Let us look at a charged particle which is moving in a circle with a constant speed. This is uniform circular motion that you have studied earlier. Thus, there must be a net force acting on the particle, directed towards the centre of the circle. As the speed is constant, the force also must be constant, always perpendicular to the velocity of the particle at any given instant of time. Such a force is provided by the uniform magnetic field \(\overrightarrow{B}\) perpendicular to the plane of the circle along which the charged particle moves.

Let us look at a charged particle which is moving in a circle with a c

1.	Let us look at a charged particle which is moving in a circle with a constant speed. This is uniform circular motion that you have studied earlier. Thus, there must be a net force acting on the particle, directed towards the centre of the circle. As the speed is constant, the force also must be constant, always perpendicular to the velocity of the particle at any given instant of time. Such a force is provided by the uniform magnetic field \(\overrightarrow{B}\) perpendicular to the plane of the circle along which the charged particle moves.
Answer» When a charged particle moves in uniform circular motion inside a uniform magnetic field \(\overrightarrow{B}\) in a plane perpendicular to \(\overrightarrow{B}\) the centripetal force is the magnetic force on the particle. As in any UCM, this magnetic force is constant in magnitude and perpendicular to the velocity of the particle.