How do capacitors and inductors affect alternating current at different frequencies?

In electrical engineering, capacitors and inductors exhibit frequency-dependent opposition to alternating current, known as reactance.

Inductive Reactance

Inductors oppose changes in current. The opposition they provide, called inductive reactance ($X_L$), is directly proportional to the frequency ($f$) of the current and the inductance ($L$) of the component, expressed as:
$$X_L=2\pi fL$$
As frequency increases, the inductor’s opposition to the current increases. Consequently, inductors allow lower-frequency currents to pass more easily than higher-frequency currents.1

Capacitive Reactance

Capacitors oppose changes in voltage. The opposition they provide, called capacitive reactance ($X_C$), is inversely proportional to the frequency of the current and the capacitance ($C$) of the component, expressed as:
$$X_C=\frac{1}{2\pi fC}$$
As frequency increases, the capacitive reactance decreases. Therefore, capacitors allow higher-frequency currents to pass more readily, while offering greater opposition to lower-frequency currents.12

In summary, inductors act as high-frequency blockers, while capacitors act as high-frequency conductors in alternating-current circuits.12