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Permeability (electromagnetism)In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. Magnetic permeability is represented by the Greek letter μ. The term was coined in September, 1885 by Oliver Heaviside. Additional recommended knowledgeIn SI units, permeability is measured in henries per metre, or newtons per ampere squared. The constant value μ_{0} is known as the magnetic constant or the permeability of vacuum, and has the exact or defined value μ_{0} = 4π×10^{−7} N·A^{−2}. Relative permeabilityRelative permeability, sometimes denoted by the symbol μ_{r}, is the ratio of the permeability of a specific medium to the permeability of free space μ_{0}: In terms of relative permeability, the magnetic susceptibility is: χ_{m}, a dimensionless quantity, is sometimes called volumetric or bulk susceptibility, to distinguish it from χ_{p} (magnetic mass or specific susceptibility) and χ_{M} (molar or molar mass susceptibility).
Permeability varies with magnetic field. Values shown above are approximate and valid only at the magnetic fields shown. Moreover, they are given for a zero frequency; in practice, the permeability is generally a function of the frequency. When frequency is considered the permeability can be complex, corresponding to the in phase and out of phase response. Note that the magnetic permeability μ_{0} has an exact value in SI units (i.e. there is no error bar or uncertainty in its value), because the definition of ampere fixes its value to 4π × 10^{−7} H/m exactly. References
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Permeability_(electromagnetism)". A list of authors is available in Wikipedia. 