Which devices are used in circuits to provide the type of reactance needed?

• A. Resistors
• B. Diodes
• C. Transformers
• D. Capacitors and Inductors

Answer: (D)

Reactance comes from energy-storage elements in an AC circuit. A capacitor stores energy in an electric field, giving capacitive reactance that decreases as frequency rises (X_C = 1/(ωC)). An inductor stores energy in a magnetic field, giving inductive reactance that increases with frequency (X_L = ωL). These two elements supply the reactive part of impedance, shaping how voltage and current relate in time and enabling tuning and filtering. Resistors don't create this reactive behavior; they dissipate real power and keep current and voltage in step. Diodes are nonlinear and aren’t used to provide a fixed reactance. Transformers involve inductance and coupling but the fundamental devices that provide the needed reactive effects are capacitors and inductors.