To practice Problem-Solving Strategy 30.1 Electromagnetic Induction. A coil of wire contains NNN turns and has an electrical resistance RRR. The radius of each turn is aaa. Initially, inside the coil there exists a uniform magnetic field of magnitude B0B0B_0 parallel to the axis of the coil. The magnetic field is then reduced slowly. The current induced in the coil is III. How long does it take for the magnitude of the uniform field to drop to zero