The reactance of an alternating current (AC) circuit is inversely related to the frequency of the current.

Reactance is defined as the opposition that a circuit presents to the flow of electric current, arising from the presence of capacitive or inductive components. In an AC circuit, the reactance is frequency-dependent: it varies as the frequency of the alternating current changes. Specifically, the reactance of a capacitor decreases with increasing frequency, whereas the reactance of an inductor increases with increasing frequency.

The reactance of a capacitor, denoted as $X_C$, can be expressed using the formula:

where $f$ represents the frequency and $C$ denotes the capacitance. As the frequency $f$ increases, the reactance $X_C$ decreases. This occurs because, at higher frequencies, the capacitor is able to charge and discharge more rapidly, thus permitting greater current flow through the circuit.

Conversely, the reactance of an inductor, denoted as $X_L$, is given by the formula:

where $L$ is the inductance. In this case, as the frequency $f$ increases, the reactance $X_L$ also increases. This happens because, at higher frequencies, the inductor opposes changes in current more vigorously, which limits the amount of current that can flow through the circuit.

In summary, while the reactance of a capacitor decreases with increasing frequency, the reactance of an inductor increases. This leads to an overall change in the reactance of the circuit itself, highlighting the important relationship between reactance and frequency in the design and analysis of AC circuits.