Question

A point particle of mass M is attached to one end of massless rigid non-conducting rod of length L. Another point particle of the same mass is attached to other end of the rod. The two particles carry charges +q and -q respectively. This arrangement is held in a region of a uniform electric field E, such that the rod makes a small angle q (say of about 5 degree) with the field direction. Find an expression for the maximum time needed for the rod to become parallel to the field after it is set free-

• A. T = 2p$\sqrt{\frac{ML}{2qE}}$
• B. T = $\frac { \pi } { 2 }$ $\sqrt{\frac{ML}{2qE}}$
• C. T = $\frac { 3 \pi } { 2 }$ $\sqrt{\frac{ML}{2qE}}$
• D. T = p$\sqrt{\frac{2ML}{qE}}$

Answer 1

Answer: (B)

T = $\frac { \pi } { 2 }$ $\sqrt{\frac{ML}{2qE}}$

Answer 2

Time period T = 2p$\sqrt { \frac { \mathrm { I } } { \mathrm { pE } } }$, I =$\frac { 2 \mathrm { ML } ^ { 2 } } { 4 } = \frac { \mathrm { ML } ^ { 2 } } { 2 }$ time to

parallel the field t =

= $\frac { \pi } { 2 } \sqrt { \frac { \mathrm { ML } ^ { 2 } } { 2 \times \mathrm { qLE } } }$ =