What is the role of reactance in a circuit?

• A. It determines the color of the capacitor.
• B. It signifies the real power consumption.
• C. It is the DC resistance.
• D. It represents energy storage and contributes to impedance by creating a reactive (imaginary) component.

Answer: (D)

Reactance is the part of circuit opposition that comes from energy storage elements in AC signals. It doesn’t dissipate power like resistance; instead, capacitors store energy in an electric field and inductors store energy in a magnetic field, and this storage shows up as a reactive (imaginary) component of impedance. The impedance of a circuit can be written as Z = R + jX, where the real part R handles real power loss and the imaginary part X (the net reactance) captures the energy-storage effects. Inductive reactance X_L = ωL increases with frequency, while capacitive reactance X_C = 1/(ωC) decreases with frequency. This frequency-dependent behavior and the resulting phase difference between voltage and current are the essence of reactance’s role.