Reactance arises from which components?

• A. Resistors
• B. Inductance or Capacitance
• C. Batteries
• D. Transformers

Answer: (B)

Reactance is the part of impedance that comes from components that store energy, not from those that simply dissipate it. Inductors store energy in a magnetic field and have inductive reactance that grows with frequency (X_L = ωL). Capacitors store energy in an electric field and have capacitive reactance that decreases with frequency (X_C = 1/ωC). Together, these energy-storage elements are what make impedance have a reactive (imaginary) component and cause current and voltage to shift relative to each other.

Resistors just dissipate energy as heat and present a constant resistance, so they don’t create reactance. Batteries are energy sources, not impedance. Transformers involve magnetic coupling and behave inductively, but the core idea is that the energy-storage elements—inductance and capacitance—are the source of reactance.