Magnetic charge is a property held by magnetic monopoles, pointlike topological defects that create radial magnetic fields. It measures how strongly they create and interact with magnetic fields. North poles have positive magnetic charges, and south poles have negative magnetic charges. It has dimensions of [current][length]. The relationship between the magnetic charge qm of a stationary point monopole at a position a and the value of its magnetic field strength B at a position r, with no further electric or magnetic fields, is given by Coulomb's law for magnetism with magnetic monopoles,