Q. An electric dipole consists of two opposite charges each 0.05$\mu C$ separated by 30 mm. The dipole is placed in an uniform external electric field of $10^{6}NC^{- 1}.$ The maximum torque exerted by the field on the dipole is
A) $6 \times 10^{- 3}N - m$
B) $3 \times 10^{- 3}N - m$
C) $15 \times 10^{- 3}N - m$
D) $1.5 \times 10^{- 3}N - m$
Explanation
(d) Given, $q = 0.05\mu C = 5 \times 10^{- 8}C$
$2a = 30mm = 0.03m$
$E = 10^{6}NC^{- 1}$
Torque acting on an electric dipole placed in an uniform electric field
$\tau = pE\sin\theta$
For maximum torque $\theta = 90{^\circ}$
$\therefore\ \ \ \tau_{\max\ } = pE = E(q \times 2a)$
$= 10^{6} \times 5 \times 10^{- 8} \times 0.03$
$= 1.5 \times 10^{- 3}N - m$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.