Permeability (electromagnetism)

In electromagnetism, permeability is the measure of magnetization made in a material reacting to an applied magnetic field. Permeability is often written as Greek letter μ and is the ratio of the magnetic induction B to the magnetizing field H in a material.

The term was coined by William Thomson, 1st Baron Kelvin in 1872, and used alongside permittivity by Oliver Heaviside in 1885. The permeability reciprocal is magnetic reluctivity.

In SI units, permeability is measured in henries per meter (H/m), or equivalently in newtons per ampere squared (N/A2). The permeability constant μ0, also known as the magnetic constant or the permeability of free space, is the proportionality between magnetic induction and magnetizing force when forming a magnetic field in a classical vacuum.

A closely related property of materials is magnetic susceptibility, which is a dimensionless proportionality factor that indicates the degree of magnetization of a material in response to an applied magnetic field.