Question

For a filter to efficiently screen out particles depend on four factors, name those factors.

Answer 1

Write the equation of balance between the centripetal force acting on some particle and the magnetic force causeing that particle to go round:

$$mv^2/R=qvB,\\ mv/R=qB.$$

The 4 factors such as mass, velocity, charge and magnetic field are reasons which cause the particle to go in circles. The radius is a just a consequence.