ELECTRIC DIPOLE AND ITS PROPERTIES

Two equal and opposite charges (+q and -q) separated by a small distance constitute an electric dipole. Dipoles are physically important because in many molecules, such as water, the centres of positive and negative charge do not coincide even though the molecule as a whole is neutral, making the molecule behave like a tiny permanent electric dipole; other molecules acquire an induced dipole moment only when placed in an external electric field (developed further in section 1.7.4 on dielectrics). This section develops the dipole's own strength and direction (its dipole moment), the electric field the dipole itself produces at points on its axial line and its equatorial (perpendicular bisector) plane, and …