1. The problem statement, all variables and given/known data The electric field, E a distance z above a circular loop of charge density lambda, radius r, in the x-y plane centred on the origin, is given by E(z)=[lambda z r] i(subscript z)/[2 epsilon0((z^2 + r^2)^(3/2))] a) using this, find the electric field, E, a distance z above a disc of radius R and surface charge density sigma (8 marks) b) describe the limits of E for the disc at R tends to infinity and z>>0 (4 marks) 3. The attempt at a solution a) E(z)=[sigma z R] i(subscript z)/[2 epsilon0((z^2 + R^2)^(3/2))] I don't think that's going to gain me the full 8 marks and I have no idea what to do next. Please help b) I can't even make sense of it. How can z>>R if R tends to infinity?