An electric dipole is placed in an external uniform electric field. The net electric force on the dipole
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → is always zero
A dipole is a pair of equal and opposite charges, +q and −q. In a uniform field both charges feel forces of the same magnitude qE in opposite directions.
\( \displaystyle \vec{F}_{\mathrm{net}} = q\vec{E} + (-q)\vec{E} = 0 \)
This holds for every orientation and every value of the dipole moment. What the field does exert is a torque, \( \vec{\tau} = \vec{p} \times \vec{E} \), which turns the dipole towards the field direction.
Why the other options are incorrect
Option (2) depends on the orientation of the dipole — Incorrect. The orientation changes the torque (\( \tau = pE\sin\theta \)), not the net force.
Option (3) can never be zero — Incorrect. The net force is zero in every uniform field; it is non-zero only in a non-uniform field.
Option (4) depends on the dipole moment of the dipole — Incorrect. The dipole moment again affects the torque; the two forces cancel whatever the value of p.
NCERT (2026-27):
Dipole in a Uniform External Field – “… There is a force qE on q and a force –qE on –q. The net force on the dipole is zero, since E is uniform. However, the charges are separated, so the forces act at different points, resulting in a torque on the dipole.”
Dipole in a Uniform External Field – “… What happens if the field is not uniform? In that case, the net force will evidently be non-zero.”