# Electrical Impedance

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## Electrical impedance

The measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current (ac) circuit.

A generalized ac circuit may be composed of the interconnection of various types of circuit elements. The impedance of the circuit is given by *Z* = *V*/*I*, where *Z* is a complex number given by *Z* = *R* + *j**X*. *R*, the real part of the impedance, is the resistance of the circuit, and *X*, the imaginary part of the impedance, is the reactance of the circuit. The units of impedance are ohms. *See* Electrical resistance, Reactance

## Impedance, Electrical

a quantity characterizing the opposition presented by a circuit to an alternating current. Often called simply impedance, it is measured in ohms. In the case of a sinusoidal alternating current, the impedance is expressed by the ratio of the amplitude of the voltage applied to the circuit terminals and the amplitude of the current throught the circuit; here, the impedance is equal to , where *r* is the resistance and *x* is the reactance. In the case of a nonsinusoidal alternating current, the impedance is determined separately for each kth har monic component: .