What is reactance in a capacitor?
Reactance in a Capacitor
Reactance in a capacitor, known as capacitive reactance, is the opposition that a capacitor offers to alternating current (AC). Unlike resistance, which opposes the flow of electrons directly, capacitive reactance opposes changes in voltage. This opposition is due to the capacitor's ability to store and release electrical energy in response to changes in voltage across it.
Key Characteristics of Capacitive Reactance
- Unit and Symbol: Capacitive reactance is measured in ohms and symbolized by (X_C).
- Relationship with Frequency: Capacitive reactance decreases as the frequency of the AC increases. This is opposite to inductive reactance, which increases with frequency.
- Phase Shift: In a pure capacitive circuit, the voltage lags the current by 90 degrees. This means the current leads the voltage.
- Formula: The formula for capacitive reactance is given by:
[
X_C = \frac{1}{2\pi fC}
]
where:
- (X_C) is the capacitive reactance in ohms,
- (f) is the frequency of the AC in hertz,
- (C) is the capacitance in farads.
Implications
- Energy Storage and Release: Capacitors do not dissipate power; they store and release energy alternately, resulting in a power wave that oscillates between positive and negative.
- Frequency Dependence: Higher frequencies result in lower reactance, allowing more current to flow through the capacitor for the same voltage.
Overall, capacitive reactance plays a crucial role in AC circuits, particularly in applications like filters and resonant circuits.