Which electrical characteristic opposes the flow of alternating current?

• A. Conductance
• B. Reactance
• C. Resistance
• D. Impedance

Answer: (D)

When alternating current moves through a circuit, the overall opposition it faces is called impedance. Impedance combines two ideas: resistance, which always opposes current and dissipates energy as heat, and reactance, which arises from inductors and capacitors and stores energy (charging and discharging) in a way that depends on frequency. The magnitude of impedance determines how much current the voltage can push, while the phase angle shows whether the current lags or leads the voltage.

Resistance alone is constant with respect to frequency and doesn’t account for energy storage. Reactance alone describes the energy-storage part but not the total opposition. Conductance is simply how easily current flows (the reciprocal of resistance) and isn’t the overall opposition. Impedance, the combination of resistance and reactance, is the correct term for the total opposition to AC flow.