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
Magnetic flux boundary ∂Σ and, secondly, as the change of magnetic flux through the open surface Σ. This equation is the principle behind an electrical generator. By way of contrast, Gauss's law for electric fields, another of Maxwell's equations, is where Note that the flux of E through a closed surface is "not" always zero; this indicates the presence of "electric monopoles", that is, free positive or negative charges. Magnetic flux In physics, specifically electromagnetism, the magnetic flux (often denoted or ) through a surface is the surface integral of the normal component of the magnetic field B passing through that surface.