Magnetic dipole magnetic dipole as the distance from the source increases. In classical physics, the magnetic field of a dipole is calculated as the limit of either a current loop or a pair of charges as the source shrinks to a point while keeping the magnetic moment constant. For the current loop, this limit is most easily derived for the vector potential. Outside of the source region, this potential is (in SI units) with 4"π r" being the surface of a sphere of radius "r"; and the magnetic flux density (strength of the B-field) in teslas is In spherical coordinates with the
Permeability (electromagnetism) example in a Newton–Raphson iterative solution scheme that computes the changing saturation of a magnetic circuit. Permeability is the inductance per unit length. In SI units, permeability is measured in henries per metre (H·m = J/(A·m) = N·A). The auxiliary magnetic field H has dimensions current per unit length and is measured in units of amperes per metre (A·m). The product "µ" H thus has dimensions inductance times current per unit area (H·A/m). But inductance is magnetic flux per unit current, so the product has dimensions magnetic flux per unit area, that is, magnetic flux density. This is the magnetic