22.4 Capacitive Reactance

In a DC circuit, there is no current through a capacitor -- or through this simple circuit that contains a capacitor.

In a simple resistor circuit, we defined resistance R by

V = I R

In a similar fashion, we can write


where VC is the maximum voltage across the capacitor and I is the maximum current through the circuit. XC is called the "capacitive reactance"; it is analogous to resistance and is also measured in ohms (). The "capacitive reactance", XC, is given by

XC, the "Capacitive Reactance" plays a role very similar to that of R, the resistance. The capacitive reactance is a measure of how difficult it is for current to flow. With AC circuits, this depends upon the frequency.

rms Values

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Inductive Reactance

(c) Doug Davis, 2002; all rights reserved