A particle specified charge (q/m) is projected from the origin of coordinates with initial velocity [u^i−v^j]. Uniform electric magnetic fields exists in the region along the +y direction, of magnitude E and B. The particle will definitely return to the origin once if.
Thelical motion of the particle-
2mvqE=(2πmqB)n
n=BvπE
So, BvπE should be an integer.