A slightly divergent beam of charged particles accelerated by a Potential difference V propogates from a point A along the axis of a solenoid. The beam is brought into focus at a distance l from the point A at two successive values of magnetic induction `B_1 and B_2.` Find the specific charge `q//m` of the particles.

Answer

`[(8 pi^(2)V)/(l^(2) (B_(2) - B_(1))^(2))]`