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In another system, the "rationalized metre–kilogram–second (rmks) system" (or alternatively the "metre–kilogram–second–ampere (mksa) system"), k m is written as μ 0 /2π, where μ 0 is a measurement-system constant called the "magnetic constant". [b] The value of μ 0 was chosen such that the rmks unit of current is equal in size to ...
The permeability of vacuum (also known as permeability of free space) is a physical constant, denoted μ 0. The SI units of μ are volt-seconds per ampere-meter, equivalently henry per meter. Typically μ would be a scalar, but for an anisotropic material, μ could be a second rank tensor. However, inside strong magnetic materials (such as iron ...
In free space, where ε = ε 0 and μ = μ 0 are constant everywhere, Maxwell's equations simplify considerably once the language of differential geometry and differential forms is used. The electric and magnetic fields are now jointly described by a 2-form F in a 4-dimensional spacetime manifold.
where μ 0 is the vacuum permeability (see table of physical constants), and (1 + χ v) is the relative permeability of the material. Thus the volume magnetic susceptibility χ v and the magnetic permeability μ are related by the following formula: = (+).
The definitions for monopoles are of theoretical interest, although real magnetic dipoles can be described using pole strengths. There are two possible units for monopole strength, Wb (Weber) and A m (Ampere metre). Dimensional analysis shows that magnetic charges relate by q m (Wb) = μ 0 q m (Am).
(In addition ε 0 and μ 0 are overdetermined, because ε 0 μ 0 = 1 / c 2.) The below points are true in both Heaviside–Lorentz and Gaussian systems, but not SI. The electric and magnetic fields E and B have the same dimensions in the Heaviside–Lorentz system, meaning it is easy to recall where factors of c go in the Maxwell equation.
The two alternative definitions of the Poynting vector are equal in vacuum or in non-magnetic materials, where B = μ 0 H. In all other cases, they differ in that S = (1/ μ 0 ) E × B and the corresponding u are purely radiative, since the dissipation term − J ⋅ E covers the total current, while the E × H definition has contributions from ...
The magnetization field or M-field can be defined according to the following equation: =. Where is the elementary magnetic moment and is the volume element; in other words, the M-field is the distribution of magnetic moments in the region or manifold concerned.