Problem 3.310

A long solenoid of cross-sectional radius \(a\) has a thin insulated wire ring tightly put on its winding; one half of the ring has the resistance \(\eta\) times that of the other half. The magnetic induction produced by the solenoid varies with time as \(B=b t,\) where \(b\) is a constant. Find the magnitude of the electric field strength in the ring.