What is working principle of inductor?

Answer 1

A changing current through an inductor induces a voltage into the inductor, the direction of which always opposes the change in that current.

So, in a d.c. circuit, an inductor will oppose (not prevent) any rise or fall in current, although the magnitude of that current will be determined by the resistance of that inductor, not by its inductance.

In an a.c. circuit, because the current is continuously changing both in magnitude and in direction, it acts to continuously oppose the current due to its inductive reactance. Inductive reactance is proportional to the inductance of the inductor and the frequency of the supply. The vector sum of the inductive reactance of the inductor and the resistance of the inductor, is termed the impedance of the inductor. Inductive reactance, resistance, and impedance are each measured in ohms.