Reluctance

Magnetic reluctance is the resistance of a material to a magnetic field. It is defined as the ratio of magnetomotive force to magnetic flux. The term was coined in May 1888 by Oliver Heaviside.

Related Topics:
Magnetic field - Magnetomotive force - Magnetic flux - 1888 - Oliver Heaviside

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The definition can be expressed as:

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:S=rac{F}{Phi}

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where

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:S is the reluctance in ampere-turns per weber (a unit that is equivalent to turns per henry)

Related Topics:
Ampere - Weber - Henry

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:F is the magnetomotive force in ampere-turns

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:Φ is the magnetic flux in weber

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The reluctance of a uniform magnetic circuit can be calculated as:

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:S = rac{l}{mu_0 mu_r A}

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where

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:l is the length of the circuit in metres

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:mu_0 is the permeability of free space, equal to 4 pi imes 10^{-7} henry per metre

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:mu_r is the relative magnetic permeability of the material (dimensionless)

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:A is the cross-sectional area of the circuit in square metres

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The inverse of reluctance is called permeance.

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