Paragraph: As a charged particle q moving with a velocity v enters a uniform magnetic field B , it experiences a force f = q ( v B ) . For =0^ or 180^ , being the angle between v and B , force experienced is zero and the particle passes undeflected. For =90^ , the particle moves along a circular arc and the magnetic force (qvB) provides the necessary centripetal force ( mv ^2 r ) . For other values of ( 0^ . , 180^ ,