Reactance is the opposition that an electrical component gives to the flow of alternating current (AC). It’s similar to resistance but works differently because it only happens in AC circuits.
Reactance comes in two types:
Inductive reactance happens because an inductor (a coil of wire) creates a magnetic field when current flows through it. This magnetic field resists changes in the current.
The formula is:
Where:
Key Points:
Example: If you have an inductor with 0.1 H inductance in a circuit running at 50 Hz, the inductive reactance is:
Capacitive reactance occurs because a capacitor resists changes in voltage by storing and releasing energy in an electric field.
The formula is:
Where:
Key Points:
Example: A 10 μF capacitor in a circuit at 60 Hz has this reactance:
| Property | Inductive Reactance (XL) | Capacitive Reactance (XC) |
| Depends on | Frequency and inductance | Frequency and capacitance |
| Formula | ||
| Frequency Effect | Increases with frequency | Decreases with frequency |
| Phase Relationship | Current lags voltage by 90° | Current leads voltage by 90° |
In Series: The total reactance is:
(Subtract because they oppose each other.)
In Parallel: The total reactance is calculated using:
When the inductive reactance (XL) equals the capacitive reactance (XC), the circuit is in resonance. At this point:
Because of its inductance and capacitance, an electrical reactance is described as a flow in a circuit element that flows in the opposite direction of the current. For the same applied voltage, if the reactance is higher, the current will be lower. Although reactance is quite similar to electric resistance, it varies in a few areas. When an alternating current passes through an electric circuit or element, both the phase and amplitude of the current change. In addition, the energy is stored in the reactance-containing element.
This consequence is known as REACTANCE, and it is denoted by the letter X and stated as X = XL XC or X = XC X L. In a circuit with 50 ohms inductive reactance and 25 ohms capacitive reactance in series, the net reactance, or X, is 50 ohms 25 ohms, or 25 ohms inductive reactance.