Question

In which orientation a dipole placed in a uniform electric fields is in (i) stable (ii) unstable equilibrium

Answer 1

(i) In stable equilibrium the dipole moment is parallel to the direction of electric field (i.e., $\theta =0)$.
(ii) In unstable equilibrium $PE$ is maximum, so $\theta =\pi$, i.e., dipole moment is antiparallel to electric field.