Dipole

This article is about a general description of dipoles in physics and related fields. For detailed description of electric dipoles, see electric dipole moment. For detailed description of magnetic dipoles, see magnetic dipole. For other uses, see Dipole (disambiguation).

Field lines of a point dipole of any type, electric, magnetic, acoustic, etc.

In physics, a dipole (from Ancient Greek δίς (dís) 'twice' and πόλος (pólos) 'axis') is an electromagnetic phenomenon which occurs in two ways:

• An electric dipole formed by the separation of the positive and negative electric charges (typically in atomic and molecular systems).
• A magnetic dipole represents a sufficiently small magnet such as those due to atoms, molecules, and electrons.

The strength of a dipole, whether electric or magnetic, is characterized by its dipole moment, a vector quantity. Electric dipoles produce an electric field and experience forces and torques in an electric field that are proportional to their electric dipole moment. The same is true of magnetic dipoles with magnetic fields. Further, the equations for the magnetic dipole are nearly identical to their electric counterparts.

Electric dipoles are typically represented by a pair of equal but opposite electric charges separated by a small distance. The electric dipole moment points from the negative charge towards the positive charge and has a magnitude equal to the strength of each charge times the separation between the charges. Magnetic dipoles are typically modeled as a loop of constant current. The magnetic dipole moment points through the loop (according to the right hand grip rule), with a magnitude equal to the current in the loop times the area of the loop.