Editing Dipole (section)

== Classification ==
[[File:VFPt dipole electric.svg|thumb|250px|Electric field lines of two opposing charges separated by a finite distance.]]
[[File:VFPt dipole magnetic2.svg|250px|right|thumb|Magnetic field lines of a ring current of finite diameter.]]
[[File:VFPt dipole point.svg|thumb|250px|Field lines of a point dipole of any type, electric, magnetic, acoustic, etc.]]

A ''physical dipole'' consists of two equal and opposite point charges: in the literal sense, two poles. Its field at large distances (i.e., distances large in comparison to the separation of the poles) depends almost entirely on the dipole moment as defined above. A ''point (electric) dipole'' is the limit obtained by letting the separation tend to 0 while keeping the dipole moment fixed. The field of a point dipole has a particularly simple form, and the order-1 term in the [[multipole expansion]] is precisely the point dipole field.

Although there are no known [[magnetic monopole]]s in nature, there are magnetic dipoles in the form of the quantum-mechanical [[Spin (physics)|spin]] associated with particles such as [[electron]]s (although the accurate description of such effects falls outside of classical electromagnetism). A theoretical magnetic ''point dipole'' has a magnetic field of exactly the same form as the electric field of an electric point dipole. A very small current-carrying loop is approximately a magnetic point dipole; the magnetic dipole moment of such a loop is the product of the current flowing in the loop and the (vector) area of the loop.

Any configuration of charges or currents has a 'dipole moment', which describes the dipole whose field is the best approximation, at large distances, to that of the given configuration.  This is simply one term in the multipole expansion when the total charge ("monopole moment") is 0—as it ''always'' is for the magnetic case, since there are no magnetic monopoles.  The dipole term is the dominant one at large distances:  Its field falls off in proportion to {{sfrac|1|''r''<sup>3</sup>}}, as compared to {{sfrac|1|''r''<sup>4</sup>}} for the next ([[quadrupole]]) term and higher powers of {{sfrac|1|''r''}} for higher terms, or {{sfrac|1|''r''<sup>2</sup>}} for the monopole term.