Question

Two charges $+q$ and $-q$ are placed at a distance $a$ in a uniform electric field. The dipole moment of the combination is $2 q a(\cos \theta \hat{ i }+\sin \theta \hat{j})$, where, $\theta$ is the angle between the direction of the field and the line joining the two charges. Which of the following statement(s) is/are correct?

• A. The torque exerted by the field on the dipole vanishes
• B. The net force on the dipole vanishes
• C. The torque is independent of the choice of coordinates
• D. The net force is independent of ‘a’.

Answer 1

Answer: (B), (C), (D)

The situation can be diagrammatically as,

The dipole moment,
$P =2 q a(\cos \theta \hat{ i }+\sin \theta \hat{ j })$
The net force on the dipole is always zero while net torque on the dipole is not zero.