An electric dipole of dipole moment $\vec p$ is rotated in an electric field of magnitude E from the most stable orientation to most unstable orientation. The work done in the process is:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 2pE
The potential energy (U) of a dipole is -
$U=-\vec p.\vec E=-pE\cos θ$
∴ Work done in rotating the dipole (W) is -
$W=U_{final}-U_{initial}$
$=pE(\cos 180°)-(-pE\cos 0°)$
$=pE+pE$
$=2pE$