Reactance is a measure of how a circuit component resists the flow of alternating current (AC) due to its inductive or capacitive properties. Unlike resistance, which opposes both direct current (DC) and AC, reactance specifically opposes changes in current or voltage in AC circuits. Reactance is an essential aspect of the impedance in AC circuits and has two primary types: inductive reactance and capacitive reactance.
1. Inductive Reactance ((X_L)):
- Source: Comes from inductors in a circuit.
- Characteristics: Inductive reactance increases with frequency. This means that an inductor will oppose changes in current more strongly at higher frequencies.
- Formula: The inductive reactance ((X_L)) of an inductor is given by:
[ X_L = 2\pi fL ]
Where: - ( f ) is the frequency of the AC source in hertz (Hz).
- ( L ) is the inductance of the inductor in henrys (H).
2. Capacitive Reactance ((X_C)):
- Source: Comes from capacitors in a circuit.
- Characteristics: Capacitive reactance decreases with frequency. This means a capacitor will oppose changes in voltage more strongly at lower frequencies.
- Formula: The capacitive reactance ((X_C)) of a capacitor is given by:
[ X_C = \frac{1}{2\pi fC} ]
Where: - ( f ) is the frequency of the AC source in hertz (Hz).
- ( C ) is the capacitance of the capacitor in farads (F).
Key Points:
- Unit: The unit of reactance (both inductive and capacitive) is ohms ((\Omega)), the same as resistance.
- Phasor Representation: In phasor diagrams, inductive reactance is represented with a phase angle of +90° (leading the current), while capacitive reactance has a phase angle of -90° (lagging the current).
- Impact on Circuit: In a purely reactive circuit (one with only capacitors or inductors), the voltage and current are out of phase by 90°. In circuits with both resistance and reactance, the phase difference will be somewhere between 0° and 90°, depending on the relative magnitudes of resistance and reactance.
Conclusion:
Reactance is a fundamental concept in AC circuit analysis, influencing how components like capacitors and inductors interact with AC voltage sources. Understanding reactance helps in designing and analyzing circuits, especially in applications like filtering and impedance matching.