Charged Particle Paths in Magnetic Fields

A charged particle in a magnetic field follows a path that depends on the direction of its velocity. When the field is uniform and the particle moves perpendicular to it, the magnetic field is the main factor that controls the motion, especially in a vacuum. The magnetic force is always perpendicular to the direction of moti...

Consider a point mass m of charge Q moving perpendicular to a uniform magnetic field B.

The Lorentz force's magnitude is constant and is always perpendicular to its velocity. So, it cannot change the velocity's magnitude, only its direction. Hence, the particle's path is a circle with a radius r.