The Lorentz force is the summation of both the Electric Force and the Magnetic Force that act on an object.

Definition

Formula

Lorentz Force

Terms

For the magnetic force to contribute,

Implications

In the case where the external magnetic and electric fields can be controlled, and are equal in magnitude, i.e.

Then the only way for the particle to not experience any force (and therefore change direction) is if:

This allows us to filter particles of certain velocities. Such a principle was used in by J.J Thompson in his experiment.