A very long, hollow cylinder (radius 2.1cm) is formed by rolling up a thin sheet of copper. Electric charges flow along the copper sheet parallel to the axis of the cylinder. The arrangement is, in effect, a hollow tube of current 3.5A. Use Ampère's law to find the magnetic field (a) outside the cylinder at a distance 4.9cm from the axis and (b) inside the cylinder at a distance 0.72cm from the axis. (Hint: For closed paths, use circles perpendicular to and centered on the axis of the cylinder.)

A very long, hollow cylinder (radius 2.1cm) is formed by rolling up a thin sheet of copper. Electric charges flow along the copper sheet parallel to the axis of the cylinder. The arrangement is, in effect, a hollow tube of current 3.5A. Use Ampère's law to find the magnetic field (a) outside the cylinder at a distance 4.9cm from the axis and (b) inside the cylinder at a distance 0.72cm from the axis. (Hint: For closed paths, use circles perpendicular to and centered on the axis of the cylinder.)