A closed circuit consists of a source of constant emf and a choke coil of inductance L

Question:

A closed circuit consists of a source of constant emf ε 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 η times. Find the current in the circuit as a function of time t. Instruction. During a stepwise change of inductance the total magnetic flux (flux linkage) remains constant.