Inductance is the ratio of the magnetic flux of the wire to the current used to produce the alternating magnetic flux generated in and around the wire when an alternating current passes through the wire.
When a DC current is passed through the inductor, only a fixed magnetic field line appears around it, which does not change with time; However, when an alternating current is passed through the coil, magnetic field lines that change with time appear around it. According to Faraday's law of electromagnetic induction, magnetic electricity, the changing magnetic field lines generate an induced electric potential at both ends of the coil, which is equivalent to a "new power source". When a closed loop is formed, this induced potential generates an induced current. From Lenz's law, we know that the total amount of magnetic field lines generated by the induced current should try to prevent the change of the original magnetic field lines. Since the original change of magnetic field lines comes from the change of the external alternating power supply, from the objective effect, the inductance coil has the characteristic of preventing the current change in the AC circuit. The inductance coil has similar characteristics to the inertia in mechanics, and is named "self-induction" in electricity, usually at the moment when the knife switch is opened or turned on, a spark will occur, which is caused by the high induced potential generated by the self-induction phenomenon.
In short, when the inductance coil is connected to the AC power supply, the magnetic field lines inside the coil will change all the time with the alternation of current, resulting in continuous electromagnetic induction in the coil. This electromotive force, which is generated by the change in the current of the coil itself, is called "self-induced electromotive force".
It can be seen that the inductance is only a parameter related to the number of coils, size, shape and medium of the coil, and it is a measure of the inertia of the inductor coil and has nothing to do with the impressed current.
