Question

chapter 5 - problem 30. a negative charge is placed at the center of a ring of uniform positive charge. what is the motion (if any) of the charge? what if the charge were placed at a point on the axis of the ring other than the center?

Answer 1

There is no motion of the charge except along the axis of the ring.

(All charges on the ring are equivalent, with no net force perpendicular to the axis of the ring)

The electric potential of the axis of the ring decreases as the charge is moved away from the center of the ring,

The force on the negative charge will always be directed towards the center of the ring. (It would take work to move the charge "away" from the ring)