In AC circuits, certain components called inductors and capacitors add a special kind of resistance to the circuit known as Reactance.

Reactance is added to the resistance of a circuit to give what is known as impedance. This is still measured in Ohms, but is given the symbol Z.

An inductor is basically a coil of wire around a ferrite core and has an inductance measured in Henrys (H) and given the electrical symbol L. An inductor has a reactance that increases with the supply frequency.