A very long coaxial cable consists of a solid cylindrical inner conductor of radius {R_1} surrounded by an outer cylindrical conductor with inner radius {R_2} and outer radius {R_3}. The region between the two conductors is filled with a waxlike insulating material to keep the conductors from touching each other.
Part A: If the inner and outer conductors carry equal currents I in opposite directions, use Ampère's law to derive an expression for the magnetic field as a function of r (the distance from the central axis) at points BETWEEN the two conductors ({R_1}
Part B: If the inner and outer conductors carry equal currents I in opposite directions, use Ampère's law to derive an expression for the magnetic field as a function of r (the distance from the central axis) at points OUTSIDE the cable (r>{R_3}).