I just have a quick question about how to use Ampere's Law. It says that ∫B ds = u0(i_enc), which I suppose is easy enough to understand. But I'm having trouble reconciling it with the notion of, say, the magnetic field at the center of a loop of wire. The magnetic field at the center of a loop of wire is B = (u0 * i) / (2R). But what if I were to draw an Amperian loop inside the loop of wire? Not enclosing the loop itself, but just an arbitrary circle within the loop's boundaries. From Ampere's Law, there's no i_enc here, which makes the right side of Ampere's Law equal to 0, which implies there is no magnetic field. And yet the earlier formula says that there is a magnetic field here, and we know there is. So clearly, I'm either using Ampere's Law wrong, or it's not applicable here. I'm not sure. Help is appreciated!