You wish to design a velocity selector (see Problem 62 and Fig. P20.62) that will allow protons to pass through only if they have a speed of 500 m/s.
(a) If the magnetic field is B = 0.050 T, what electric field do you need?
(b) You decide to produce this electric field using a parallel-plate capacitor with a plate spacing of 1.0 mm. What is the electric potential across the plates?
(c) Will your velocity selector also work for Li⁺ ions? For Mg²⁺ ions? Explain why or why not.

Figure 20.62

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