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A Greek mu with a nought subscript, the magnetic constant.
Also known as: Magnetic constant, Mu nought, Vacuum permeability, Mu zero
μ₀ measures how readily a vacuum supports a magnetic field. For most of the twentieth century it was exactly 4π×10⁻⁷ by the definition of the ampere; the 2019 redefinition made that value approximate, which is a rare case of a constant losing its exactness.
Denotes the magnetic constant, the permeability of vacuum, appearing in Ampère's law and the Biot–Savart law.
Contexts: Laboratory
Was exactly 4π×10⁻⁷ H/m under the pre-2019 definition of the ampere and is now a measured quantity, though the numerical change is far below any practical measurement.
Contexts: Laboratory
A Greek lowercase mu, a rounded form with a descending tail on the left, with a small numeral zero set below and to the right.