Inductance is the ratio of the magnetic flux of the wire to the current that produces the alternating flux in and around the wire when the alternating current passes through the wire.

When a DC current passes through the inductor, the magnetic field lines around it are only fixed and do not change with time.

But when an alternating current is passed through the coil, it will show magnetic field lines that change with time.

According to Faraday's Law of Electromagnetic Induction (MMI), a changing magnetic field line creates an induced potential at both ends of the coil, which acts as a "new source ".

When a closed loop is formed, this induced potential will produce an induced current.

The total amount of magnetic field lines generated by the induced current is known by Lenz's law in an attempt to keep the original field lines from changing.

As the original change of magnetic force line comes from the change of the external alternating power supply, the inductance coil has the property of preventing the current change in the alternating current circuit from the objective effect.

Inductance coils have similar properties to inertia in mechanics, which is called "self-induction" in electricity. Usually at the moment when the knife switch is opened or switched on, sparks will occur, which is caused by the phenomenon of self-induction that produces very high induced potential.

In short, when the inductance coil is connected to the AC power supply, the magnetic field lines inside the coil will change with the alternating current at all times, causing the coil to continuously produce electromagnetic induction.

The electromotive force generated by the change of the current of the coil itself is called "self-induced electromotive force ".

Thus, the inductance is only a parameter related to the number, size and shape of the coil and the medium, and it is a measure of the inertia of the inductance coil and has nothing to do with the applied current.

Inductance is good or bad in two ways:

1, inductance measurement: the multimeter hit the buzzer diode, put the pen on the two pins, see the reading of the multimeter.

2, good or bad judgment: for the patch inductance at this time the reading should be zero, if the multimeter reading is too large or infinite, it means the inductance is damaged.

For inductance coil turns more, the wire diameter of the thin coil reading will reach dozens of times hundreds, usually the coil of DC resistance is only a few ohm.

If the inductance coil is not seriously damaged and can not be determined, the inductance can be measured with the inductance meter or the replacement method can be used to judge.