Chapter 22, Problem 76GP

Predict/Calculate A beam of protons with various speeds is directed in the positive x direction. The beam enters a region with a uniform magnetic field of magnitude 0.52 T pointing in the negative z direction, as indicated in Figure 22-58. It is desired to use a uniform electric field (in addition to the magnetic field) to select from this beam only those protons with a speed of 1.42 × 10⁵—that is, only these protons should be undeflected by the two fields. (a) Determine the magnitude and direction of the electric field that yields the desired result. (b) Suppose the electric field is to be produced by a parallel-plate capacitor with a plate separation of 2.5 cm. What potential difference is required between the plates? (c) Which plate in Figure 22-58 (top or bottom) should be positively charged? Explain.

Figure 22-58 Problem 76