Chapter 22, Problem 13P

GO Figure 22-40 shows a proton (р) on the central axis through a disk with a uniform charge density due to excess electrons. The disk is seen from an edge-on view. Three of those electrons are shown: electron e_c at the disk center and electrons e_s at opposite sides of the disk, at radius R from the center. The proton is initially at distance z = R = 2.00 cm from the disk. At that location, what are the magnitudes of (a) the electric field $\stackrel{\to }{E_c}$ due to electron e_c and (b) the net electric field ${\stackrel{\to }{E}}_{s,\text{net}}$ due to electrons e_s? The proton is then moved to z = R/10.0. What then are the magnitudes of (с) $\stackrel{\to }{E_c}$ and (d) ${\stackrel{\to }{E}}_{s,\text{net}}$ at the proton's location? (e) From (a) and (c) we see that as the proton gets nearer to the disk, the magnitude of $\stackrel{\to }{E_c}$ increases, as expected. Why does the magnitude of ${\stackrel{\to }{E}}_{s,\text{net}}$ from the two side electrons decrease, as we see from (b) and (d)?

Figure 22-40 Problem 13.