scalar constant μ0 linking the electromagnetic quantities and the mechanical quantities, obtained from the relation
where F/l is the magnitude of the lineic force between two straight parallel conductors of infinite length and negligible circular cross-section, placed at a distance d apart in vacuum and carrying electric currents I1 and I2
NOTE 1 – In vacuum, the product of the magnetic constant and the magnetic field strength H is equal to the magnetic flux density B:
B = μ0H
NOTE 2 – The magnetic constant is related to the electric constant ε0 and to the speed of light in vacuum c0 by the relation
μ0ε0c02 = 1
NOTE 3 – The value of the magnetic constant is exactly equal to
4π × 10−7 m kg s−2 A−2 = 1,256 637 061 4... μH/m
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