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The vacuum magnetic permeability (variously vacuum permeability, permeability of free space, permeability of vacuum, magnetic constant) is the magnetic permeability in a classical vacuum. It is a physical constant, conventionally written as μ 0 (pronounced "mu nought" or "mu zero").
In SI units, permeability is measured in henries per meter (H/m), or equivalently in newtons per ampere squared (N/A 2). The permeability constant μ 0, 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.
The impedance of free space (that is, the wave impedance of a plane wave in free space) is equal to the product of the vacuum permeability μ 0 and the speed of light in vacuum c 0. Before 2019, the values of both these constants were taken to be exact (they were given in the definitions of the ampere and the metre respectively), and the value ...
By definition, a perfect vacuum has a relative permittivity of exactly 1 whereas at standard temperature and pressure, ... µ 0 is the vacuum permeability.
With the definition of m as the pole strength times the distance between the poles, this leads to τ = μ 0 m H sin θ, where μ 0 is a constant called the vacuum permeability, measuring 4π × 10 −7 V·s/(A·m) and θ is the angle between H and m.
In this definition, the magnetic dipole moment of a system is the negative gradient of its intrinsic energy, U int, with respect to external magnetic field: = ^ ^ ^. Generically, the intrinsic energy includes the self-field energy of the system plus the energy of the internal workings of the system.
Permeability (electromagnetism), the degree of magnetization of a material in response to a magnetic field Vacuum permeability, permeability of free space or magnetic constant, a physical constant, the value of magnetic permeability in a classical vacuum
The relation between the magnetizing field H and the magnetic field B can also be expressed as the magnetic permeability: = / or the relative permeability = /, where is the vacuum permeability. The permeability of ferromagnetic materials is not constant, but depends on H .