub>r</sub> μ<sub>0</sub> '''''H''''',}} where μ<sub>0</sub> is the [[magnetic constant]]. The relative permeability describes the ease by which a magnetic medium may be magnetized. | ||
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For simple media, if μ<sub>r</sub> < 1, the medium is termed ''diamagnetic''; if > 1 ''paramagnetic''. Only [[classical vacuum]] has μ<sub>r</sub> = 1 (exact). It should be noted that the use of a constant as the relative permeability of a substance is an approximation, even for [[Vacuum (quantum electrodynamic)|quantum vacuum]]. A more complete representation recognizes that all media exhibit departures from this approximation, in particular, a dependence on field strength, a dependence upon the rate of variation of the field in both time and space, and a dependence upon the direction of the field. In many materials these dependencies are slight; in others, like [[Ferromagnetism|ferromagnets]], they are pronounced. | For simple media, if μ<sub>r</sub> < 1, the medium is termed ''diamagnetic''; if > 1 ''paramagnetic''. Only [[classical vacuum]] has μ<sub>r</sub> = 1 (exact). It should be noted that the use of a constant as the relative permeability of a substance is an approximation, even for [[Vacuum (quantum electrodynamic)|quantum vacuum]]. A more complete representation recognizes that all media exhibit departures from this approximation, in particular, a dependence on field strength, a dependence upon the rate of variation of the field in both time and space, and a dependence upon the direction of the field. In many materials these dependencies are slight; in others, like [[Ferromagnetism|ferromagnets]], they are pronounced. | ||
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Revision as of 11:00, 17 April 2011
In physics, in particular in magnetostatics, the relative permeability is an intrinsic property of a magnetic material. It is usually denoted by μr. For simple magnetic materials, using SI units, μr is related to the proportionality constant between the magnetic flux density B and the magnetic field H, namely B = μr μ0 H, where μ0 is the magnetic constant. The relative permeability describes the ease by which a magnetic medium may be magnetized.
A related quantity is the magnetic susceptibility, related to the magnetic permeability in cgs units by:
and in SI units by:
where μ0 is the magnetic constant.
The force exerted between two long parallel wires conducting a current and separated by a magnetizable medium, the magnetostatic force between the wires is changed by a factor μr. Empirically it is observed that the force may increase or decreases due to the presence of the magnetic medium, hence the relative permittivity μr may be greater than or less than 1.
For simple media, if μr < 1, the medium is termed diamagnetic; if > 1 paramagnetic. Only classical vacuum has μr = 1 (exact). It should be noted that the use of a constant as the relative permeability of a substance is an approximation, even for quantum vacuum. A more complete representation recognizes that all media exhibit departures from this approximation, in particular, a dependence on field strength, a dependence upon the rate of variation of the field in both time and space, and a dependence upon the direction of the field. In many materials these dependencies are slight; in others, like ferromagnets, they are pronounced.