Magnetic constant: Difference between revisions

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== Footnotes ==
== Footnotes ==
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The magnetic constant μ0 (equal to the vacuum permeability, also known as the permeability of free space) is a universal physical constant, relating mechanical and electromagnetic units of measurement. In the International System of Units (SI), its value is exactly expressed by:

N/A2 = 4π×10−7 H/m, or approximately 1.2566×10−6 H/m.[1]

This value is a consequence of the definition of the ampere in terms of forces between wires.[2] In vacuum, the magnetic constant is the ratio of the magnetic B-field (for calculating Lorentz force) to the H-field (calculated from currents):

The magnetic constant μ0 is related to the electric constant ε0 and to the speed of light in vacuum by c ² ε0 μ0 = 1.

Terminology

Historically, the constant μ0 has had different names. A now rather obsolete term is "magnetic permittivity of vacuum". In the 1987 IUPAP Red book this constant was called permeability of vacuum.[3] Currently the nomenclature in physics is magnetic constant.[1][4] The vacuum permeability μ = μrμ0 is equal to μ0.

Footnotes