An electric dipole of dipole moment \( 5 \times 10^{-6}\,\mathrm{C\,m} \) is placed in a uniform electric field of \( 10^{-2}\,\mathrm{N/C} \) making an angle of \( 30^\circ \) with the direction of the field. The torque exerted by the electric field on the dipole is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \( 2.5 \times 10^{-8}\,\mathrm{N\,m} \)
In a uniform field the forces on the two charges of a dipole are equal and opposite, so the net force is zero, but they form a couple. The torque on the dipole is
\( \displaystyle \tau = pE\sin\theta \)
\( p = 5\times10^{-6}\,\mathrm{C\,m} \)
\( E = 10^{-2}\,\mathrm{N\,C^{-1}} \)
\( \theta = 30^\circ,\ \sin 30^\circ = 0.5 \)
\( \displaystyle \tau = 5\times10^{-6} \times 10^{-2} \times 0.5 = 2.5\times10^{-8}\,\mathrm{N\,m} \)
Note: NTA picked this question from an NCERT (2026-27) exercise and changed the figures. Do not ignore NCERT while practising numericals.
NCERT (2026-27):
Exercises – …
