Real power in an AC circuit is defined as the product of the applied voltage and the current that is in phase with the voltage. Which option expresses this correctly?

Real power in an AC circuit is defined as the product of the applied voltage and the current that is in phase with the voltage. Which option expresses this correctly?

• A. Real power equals RMS voltage times RMS current
• B. Real power equals peak voltage times peak current
• C. Real power equals RMS voltage times the current in phase with voltage
• D. Real power equals the product of applied voltage and the current that is in phase with the voltage

Answer: (D)

Real power is the portion of electrical power that actually does work, and it comes from the current that flows in step with the voltage. Only the in-phase component of current can deliver energy to a load on average, so the average power is the product of the voltage and that in-phase current. In formula terms, P equals Vrms times Irms times cos(phi), which is the same as Vrms times the in-phase component of current. Saying that real power is the product of the applied voltage and the current in phase with the voltage directly expresses this idea, making it the correct description. The other options either use peak values (which do not represent average power), or mix in the total current (including reactive parts) with voltage, which gives apparent power rather than real power.

Real power is the portion of electrical power that actually does work, and it comes from the current that flows in step with the voltage. Only the in-phase component of current can deliver energy to a load on average, so the average power is the product of the voltage and that in-phase current. In formula terms, P equals Vrms times Irms times cos(phi), which is the same as Vrms times the in-phase component of current. Saying that real power is the product of the applied voltage and the current in phase with the voltage directly expresses this idea, making it the correct description. The other options either use peak values (which do not represent average power), or mix in the total current (including reactive parts) with voltage, which gives apparent power rather than real power.