An electric dipole of moment P is placed along the direction of electric field E. The work done in deflecting the dipole through \( 180^\circ \) is equal to
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → +2PE
The work done by an external agent in turning a dipole slowly equals the increase in its potential energy, where
\( \displaystyle U(\theta) = -P E \cos\theta \)
At first the dipole is along the field (\( \theta = 0^\circ \), stable equilibrium); after the deflection \( \theta = 180^\circ \).
\( U_i = -P E\cos 0^\circ = -P E \)
\( U_f = -P E\cos 180^\circ = +P E \)
\( \displaystyle W = U_f - U_i = P E - (-P E) = +2 P E \)