Question

Two points masses, \( m \) each carrying charges \( -q \) and \( +q \) are attached to the ends of a massless rigid non-conducting wire of length \( L \). When this arrangement is placed in a uniform electric field, then it deflects through an angle \( \theta \). The minimum time needed by rod to align itself along the field is

• A. \( \frac{2\pi mL}{qE} \)
• B. \( \frac{\pi mL}{2qE} \)
• C. \( \frac{\pi mL}{qE} \)
• D. \( \frac{2\pi qE}{mL} \)

Hint:

When dealing with torque in rotational motion, the time for alignment can be calculated using the equation involving the moment of inertia and torque.

Answer 1

The Correct Option is C

The time for the rod to align itself with the electric field depends on the torque applied due to the electric field. Using the relation \( \tau = I \alpha \) and the moment of inertia for a rod, the time is given by \( \frac{\pi mL}{qE} \).