Key Idea: Flemings left hand rule will explain about the path of charged particle. According to question, the magnetic field is perpendicular to the direction of motion of charged particle. Force on the charged particle is given by F=qvB where q = magnitude of charged particle v = velocity of charged particle B = magnetic field According to Flemings left hand rule, the force is perpendicular to the velocity of the particle. This force in magnitude remain same but the direction of charged particle goes on changing and always perpendicular to the velocity of the particle, so the particle will move in a circular orbit. The magnetic force does not goes any change in its kinetic energy which implies that speed is constant or unchanged.