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.

Answer

B

Explanation

Time for the dipole to align along the direction of electric field will be
`t=T/4=(2pi)/(4)sqrt((ML)/(2qE))=pi/2sqrt((ML)/(2qE))`