Reactance

Capacitive and inductive reactance opposing alternating current flow in circuit elements.

General idea of the topic

Reactance quantifies the opposition that capacitors and inductors present to alternating current, with a direct dependence on the frequency of the applied signal.

A capacitor offers lower reactance at high frequencies while an inductor does the opposite, and this asymmetry is the basis of filtering, reactive-power compensation and resonant circuit design.

What you will truly understand

• Why capacitive reactance decreases when frequency increases.
• Why inductive reactance increases when frequency increases.
• How phase and reactive power alter grid current.

Recommended learning route

1. Capacitive reactance.
2. Inductive reactance.
3. Comparison of both behaviors at a given frequency.

Physical criterion you must acquire

Do not treat capacitive and inductive reactances as fixed resistances: they are phase-dependent quantities that change with frequency.

Connection with real problems

Power-factor compensation, AC filters, motors and converters depend on this block.

Final goal of the topic

Calculate and justify reactances with physical criterion to integrate them correctly into AC circuits.