Question

An electric dipole is placed at an angle of 30° with an electric field of intensity 2 x 10⁵ NC^-1. It experiences a torque equal to 4 N m. Calculate the magnitude of charge on the dipole, if the dipole length is 2 cm.

(1) 6 mC

(2) 4 mC

(3) 2 mC

(4) 8 mC

Answer 1

Correct option is (3) 2 mC

\(\tau\) on dipole = \(\vec p\ \times\ \vec E\)

\(\tau\) = pEsin θ

4 = q x \(\ell\) x E x sin 30°

4 = q x 2 x 10^-2 x 10⁵ x \(\frac{1}{2}\)

q = 2 x 10^-3

q = 2 mC