There are 7 charges, each with q = -5 nC distributed on a circle with radius R=3cm. The center of the circle is at the origin. The charges are at angles 0o, 45o, 90o, 135o, 180o, -90o, and -45o. (Note: A charge at -135o is missing.) a) What is the net electric field at the origin? b) Calculate the electric potential at the origin with respect to infinity.
The field in the center due to one point charge which has no opposite charge is
E=kq/r² = 9•10⁹•5•10⁻⁹/0.03²=5•10⁴ V/m
φ=7• kq/r = 7•9•10⁹•(-5•10⁻⁹)/0.03 =-1.05•10⁴ V