Problem 3.326

A closed circuit consists of a source of constant emt \(\mathscr{B}\) and a choke coil of inductance \(L\) connected in series. The active resistance of the whole circuit is equal to \(R .\) At the moment \(t=0\) the choke coil inductance was decreased abruptly \eta times. Find the current in the circuit as a function of time \(t\).

Instruction. During a stepwise change of industance the total magnetic flux (flux linkage) remains constant.