A point particle of mass M is attached to one end of a massless rigid non-conducting rod of length L. Another point particle of the same mass is attached to the 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 `theta` (say of about 5 degree) with the field direction, fig. Find an expression for the minimum time needed for the rod to become parrallel to the field after it is set free.

Options

A. `t=(pi)/(2)sqrt((mL)/(2qE))`
B. `t=(pi)/(2)sqrt((mL)/(qE))`
C. `t=(pi)/(2)sqrt((2mL)/(qE))`
D. `t=(pi)/(2)sqrt((3mL)/(qE))`

Answer

1

Explanation

`V_(1)=(Q)/(4piepsilon_(0)R)+(Q_(2))/(4piepsilon_(0)sqrt(2)R)`
and `V_(2)=(Q_(1))/(4piepsilon_(0)sqrt(2)R)+(Q_(2))/(4piepsilon_(0)R)`
`W_(1 rarr 2)=q(V_(2)-V_(1))`