Nov 16, 2022
In the vacuum, inside a fixed ring of radius R with fixed charge Q uniformly distributed, there is a point charge with charge q and mass m moving in the plane of the ring due tue the electrostatic force. It moves in the small region around the center of the ring, and the motion is periodic along a closed curve. The area of the region enclosed by the curve is S. Denote the distance from the center to the point charge as r, and r≪R. Find the magnetic induction B at the center of the ring.