Hi guys, I was wondering if someone could help explain something to me. I am just starting out learning about Ampere's law. I am looking at this example in the book and I don't get it. They have a cylindrical conductor with Radius R and current I. The current is uniformly distributed over the cross sectioanl area of the conductor. They take a surface that is like an extended circle outside the cylinder which makes sense to me, but I don't get how the current would be (r^2/R^2)*I where r is the radius of the circle of the ampere surface outside the cylinder.