When analyzing a coaxial cable and trying to find the B field in the space betwen the outer and inner cables, using ampere's law the B field will be depedent only upon the current running through the inner wire. Why is this? I know that yes Ampere's law says that only the current contained within the amperean loop can cause a B field, but i want a better explanation then that. Lets suppose there was just a plain hollow cylindrical conductor with current running through it. Would there be a B field running through it?