reaktansen

Reaktanse, also spelled reaktansi in some languages, is a concept in electrical engineering that describes the opposition a circuit presents to alternating current due to energy storage in inductors and capacitors. It is the imaginary component of impedance and is measured in ohms. In AC circuits, reaktanse is what causes current and voltage to be out of phase, without dissipating energy as heat.

The reactance of inductors and capacitors depends on frequency. Inductive reactance is X_L = ωL = 2πfL, meaning it grows with frequency. Capacitive reactance is X_C = 1/(ωC) = 1/(2πfC), meaning it falls as frequency rises. The net reactance of a circuit is X = X_L − X_C. In a circuit with resistance R and reactance X, the impedance is Z = R + jX. If X > 0, the circuit behaves predominantly inductively; if X < 0, it behaves predominantly capacitively. At a frequency where X = 0, the impedance is purely resistive and the circuit is at resonance (as in a series LC circuit with a resistor).

Reaktanse is distinct from resistance, the real part of impedance that dissipates energy as heat. While resistance remains constant with frequency in many components, reactance varies with frequency, enabling tuning, filtering, and impedance matching in a wide range of applications, such as radio receivers, audio electronics, and power systems.

Terminology varies by language; some refer to the same concept as reaktansi or reaktanse. In English, the term is reactance. See also impedance, resonance, and frequency-dependent circuit behavior.