College Physics III – Thermodynamics, Electricity, and Magnetism

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Capacitive reactance

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College Physics III – Thermodynamics, Electricity, and Magnetism

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.

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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?
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