1. The problem statement, all variables and given/known data A thin rubber ring of radius R lies in the xy-plane and is centered at the origin. The ring carries line charge density λ=λo*sin(Ø), with a constant λo with units C/m. define tan(Ø)=y/x. Calculate the magnitude and direction of the electric field E(z) created by the ring on points on the positive z axis. 2. Relevant equations E=kq/r^2 3. The attempt at a solution Symmetry implies only the component Ez will be nonzero along the z axis. Desiring to integrate over Ø, my limits of integration will be 0 to pi. Now dE=k*dq/r^2 with r=(R^2+z^2). Q/R=λo*sin(Ø) so dQ=R*λo*cos(Ø) dØ and dEz= k*R*λo*cos(Ø) dØ/(R^2+z^2) however, integrating this over Ø results in multiplying everything by sin(pi)-sin(0) = 0, so clearly I've made at least one mistake here. All help is appreciated!