18. An electric dipole has the magnitude of its charge as q and its dipole moment is p. It is placed in uniform electric field E. If its dipole moment is along the direction of the field, the force on it and its potential energy are respectively ?

An electric dipole has the magnitude of its charge as q and its dipole moment is p. It is placed in uniform electric field E. If its dipole moment is along the direction of the field, the force on it and its potential energy are respectively ?

(a) q.E and max

(b) 2q.E and min

(c) q.E and p.E

(d) zero and min

Answer :  (d) zero and min

\( \text{At } 90^\circ, \, U = 0 \)

\( \text{which is the reference} \)

\( F_{\text{net}} = 0 \)

\( U = -pE \cos \theta \)

\( \quad = -pE \cos 0^\circ \)

\( \quad = -pE \)

\( \text{minimum value} \)