impendance

Impendance is a term most often encountered as a misspelling of impedance. In electrical engineering, impedance, denoted Z, is the complex opposition that a circuit presents to alternating current. It combines resistance R and reactance X: Z = R + jX, where R is real and X is imaginary. Reactance arises from energy storage in magnetic and electric fields. Inductive reactance X_L = ωL increases with frequency; capacitive reactance X_C = -1/(ωC) decreases with frequency. The magnitude is |Z| = sqrt(R^2 + X^2) and the phase angle is φ = arctan(X/R).

In AC circuits, impedance generalizes Ohm's law to V = I Z, and current I = V/Z. Impedance adds to facilitate analysis of series and parallel networks using complex arithmetic. Admittance Y = 1/Z is the reciprocal quantity. Impedance depends on frequency, so circuit behavior changes with signal frequency. Impedance matching, by adjusting impedances at interfaces, optimizes power transfer and reduces reflections in transmission lines. Common reference impedances include 50 ohms for RF, 75 ohms for video, and other standards used in communications.

Measurement and applications: Instruments such as LCR meters, impedance analyzers, and vector network analyzers quantify Z across frequencies. Impedance concepts extend beyond electronics to acoustics and mechanics where reactance-like terms describe the opposition to oscillatory motion.

Terminology: The preferred term is impedance; impendance is rarely used in technical writing and is typically considered a misspelling. See also impedance spectroscopy, admittance, reactance, resistance, impedance matching.