Type of wire coil toroidal winding machine 9

Inductance is the ratio of the magnetic flux of the conductor to the current producing the alternating magnetic flux generated in and around the conductor when the alternating current passes through the conductor.

When DC current passes through the inductor, only fixed magnetic lines of force appear around it, which does not change with time; However, when AC current passes through the coil, there will be magnetic lines of force around it that change with time. According to Faraday's law of electromagnetic induction - magnetoelectricity, the changing magnetic lines of force will produce induced potential at both ends of the coil, This induced potential is equivalent to a "new power supply" ". when a closed loop is formed, the induced potential will generate induced current. According to Lenz's law, the total amount of magnetic lines of force generated by the induced current should try to prevent the change of the original magnetic lines of force. Since the change of the original magnetic lines of force comes from the change of external alternating power supply, from the objective effect, the inductive coil has the characteristics of preventing the change of current in AC circuit. The inductive coil has the characteristics of The characteristic of inertia in mechanics is similar. It is called "self induction" in electricity. Usually, sparks will occur at the moment when the knife switch is opened or turned on. This 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 line inside the coil will change with the alternating current, resulting in the continuous electromagnetic induction of the coil. This electromotive force generated by the change of 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 turns, size, shape and medium of the coil. It is a measure of the inertia of the inductance coil and has nothing to do with the applied current.