Vacuum permeability

Vacuum permeability, denoted μ₀, is the proportionality constant relating magnetic flux density to magnetic field strength in vacuum. It also appears in electromagnetic equations and the definition of electrical units.

Magnetic flux density: A vector field describing the strength and direction of magnetic effects, measured in teslas. In vacuum, μ₀ relates this field to magnetic field strength.
SI base units: The seven reference units from which the International System of Units derives other units. The modern status of μ₀ follows from how SI defines its base units.
Vacuum permittivity: The electric constant ε₀ relating electric displacement to electric field in vacuum. Together with μ₀, it determines the speed of electromagnetic waves in vacuum.
Biot–Savart law: A law calculating the magnetic field produced by a steady electric current. Its vacuum expression includes μ₀ as the factor scaling current-generated fields.
Ferromagnetism: A form of magnetism in which aligned magnetic moments produce strong, persistent magnetization. Ferromagnetic materials can have permeability far greater and less constant than μ₀.
Magnetic field strength: A vector quantity describing the magnetizing field produced by currents and magnetic materials, measured in amperes per meter. It is the field quantity multiplied by μ₀ to obtain magnetic flux density in vacuum.
2019 redefinition of the SI: A revision of the International System of Units that fixed values of seven defining constants. It made μ₀ experimentally determined rather than exactly fixed.
Magnetic constant: An alternative name for vacuum permeability, especially in standards and engineering contexts. This synonym is used where μ₀ is treated as a defined physical constant.
Inductance: A circuit property that quantifies magnetic flux linkage produced per unit current. Magnetic field calculations involving coils often depend on μ₀.
Diamagnetism: A weak magnetic response in which an applied field induces magnetization opposing that field. Its material response differs from the fixed vacuum reference μ₀.

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