In this demonstration particles are entering the region of the magnetic field with
their velocities being perpendicular to the magnetic field lines. In such a situation
the magnetic force serves to move the particles in a circular path. According to
the "right hand rule" the magnetic force acting on the particle always
remains perpendicular to its velocity.
The magnitude of the magnetic force is F = qvB_{⊥}, where q
is the magnitude of the charge of the particle, v its velocity, and B_{⊥}
is the magnitude of the perpendicular magnetic field.
This force can be also considered as the centripetal force F_{c} = mv^{2}/R,
where m is the particle's mass and R is the radius of the circular
tragectory.
Making two above expressions equal to each other and solving the resulting equation
for R we can easily find that the radius R of the circular path is
proportional to the velocity of the particle.
R = mv/qB_{⊥}
