Reactance and frequency

In many ways capacitive reactance behaves like a mirror image of inductive reactance. But in another sense, X_C is an extension of X_L into negative values—below zero. If the frequency of an ac source is given in hertz as f and the capacitance of a capacitor in farads as C, then the capacitive reactance is

X_C = 1/(6.28fC)

This same formula applies if the frequency, f, is in megahertz and the capacitance, C, is in microfarads (μF). Just remember that if the frequency is in millions, the capacitance must be in millionths.
Capacitive reactance varies inversely with the frequency. This means that the function X_C vs f appears as a curve when graphed, and this curve “blows up” as the frequency nears zero.
Capacitive reactance also varies inversely with the actual value of capacitance, given a fixed frequency. Therefore, the function of X_C vs C also appears as a curve that “blows up” as the capacitance approaches zero.
The negative of Xc is inversely proportional to frequency, and also to capacitance. Relative graphs of these functions are shown in Fig. 1.

Fig. 1: Capacitive reactance is negatively, and inversely, proportional to frequency (f) and also to capacitance (C).