Rahul Chopra

In AC circuits, "impedance" generalizes "resistance" by Anon User is a sensible statement giving the angle they are trying to get at, but slightly misleading in my opinion, i would personally say people use Resistance to generalise Impedance. I would like to clarify further the differences for you, in a more simplistic way, this helped me understand fundamental principles early. Resistance is the opposition of electrical current flow. Resistance occurs in AC & DC circuits. In addition to Resistance, AC circuits also exhibit Reactance. Reactance is also the opposition to electrical current flow. By its very nature a DC circuit will not exhibit any form of Reactance, therefore opposition to current flow will always be measured in Resistance. Reactance exists in two forms, Capacitive & Inductive. the combination of Reactance & Resistance is called Impedance Impedance can therefore be thought of as the opposition of electrical current flow in a AC circuit. Due to the nature of AC circuits Reactance is always present (even if only in infinitesimal amounts) Any measurement of the opposition of current flow in an AC circuit will always be measured in Impedance. Impedance & Resistance are both measured in Ohms, and are interchangeable in many electrical formulas in practice i.e, Ohms Law. As a simplistic general view, Impedance can be thought of as Resistance in an AC circuit.