dipôle

A dipole is a system consisting of two equal and opposite sources that are separated by a finite distance. In physics and chemistry, the term most often refers to an electric dipole—two opposite charges separated by a distance—but it also describes a magnetic dipole, arising from a loop of current or from pairs of magnetic poles. The opposing sources create a directional field and characteristic interactions with external fields.

Electric dipole moment is a key quantity associated with an electric dipole. It is defined as the vector μ = q d, pointing from the negative to the positive charge, where q is the charge and d is the separation. In molecules, a permanent dipole moment indicates polarity and affects properties such as solubility, dielectric behavior, and response to electric fields. The magnitude is commonly expressed in Debye units (1 Debye ≈ 3.33564×10^-30 C·m).

Magnetic dipoles arise from circulating currents or from pairs of magnetic poles. The magnetic dipole moment m of a current loop equals I A, where I is the current and A is the loop area. Magnetic dipoles are found in bar magnets and in many electronic devices. They interact with magnetic fields and with each other through dipole-dipole coupling, with energy that depends on orientation and separation.

Dipole-dipole interactions fall off roughly as 1/r^3 and are highly orientation-dependent. They influence molecular alignment in solvents, phase behavior, spectroscopy, and hydrogen-bond networks, as well as the design of electronic and radio-frequency components. In engineering, the half-wave dipole is a classic antenna that radiates as an electric dipole.

The concept is used across languages; in French, dipôle or dipôle électrique denotes similar ideas, reflecting the broad applicability of the dipole abstraction in science.