The radius of the circular path of a charged particle in a magnetic field is given by

Explanation

Equating the magnetic force qvB to the required centripetal force mv squared over r and rearranging gives r equal to mv over qB. A heavier or faster particle therefore curves less, while a stronger field curves it more tightly. Because the radius depends on mass for a given charge and speed, this expression is the basis of the mass spectrometer.