Permeability (electromagnetism)

Some substances, called ferromagnetic materials or ferromagnets, are naturally magnetic. They are not a large single natural magnet, but are composed of a large number of very small magnets working together called domains. Those domains are not always aligned, and often they act against each other to reduce the strength of the net magnetic field.

Related Topics:
Ferromagnetic - Ferromagnets - Magnetic - Domains

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If you put the ferromagnetic material into an externally applied magnetic field, those domains tend to line up, so that the sum of the field from the ferromagnet plus the applied magnetic field are stronger than the applied magnetic field alone.

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In electromagnetism, permeability is the degree of magnetisation of a material that responds linearly to an applied magnetic field. Magnetic permeability is represented by the symbol μ. In September of 1885, Oliver Heaviside coined this term.

Related Topics:
Electromagnetism - Magnetic field - μ - Oliver Heaviside

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In SI units, permeability is measured in henrys per metre. The constant value mu_0 , is known as the magnetic constant, or by the older term permeability of a vacuum (absolute permeability below).

Related Topics:
SI - Henry - Metre

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:Permeability in linear materials owes its existence to the approximation:

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: mathbf{M}=chi_mmathbf{H}

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: Where chi_m , is a dimensionless scalar called the magnetic susceptibility.

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:According to the definition of the auxiliary field, mathbf{H}

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mathbf{B}=mu_0 (mathbf{H}+mathbf{M})=mu_0 (1 + chi_m)mathbf{H}

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:mu=mu_0(1+ chi_m) ,

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:Thus mu = rac {B} {H} ,

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where

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μ is the permeability, measured in henries per metre

Related Topics:
Henries - Metre

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B is the magnetic flux density (also called the magnetic induction) in the material, measured in teslas

Related Topics:
Magnetic flux density - Magnetic induction - Teslas

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H is the magnetic field strength, measured in amperes per metre

Related Topics:
Ampere - Metre

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