(i) The dipole moment |P| = q × 2a
Force on -q at A = -qE
Force on +q at B = +qE
Net force on the dipole = qE – qE = 0
(ii) We know that work done in rotating an electric dipole from θ1 to θ2, (where θ 1 is the angle of the dipole with electric field) is given by,
W = pE (cos θ1 − cos θ2) now given θ1 = 0º, θ2 = 180º
∴ W = pE(cos 0 − cos 180) = 2pE