A dipole of dipole moment $\vec{p}$ is kept along an electric field $\vec{E}$ such that $\vec{p}$ and $\vec{E}$ are in the same direction. Find the work done in rotating the dipole by an angle $\pi$.
Answer & explanation
Correct answer: option 1
$ W = \Delta U = U_2 - U_1 $
$U_2 = - E p cos\pi = Ep$
$ U_1 = -E p cos 0^o = - Ep$
$ W = 2Ep$