In Figure 23.83 a single circular loop of wire with radius R carries a large clockwise constant current , which
constrains a proton of mass M and charge e to travel in a small circle of radius r at constant speed around the center of the
loop, in the plane of the loop. The orbit radius r is much smaller than the loop radius R: .
(a) Draw a diagram of the proton orbit, indicating the direction that the proton travels, clockwise or counterclockwise.
Explain briefly.
(b)
What is the speed v of the proton, in terms of the known quantities , R, r, M, and e? Explain your work,
including any approximations you must make.
(c) The current was constant for a while, but at a certain time it began to decrease slowly, so that after the
current was . On your diagram of the proton orbit, draw electric field vectors at four
locations (one in each quadrant) and explain briefly.
(d) When the current decreases, does the proton speed up or slow down?