Two Concentric Cylinders The figure below shows two concentric cylindrical conductors separated by a thin insulating layer. The inner conductor has a radius a and carries a current I flowing out of the page. The outer conductor has an inner radius of a and an outer radius of b. It carries a current of I flowing into the page. The two currents are uniformly spread over their respective cross-sections. Find an expression for the magnitude of the magnetic field at a distance of r where a