Question

An electric dipole is placed at an angle of $30^{\circ}$ with an electric field of intensity $2 \times 10^{5} NC ^{-1}$. It experiences a torque equal to $4\, Nm$. Calculate the charge on the dipole if the dipole length is $2\, cm$.

• A. $8\, mC$
• B. $4\, mC$
• C. $8\, \mu C$
• D. $2\, mC$

Answer 1

Answer: (D)

Torque on dipole is $\tau= pE \sin \theta$
$\tau=q \times 2 E l \sin \theta$
$\Rightarrow q=\frac{\tau}{2 E l \sin \theta}$
$\Rightarrow q=\frac{4}{2 \times 2 \times 10^{5} \times 2 \times 10^{-2} \times \sin 30^{\circ}}$
or $q=2\, mC$