Question

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

• A. $8\,mC$
• B. $4\,mC$
• C. $6\,mC$
• D. $2 \,mC$

Answer 1

Answer: (D)

$2 \,mC$

Answer 2

$\tau= pE \sin \theta$
$\tau= q \ell \operatorname{Esin} \theta$
$q =\frac{\tau}{\ell E \sin \theta}$
$q =\frac{4}{2 \times 10^{-2} \times 2 \times 10^{5} \times \frac{1}{2}}$
$q =2 \times 10^{-3} C$
$q =2 mC$