In a circuit where the AC voltage and current are out of phase, how can true power be determined?

In a circuit where the AC voltage and current are out of phase, the concept of true power (also known as real power) is crucially linked to the power factor, which is the cosine of the phase angle between the voltage and current waveforms. Since true power reflects the actual work done in the circuit, it is determined by the product of the apparent power (the product of the voltage and current, without considering phase differences) and the power factor, which accounts for the phase difference.

When apparent power—measured in volt-amperes (VA)—is multiplied by the power factor, it gives the true power in watts (W). This multiplication effectively narrows down the apparent power to represent only the portion that is actually doing useful work, as influenced by the current and voltage phase relationship.

This method is particularly important in AC circuits where reactive components, like inductors and capacitors, cause the voltage and current to be out of phase, resulting in a distinction between apparent and true power. Hence, using the power factor to adjust apparent power allows one to accurately calculate true power in such scenarios.