. Velocity selector. Consider a charged particle moving through a region in which the electric field is perpendicular to the magnetic field, with both fields perpendicular to the initial velocity of the particle (Fig. P20.62). Such a device is called a velocity selector because for one particular value of the particle speed v_select the particle will travel straight through the device without being deflected, whereas particles with speeds that are either less than or greater than v_select will be deflected. Consider a case with E = 500 V/m and B = 0.25 T.
(a) When protons are used, what speed is selected?
(b) What is the speed selected for Ca²⁺ ions?
(c) If you were to use your selector with F^- ions, what change would be necessary?

Perspective view v < Vselect FE v = Vselect v> Vselect