question_answer

An electric dipole of moment \[\overrightarrow{p}\] is placed normal to the lines of force of electric intensity \[\overrightarrow{E}\], then the work done in deflecting it through an angle of \[180{}^\circ \] is              [BVP 2003]

A)                    \[pE\]

B)                                      \[+\,2pE\]

C)                    \[-2pE\]

D)                                      Zero

Correct Answer: D

Solution :

                    Work done \[=\int_{\,90}^{\,270}{pE\sin \theta \,d\theta }=[\,-\,pE\cos \theta ]_{\,90}^{\,270}=0\]