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
- 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.
- It has units of ohms (Ω), similar to resistance.
- As frequency increases, capacitive reactance decreases, making capacitors more effective at filtering high-frequency signals.
- In a purely capacitive circuit, current leads voltage by 90 degrees.
- 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?
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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.
