When a charged particle moves on uniform magnetic field (B), it experience a force F as F= Bqv sinΘ, where q is charge particle, v be its velocity and Θ be is angle between B and v. This force is acting toward the motion of the circle or motion is circular. The direction of force F and distance covered s are always perpendicular to each other such that, work done W = FS cos90 = 0. so, the magnetic force does no work done but moves the particle in circular motion.