Capacitive reactance

Definition

Capacitive reactance is the opposition that a capacitor offers to alternating current (AC), due to the phase difference between voltage and current. It is inversely proportional to both the frequency of the AC signal and the capacitance.

5 Must Know Facts For Your Next Test

1. Capacitive reactance ($X_C$) is given by the formula $X_C = \frac{1}{2\pi fC}$, where $f$ is the frequency and $C$ is the capacitance.
2. It has units of ohms (Ω), similar to resistance.
3. As frequency increases, capacitive reactance decreases, making capacitors more effective at filtering high-frequency signals.
4. In a purely capacitive circuit, current leads voltage by 90 degrees.
5. Capacitive reactance plays a key role in determining the impedance of AC circuits containing capacitors.

Review Questions

• What happens to capacitive reactance as the frequency of an AC signal increases?
• How does capacitive reactance differ from resistance in terms of phase relationship between voltage and current?
• What is the formula for calculating capacitive reactance?

Related terms

Inductive Reactance: The opposition that an inductor offers to alternating current (AC), proportional to both frequency and inductance.

Impedance: The total opposition that a circuit offers to AC, combining resistive, inductive, and capacitive effects.

Phase Angle: The angular difference in phase between the voltage across an element and the current through it in an AC circuit.