Which statement best describes impedance?

• A. The total opposition to direct current, ignoring reactance
• B. The resistance of a circuit to heat
• C. The total opposition a circuit presents to alternating current, combining resistance and reactance
• D. The voltage drop across a conductor

Answer: (C)

Impedance is the total opposition to alternating current, combining resistance and reactance. In AC circuits, current and voltage interact with both the energy dissipated as heat (resistance) and the energy stored and returned by inductors and capacitors (reactance). Impedance is the overall effect of these two parts at a given frequency, and it dictates how much current flows for a given AC voltage. The description that it opposes DC and ignores reactance isn’t correct because impedance specifically describes behavior in AC, and reactance is part of that description. The idea of resistance to heat describes power loss, not the overall opposition to current. The voltage drop across a conductor is about voltage change along a path, not the total opposition described by impedance.