Vacuum Permeability - Significance in Electromagnetism

Significance in Electromagnetism

The magnetic constant μ₀ appears in Maxwell's equations, which describe the properties of electric and magnetic fields and electromagnetic radiation, and relate them to their sources. In particular, it appears in relationship to quantities such as permeability and magnetization density, such as the relationship that defines the magnetic H-field in terms of the magnetic B-field. In real media, this relationship has the form:

where M is the magnetization density. In vacuum, M = 0.

In SI units, the speed of light in vacuum, c₀ is related to the magnetic constant and the electric constant (vacuum permittivity), ε₀, by the definition:

This relation can be derived using Maxwell's equations of classical electromagnetism in the medium of classical vacuum, but this relation is used by BIPM and NIST as a definition of ε₀ in terms of the defined numerical values for c₀ and μ₀, and is not presented as a derived result contingent upon the validity of Maxwell's equations.