Consider that the magnetic force on a moving charge is F = qvB sin θ, with the force’s direction
determined by the right-hand rule. In a constant magnetic field that is perpendicular to a particle’s
direction of motion, this leads to a circular path. (Do you see why?) You should also know from Physics
I that an object undergoing circular motion experiences an acceleration (pointed inward): a = v2/rc
where rc is the circle’s radius.