When a beam of charged particles, such as electrons or protons, travels through a magnetic field, each particle experiences a magnetic force if its motion is not parallel to the field.
For motion at right angles to the magnetic field, the force acts at right angles to both the particle's velocity and the magnetic field. The direction of the force depends on the sign of the charge: a positive particle and a negative particle moving in the same direction through the same field are deflected in opposite directions.
This magnetic force does not change the speed of the particle. Instead, it continuously changes the direction of motion, causing the particle to follow a circular or helical path. The radius of the path depends on the particle's mass, speed, charge, and the strength of the magnetic field.
Using the simulation below, change the charge of the particle or the strength of the magnetic field and observe how the deflection of the charged particle changes.