• noun a measurement of the effect an electrical circuit or cable has on signal current magnitude and phase when a steady voltage is applied.


  • Measured in ohms, the total opposition or resistance to the flow of current when voltage is applied to an alternating current electric circuit.


  • Its symbol is Z. The total opposition a circuit or device offers to the flow of AC. It is a complex quantity, whose real number component is resistance, and whose imaginary number component is reactance. Its formula is: Z = R +jX, in which Z is the impedance, R is the resistance, X is the reactance, and j is the square root of -1. That is, j2 = -1. Z is expressed in ohms. Also called electrical impedance.