Question

An electric dipole of dipole moment `vecp` is kept in a uniform electric field `vecE`. The amount of work done to rotate it from the position of stable equilibrium to that of unstable equilibrium will be ______.

Options

• 2pE

• −2pE

• pE

• zero

Answer 1

An electric dipole of dipole moment `vecp` is kept in a uniform electric field `vecE`. The amount of work done to rotate it from the position of stable equilibrium to that of unstable equilibrium will be 2pE.

Explanation:

The amount of work done to rotate an electric dipole from an angle θ₁ to θ₂ is given by

W = pE(cos θ₁ − cos θ₂)

The dipole is rotated from the position of stable equilibrium, i.e. θ₁ = 0°, to that of unstable equilibrium, i.e. θ₂ = 180°

∴ Work done (W) = pE(cos 0° − cos 180°)

W = pE[(1 −(−1)]

= pE (2)

⇒ 2 pE