An electric dipole is placed in a non-uniform electric field, such that the dipole moment is parallel to the electric field. The dipole will experience
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → a force only
The torque on a dipole is \( \vec{\tau} = \vec{p}\times\vec{E} \), which is zero when \( \vec{p} \) is parallel to \( \vec{E} \). The net force is zero only in a uniform field; in a non-uniform field the forces \( +q\vec{E} \) and \( -q\vec{E} \) on the two charges are unequal, so a net force acts (towards the region of stronger field when \( \vec{p} \parallel \vec{E} \)).
Option (1) a torque only. — Incorrect. The torque is zero because \( \vec{p} \) is parallel to \( \vec{E} \).
Option (2) both torque and force. — Incorrect. There is a force, but no torque.
Option (3) neither force nor torque — Incorrect. This holds only in a uniform field; here the field is non-uniform.
Option (4) a force only — Correct. No torque (\( \vec{p} \parallel \vec{E} \)) but a net force (non-uniform field).
NCERT (2026-27):
Dipole in a Uniform External Field – “… The general case is involved, so let us consider the simpler situations when p is parallel to E or antiparallel to E. In either case, the net torque is zero, but there is a net force on the dipole if E is not uniform.”