# magnetic permeability

magnetic permeability
permeability (def. 2).

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Relative increase or decrease in the magnetic field inside a material compared with the magnetic field in which the material is located.

In empty space the magnetic permeability is 1, because there is no matter to modify the field. Materials may be classified by the value of their magnetic permeability. Diamagnetic materials (see diamagnetism) have constant relative permeabilities of slightly less than 1. Paramagnetic materials (see paramagnetism) have constant relative permeabilities of slightly more than 1. The relative permeability of ferromagnetic materials (see ferromagnetism) increases as the magnetizing field increases, reaches a maximum, and then decreases. Pure iron and some alloys have relative permeabilities of 100,000 or more.

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relative increase or decrease in the resultant magnetic field inside a material compared with the magnetizing field in which the given material is located; or the property of a material that is equal to the magnetic flux density B established within the material by a magnetizing field divided by the magnetic field strength H of the magnetizing field. Magnetic permeability μ (Greek mu) is thus defined as μ = B/H. Magnetic flux density B is a measure of the actual magnetic field within a material considered as a concentration of magnetic field lines, or flux, per unit cross-sectional area. Magnetic field strength H is a measure of the magnetizing field produced by electric current flow in a coil of wire.

In empty, or free, space the magnetic flux density is the same as the magnetizing field because there is no matter to modify the field. In centimetre–gram–second (cgs) units, the permeability B/H of space is dimensionless and has a value of 1. In metre–kilogram–second (mks) and SI units, B and H have different dimensions, and the permeability of free space (symbolized μ0) is defined as equal to 4π × 10-7 weber per ampere-metre so that the mks unit of electric current may be the same as the practical unit, the ampere. In these systems the permeability, B/H, is called the absolute permeability μ of the medium. The relative permeability μr is then defined as the ratio μ/μ0, which is dimensionless and has the same numerical value as the permeability in the cgs system. Thus, the relative permeability of free space, or vacuum, is 1.

Materials may be classified magnetically on the basis of their permeabilities. A diamagnetic material has a constant relative permeability slightly less than 1. When a diamagnetic material, such as bismuth, is placed in a magnetic field, the external field is partly expelled, and the magnetic flux density within it is slightly reduced. A paramagnetic material has a constant relative permeability slightly more than 1. When a paramagnetic material, such as platinum, is placed in a magnetic field, it becomes slightly magnetized in the direction of the external field. A ferromagnetic material, such as iron, does not have a constant relative permeability. As the magnetizing field increases, the relative permeability increases, reaches a maximum, and then decreases. Purified iron and many magnetic alloys have maximum relative permeabilities of 100,000 or more.

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Universalium. 2010.

### Look at other dictionaries:

• Magnetic permeability — Permeability Per me*a*bil i*ty, n. [Cf. F. perm[ e]abilit[ e].] The quality or state of being permeable. [1913 Webster] {Magnetic permeability} (Physics), the specific capacity of a body for magnetic induction, or its conducting power for lines… …   The Collaborative International Dictionary of English

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• magnetic permeability — magnetinė skvarba statusas T sritis chemija apibrėžtis Magnetinės indukcijos ir magnetinio lauko vektorių santykis. atitikmenys: angl. magnetic permeability; permeability rus. магнитная проницаемость …   Chemijos terminų aiškinamasis žodynas

• magnetic permeability — magnetinė skvarba statusas T sritis Standartizacija ir metrologija apibrėžtis Dydis, išreiškiamas iš formulės: B = μH; čia μ – magnetinė skvarba, B – magnetinio srauto tankio vektorius, H – magnetinio lauko stiprio vektorius. atitikmenys: angl.… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

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• magnetic permeability tensor — magnetinės skvarbos tenzorius statusas T sritis fizika atitikmenys: angl. magnetic permeability tensor vok. magnetischer Durchlässigkeitstensor, m; magnetischer Permeabilitätstensor, m rus. тензор магнитной проницаемости, m pranc. tenseur de… …   Fizikos terminų žodynas

• magnetic permeability — noun : permeability 4 * * * permeability (def. 2) …   Useful english dictionary

• magnetic permeability — /mægˌnɛtɪk pɜmiəˈbɪləti/ (say mag.netik permeeuh biluhtee) noun a measure of the ratio of the magnetic flux density in a body to the external magnetic field which induces it …

• magnetic permeability — noun a measure of the magnetisation of a material in a magnetic field; symbol μ. Materials with values less than 1 are diamagnetic those above are paramagnetic …   Wiktionary