Capacitive reactance

Definition

Capacitive reactance is the opposition that a capacitor presents to alternating 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 $X_C = \frac{1}{2\pi f C}$, where $f$ is the frequency in hertz and $C$ is the capacitance in farads.
2. The unit of capacitive reactance is ohms (Ω).
3. As frequency increases, capacitive reactance decreases.
4. Capacitive reactance causes a phase shift where the current leads the voltage by 90 degrees in an ideal capacitor.
5. In AC circuits, capacitive reactance impacts the total impedance.

Review Questions

• What happens to capacitive reactance when the frequency of an AC signal increases?
• How do you calculate capacitive reactance for a given frequency and capacitance?
• What phase relationship does capacitive reactance create between current and voltage?

Related terms

Inductive Reactance: The opposition that an inductor presents to alternating current, proportional to both frequency and inductance. It causes current to lag behind voltage by 90 degrees.

Impedance: The total opposition that a circuit presents to alternating current, composed of both resistance and reactance.

Capacitance: \(The ability of a system to store charge per unit voltage; measured in farads (F).\)