# Fig. 3.2 — Electric dipole in an electrostatic field

(a) An electric dipole pd , formed by two charges ±q of equal magnitude and opposite sign with separation l , in a uniform external electromagnetic field Ei experiences a torque that tends to align it with the field direction. (b) The stable equilibrium, i.e., the minimum of the the potential energy, is reached when pd is parallel to Ei and (c) the unstable equilibrium, i.e., the maximum of the potential energy, when pd is antiparallel to Ei.

Fig. 3.2 — Electric dipole in an electrostatic field