An electric dipole is kept in an electric field which is increasing in +x direction. The dipole moment of the dipole is also along the +x direction. Which of the following options is correct for the electric dipole.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Electric dipole will experience a net force in +x direction.
In a non-uniform field the two charges of a dipole feel forces of different sizes, so there is a net force. The positive charge is at the larger \( x \), where the field is stronger.
\( \displaystyle F = q E(x + 2a) - q E(x) \approx p\,\frac{dE}{dx} \)
With \( \vec{p} \) along \( +x \) and \( dE/dx \gt 0 \), the force is along \( +x \). As \( \vec{p} \) is parallel to \( \vec{E} \), the torque \( \vec{p}\times\vec{E} \) is zero.
Option (1) Electric dipole will not experience any force in the presence of the electric field \( (\vec{E}) \). — Incorrect. The field is not uniform, so the two forces do not cancel.
Option (2) Electric dipole will experience force and try to align perpendicular to the direction of electric field \( (\vec{E}) \). — Incorrect. The dipole is already aligned with the field, so there is no torque to turn it.
Option (3) Electric dipole will experience a net force in +x direction. — Correct. The net force \( p\,dE/dx \) points towards the stronger field, along \( +x \).
Option (4) Electric dipole will experience a net force in -x direction. — Incorrect. A dipole parallel to the field is pulled towards the stronger field, not away from it.
NCERT (2026-27):
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.”
Dipole in a Uniform External Field – “… It is easily seen that when p is parallel to E, the dipole has a net force in the direction of increasing field.”