Question

A light rod is hinged (free to rotate) at its centre $O$ as shown in figure. Two point charges of same magnitude $+q$ are kept at its two ends. The rod is placed in uniform electric field $E$ as shown. Space is gravity free. The direction of force exerted by the hinge on the rod is

• A. rightwards
• B. leftwards
• C. upwards
• D. downwards

Answer 1

The correct option is B leftwards

FBD of two charges in uniform electric field is shown in figure.


From FBD, net forces $F_{net}$ on the two charges,

$F_{\text{net}}=2qE$ (towards right)

From the figure we can deduce that, charges are in rotational equilibrium.

To maintain it in translational equilibrium, the hinge will apply equal and opposite force $F=2qE$ towards left.

Hence, option (b) is the correct answer.