Inductive Reactance

Formula

Description

Inductive reactance is the opposition an inductor presents to alternating current, and it increases linearly with both frequency and inductance. This is the opposite behavior of capacitive reactance, which decreases with frequency. The physical basis is Faraday's law: a changing current through the inductor creates a changing magnetic field, which induces a back-EMF that opposes the change. At DC (0 Hz) an ideal inductor is a short circuit with zero reactance, while at very high frequencies it approaches an open circuit.

Variables

• XL — Inductive reactance in ohms (Ω)
• f — Frequency in hertz (Hz)
• L — Inductance in henries (H)

Practical Notes

Inductive reactance causes voltage to lead current by 90 degrees, the exact opposite of capacitive reactance. This complementary behavior is what enables LC resonant circuits and is exploited in filter design, impedance matching, and power factor correction.