Question

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

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

Answer 1

Answer: (E)

Torque on dipole is $\tau =pE\sin \theta$
$\tau =q\times 2lE\sin \theta$
$\Rightarrow$ $q=\frac{\tau }{2El\sin \theta }$
Given, $\tau =4Nm,E=2\times {10}^{5}N{C}^{-1},$
$l=2\times {10}^{-2}m,\theta =30{}^{\circ }.$
$\therefore$ $q=\frac{4}{2\times 2\times {10}^5\times 2\times {10}^{-2}\times \sin 30{}^{\circ }}$
$\Rightarrow$ $q=2mC$