Reactance of a Coil

As in the case of a capacitor, the current and voltage of an ideal inductor coil (i.e. one with no active resistance) are displaced in phase by 90°, resulting in purely reactive power. The coil's higher AC resistance compared with its DC resistance is due to the inductive reactance X L. This reactance arises from an opposing, self-induced voltage.

The higher the inductance L of a coil, the higher the opposing voltage and resulting reactance. Also, the faster the change in current - i.e. the higher the frequency - the higher the induced voltage. The formula for inductive reactance is:INDUCTORS IN AC CIRCUITS

In qualitative terms:

The higher the frequency and inductance, the larger the inductive reactance.

Example 1: at a frequency of 50 Hz, a coil with an inductance of 2 H has the following reactance


Example 2: at a frequency of 40 Hz, a coil with a reactance of 12.5 W has the following inductance


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