Thanks to Jack and John for constructive criticism. I will
think about this again. Perhaps most of you will approve
my initiative to invite Paul Tipler to join the phys-L list.
I did this after Clarence Bennett sent me Paul's e-mail
address and suggested I ask him for a clarification. The
reply is shown below. (That is the most valuable outcome
of this thread, I think.) We will probably start seeing
Paul's contributions soon.
======================================
From: Tipler@aol.com
To: kowalskiL@mail.montclair.edu
I guess the problem is in thinking that a uniformly charged ball
acts like a point charge.
The electric field due to a spherically symmetric uniformly charged
ball at a distance r from the center is proportional to r. (Figure 19-25
on page 643 of my 3rd edition). The force exerted by the ball on a
point charge (the proton) is thus similar to the force exerted by a
spring. It increases with distance from the center so there is a
position of stable equilibrium if the two charges are in a uniform
external field.
This calculation is given in the 4th edition (1999) in Example 25-11
on page 773.
I will join your group--but until I do, you may post this solution or
give it to anyone interested.
Paul T