Talk:Permeability constant
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The permeability constant or magnetic constant (μ0) is the permeability of vacuum (or of free space). It is a physical constant not defined by other physical constants.
It is defined as the ratio of magnetic field density to magnetic field strength in vacuum:
In SI units, the value is exactly expressed by:
μ0 = 4π×10−7 N/A2 = 4π×10−7 H/m