Impedance

—The total opposition in an electric circuit to the flow of an alternating current; being made up of the actual or ohmic resistance. and the apparent resistance due to self-induction. The self-induction part of the impedance offered - by a coil varies with the rate at which lines of force cut the convolutions; that is to say, it varies with the rate of alternation, and also with the amplitude and shape of the. current wave. If an alternating current be applied to a coil having a resistance of R ohms and a coefficient of self induction of L henries, when the current curve follows the sine law, the Impedance = A/R? + p2 L2 in which, p = 2Tn, where n represents the number of complete alternations per second.