A square conducting loop of side 2a lies in the z=0 plane and carries a current in the counterclockwise direction. Show that at the center of the loop H = sqrrt2*I/pi*a in the z direction. I am stuck in this problem. Heres what Ive got. I placed the center of the loop at the origin. Im using Biot-Savarts Law. I found an R vector to be sqrt x^2 + y2 in the rho direction and cos x/sqrt x^2 + y2 in the phi direction. Heres where Im stuck. When I go to do the integral, my dl depends on the side im integrating. So if im my dl is dx, i dont know how to cross that why R because R has the unit vectors rho and phi.