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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 ...
μ 0 ≈ 12.566 × 10 −7 H/m is the magnetic constant, also known as the permeability of free space, ε 0 ≈ 8.854 × 10 −12 F/m is the electric constant, also known as the permittivity of free space, c is the speed of light in free space, [9] [10] The reciprocal of Z 0 is sometimes referred to as the admittance of free space and ...
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 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.
As before, it is defined by the equation ε 0 = 1/(μ 0 c 2), and is thus determined by the value of μ 0, the magnetic vacuum permeability which in turn is determined by the experimentally determined dimensionless fine-structure constant α: = = ,
The energy of a localized magnetic charge q m in a magnetic scalar potential is =, and of a magnetic charge density distribution ρ m in space =, where µ 0 is the vacuum permeability. This is analog to the energy Q = q V E {\displaystyle Q=qV_{E}} of an electric charge q in an electric potential V E {\displaystyle V_{E}} .
The CGS-to-SI correspondence of electromagnetic units as given was exact prior to the 2019 revision of the SI, until which the magnetic constant μ 0 was defined as 4π × 10 −7 N⋅A −2. As from the redefinition, μ 0 has an inexactly known value when expressed in SI units, with the exactness of the electromagnetic unit correspondence ...