The term load impedance under maximum power transfer refers to what relationship to source impedance?

• A. The complex combination of resistance and reactance seen by the source
• B. Only the resistive part of the load
• C. Only the reactive part of the load
• D. The source impedance itself

Answer: (A)

In AC circuits, impedance has both a real part (resistance) and an imaginary part (reactance). The load impedance under maximum power transfer is the complex impedance as seen by the source, and for maximum real power transfer it should be the complex conjugate of the source impedance. This conjugate match cancels the reactive portion from the source’s view, making the current and voltage in phase so the power delivered is real rather than circulating as reactive energy. So the load impedance is the full complex combination of resistance and reactance seen by the source, not just the resistive part, not just the reactive part, and not the source impedance itself.