Walker, Halliday & Resnick — Induction and Inductance: Problem 47

47 A long solenoid has a diameter of 12.0 cm. When a current i exists in its windings, a uniform magnetic field of magnitude B = 30.0 mT is produced in its interior. By decreasing i, the field is caused to decrease at the rate of 6.50 mT/s. Calculate the magnitude of the induced electric field (a) 4.20 cm and (b) 10.3 cm from the axis of the solenoid.