Reactance is a measure of the opposition that a circuit or component offers to the flow of alternating current (AC).
It is similar to resistance, which is the opposition to the flow of direct current (DC), but reactance only applies to AC circuits.
Reactance is caused by the storage and release of energy by certain circuit components, such as capacitors and inductors.
Capacitors store energy in an electric field and release it back to the circuit, while inductors store energy in a magnetic field and release it back to the circuit.
The effect of this energy storage and release is to cause the circuit to oppose the flow of current.
It is measured in ohms, just like resistance, but it is designated with the symbol X instead of R.
The total impedance of a circuit is the combination of its resistance and reactance and is measured in ohms as well.
The value of it in a circuit depends on the frequency of the AC being used and the values of the circuit components.
Reactance can be positive or negative, depending on the phase relationship between the voltage and current in the circuit. Positive reactance means that the current lags the voltage, while negative means that the current leads the voltage.