(i) Obtaining of the expression for torque experienced by an electric dipole
(ii) Effect of non-uniform electric field
(i)
Force on $+\mathit{q},\overrightarrow{\mathit{F}}=\mathit{q}\overrightarrow{\mathit{E}}$
Force on $-\mathit{q},\overrightarrow{\mathit{F}}=-\mathit{q}\overrightarrow{\mathit{E}}$
Magnitude of torque
$\mathit{\tau }=\mathit{q}\mathit{E}\times 2\mathit{a}\mathit{s}\mathit{i}\mathit{n}\mathit{\theta }$
$=2\mathit{q}\mathit{a}\mathit{E}\mathit{s}\mathit{i}\mathit{n}\mathit{\theta }$
$\overrightarrow{\mathit{\tau }}=\overrightarrow{\mathit{p}}\times \overrightarrow{\mathit{E}}$
(ii) If the electric field is non uniform, the dipole experiences a translatory force as well as a torque.