permeability (μ)

Also called magnetic permeability (symbol μ), the ratio of the magnetic flux density, B, in a substance to the external magnetic field strength, H, i.e.:

μ = B / H.

The permeability of free space, μ₀ is also called the magnetic constant and has the value 4π × 10^-7 H m^-1 in SI units. The relative permeability of a substance, μ_r, is given by μ / μ₀, and is therefore dimensionless.

Materials showing diamagnetism and paramagnetism have permeabilities just below free space value; materials showing ferromagmetism have permabilities a thousand times greater. A material with a particularly high permability is permalloy.

Related category

• ELECTRICITY AND MAGNETISM

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