A long vertical wire carries an unknown current. Coaxial with the wire is a long, thin, cylindrical conducting surface that carries a current of 75 mA upward. The cylindrical surface has a radius of 3.0 mm. Suppose that the magnitude of the magnetic field at a point 4.0 mm from the wire is 1.0 µT.
(a) What is the size of the current in the wire?
mA