A dipole placed in uniform electric field experiences:

Solution

An electric dipole consists of two point charges, +q and –q, separated by a small fixed distance 2a, with dipole moment p = q × 2a directed from –q to +q. When this dipole is placed in a uniform electric field E, each charge experiences an electric force: ●      The positive charge experiences a force F = +qE in the direction of the field. ●      The negative charge experiences a force F = –qE in the opposite direction. Since the electric field is uniform, the magnitudes of the forces on +q and –q are equal and opposite, and they act along parallel lines. Therefore: ●      Net force on the dipole = 0
  ⇒ No translational motion (i.e., no linear acceleration). However, the two equal and opposite forces are separated by a distance, and hence form a couple, resulting in a torque τ on the dipole. The torque experienced by the dipole is given by:
  τ = p × E
  Or in scalar form:
  τ = pE sinθ,
  where θ is the angle between the dipole moment p and the electric field E. This torque tends to align the dipole along the direction of the electric field.