Posted by P on .
A flat thin nonconducting ring has an inner radius and an outer radius . The disk is uniformly charged with charge per unit area .
(a) What is the electric field at the center, , of the ring? Express your answer in terms of the following variables, if necessary, , , and the constant (if needed, enter pi for , epsilon_0 for , sigma for , R_1 for .. etc).
unanswered
(b)What is the magnitude of the electric field at point which is a distance x above the point ? The line is perpendicular to the plane of the ring. Express your answer in terms of the following variables, if necessary, , , , and the constant (if needed, enter pi for , epsilon_0 for , sigma for , R_1 for .. etc).

Physivs 
Anonymous,
for part (a) ans is 0.