Question

An electric dipole is placed at an angle of ${30}^o$ with an electric field of intensity $2\times {10}^{5}N{C}^{-1}$. It experiences a torque equal to $4N$ $m$. The charge on the dipole of the dipole length is $2cm$ is

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

Answer 1

The correct option is C $2mC$

Here $E=2\times {10}^{5}N{C}^{-1},l=2cm,\tau =4Nm$
Torque $\overrightarrow{\tau }=\overrightarrow{p}\times \overrightarrow{E}=pE\sin \theta$
$\therefore 4=p\times 2\times {10}^5\times \sin {30}^o$
or $p=4\times {10}^{-5}Cm$
$\therefore$ Charge $q=\frac{p}{l}=\frac{4\times {10}^{-5}Cm}{0.02m}=2\times {10}^{-3}C=2mC$