2023 Electric Charges and FieldsElectric Dipole in a Uniform Electric Field Medium Question 5 of 42 in Electric Charges and Fields

An electric dipole is placed at an angle of $30^\circ$ with an electric field of intensity $2\times10^5\ NC^{-1}$. It experiences a torque equal to $4\ Nm$. Calculate the magnitude of charge on the dipole, if the dipole length is 2 cm.

A 2 mC
B 8 mC
C 6 mC
D 4 mC

The answer is A.

Solution

Using $\tau=pE\sin\theta$ with $p=q\times2a$ gives $q=2\ mC$.

$\vec{\tau}=\vec{p}\times\vec{E}$ $|\vec{\tau}|=pE\sin\theta\Rightarrow4=q\times2a\times E\sin30^\circ$ $q=\frac{4}{(2\times10^{-2})\times2\times10^5\times\left(\frac{1}{2}\right)}$ $=2\times10^{-3}\ C=2\ mC$

Concept torque on a dipole

Electric Charges and Fields in past papers

42 questions from this chapter have appeared across 23 exam years.