In physics, a multipole is any spatial arrangement of ( electrical or other) discrete charges or, in the magnetic case, of dipoles . By multipole expansion , a potential field can be approximated by point charges .
Important special cases are:
In physics, one considers the spherical multipole expansion of fields according to spherical surface functions and the associated multipole moments more generally . Then = 0 corresponds to the monopole, = 1 to the dipole, = 2 to the quadrupole, = 3 to the octupole, etc.