| for a passive linear two-terminal element or two-terminal circuit with terminals A and B under sinusoidal conditions, quotient of the phasor representing the voltage (131-11-56) between the terminals by the phasor representing the electric current in the element or circuit |
where the sinusoidal voltage represented by the phasor is the difference of the electric potentials at A and at B, and where the sinusoidal electric current represented by the phasor is taken positive if its direction is from A to B and negative if its direction is from B to A
Note 1 to entry: The impedance of an element or circuit is the inverse of its admittance. It is equal to , where R is resistance to alternating current, X is reactance, Z is apparent impedance, and φ is displacement angle.
Note 2 to entry: With a suitable qualifier, the word impedance is used to form composite terms designating quantities of the same kind as impedance, e.g.: transfer impedance, characteristic impedance.
Note 3 to entry: The coherent SI unit of impedance is ohm, Ω.