Lorentz force law

Lorentz’s force law describes how the electric field and magnetic field affect a moving charge

where is the magnetic field strength. Along with Maxwell’s equations, it is one of the fundamental rules describing Electrodynamics. It is also the principle that enables the Velocity selector for charged particles.

Remarks

Notice that by nature of the forces perpendicularity, any moving charged particle experiences centripetal acceleration in a magnetic field and thus if the particle is otherwise free it undergoes circular motion. If there is a component of the particle’s velocity that is parallel to the magnetic field, the overall effect is a helical path. The magnetic force does no work, rather it changes the direction of a charged particle’s existing kinetic energy.