What does the power factor represent in an AC circuit?

The power factor in an AC circuit represents the ratio of true power to apparent power. True power, measured in watts, reflects the actual power consumed by the circuit to perform useful work, such as lighting a bulb or operating a motor. Apparent power, measured in volt-amperes, represents the total power flowing in the circuit, combining both true power and reactive power.

This ratio is crucial because it helps determine the efficiency of a circuit. A power factor of 1 (or 100%) indicates that all the power is being used effectively. In contrast, a power factor less than 1 shows that some of the power is reactive and not being converted into useful work, which can lead to inefficiencies in the system.

Understanding the power factor is essential for optimizing energy consumption and minimizing energy costs in AC circuits, making it a key concept in electrical engineering and power management. The other options, while related to electrical concepts, do not accurately describe what the power factor signifies in an AC circuit.