How is real power defined in a single-phase AC circuit?

Real power in a single-phase AC circuit refers to the actual power consumed by the circuit to perform useful work. It is defined in terms of the portion of the current that is in phase with the voltage. When current flows in phase with voltage, it signifies that the power being utilized is effectively converted into work or used to produce heat, light, or other forms of energy.

The calculation for real power often involves the product of voltage, current, and the cosine of the phase angle between them, indicating that only the component of current which is in phase with the voltage contributes to the real power. This distinction is crucial in understanding power management in AC circuits, as it directly impacts efficiency and energy consumption.

The other options reflect different aspects of power in AC circuits, such as total power, which includes not only the real power but also reactive power, or reactive power itself, which does not do any useful work and is instead associated with energy storage in inductors and capacitors.