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
Flux quantum state ψ(r, t) have a probability density defined as So the probability of finding a particle in a differential volume element dr is Then the number of particles passing perpendicularly through unit area of a cross-section per unit time is the probability flux; This is sometimes referred to as the probability current or current density, or probability flux density. As a mathematical concept, flux is represented by the surface integral of a vector field, where F is a vector field, and d"A" is the vector area of the surface "A", directed as the surface normal.For the second,n is the