Electrical impedance

Electrical impedance is the frequency-dependent opposition a circuit presents to alternating current, combining resistance and reactance as a complex quantity.

Ohm's law: Ohm's law relates voltage, current, and resistance in an electrical circuit. Impedance generalizes the voltage–current relation of Ohm’s law to alternating signals.
Alternating current: Alternating current periodically reverses direction, unlike direct current. Impedance describes circuit opposition specifically for alternating current.
RLC circuit: An RLC circuit contains resistors, inductors, and capacitors connected in series or parallel. Its impedance varies with frequency and can produce resonance.
Electrical admittance: Electrical admittance measures how readily a circuit permits alternating current and is the reciprocal of impedance. It describes the same voltage–current relation from the opposite direction.
Resistance: Resistance is the opposition to electric current that dissipates electrical energy as heat. It forms the real, energy-dissipating part of impedance.
Frequency: Frequency is the number of cycles of a repeating event per unit time. Capacitive and inductive reactance vary with the frequency of the applied signal.
Electrical resonance: Electrical resonance occurs when inductive and capacitive effects cancel at a particular frequency. At resonance, circuit impedance can reach a minimum or maximum depending on its configuration.
Direct current: Direct current flows in one direction and has constant polarity. At steady state, ideal capacitors and inductors behave differently than under alternating current.
Reactance: Reactance is the opposition to alternating current caused by capacitance or inductance. It forms the imaginary, energy-storing part of impedance.
Capacitor: A capacitor stores energy in an electric field between conductors separated by an insulator. Its reactance decreases as signal frequency increases.

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