question_answer

Torque acting on electric dipole of dipole moment \[\vec{p}\] placed in uniform electric field \[\vec{E}\] is:         [AIPMT 2001]

A) \[\vec{p}\times \vec{E}\]

B) \[\vec{p}\,.\,\vec{E}\]    

C) \[\vec{p}\times \vec{E}\times \vec{p}\]

D) \[\frac{\vec{E}\,.\,\vec{p}}{{{p}^{2}}}\]

Correct Answer: A

Solution :

[a] If electric dipole is placed perpendicular to electric field, in this case net force on dipole will be zero but torque on dipole will not be zero.

Torque  \[\tau =pE\sin \theta \]

or         \[\vec{\tau }=\vec{p}\times \vec{E}\]