When calculating power in a reactive or inductive AC circuit, the true power is

When calculating power in a reactive or inductive AC circuit, the true power is

• A. equal to the apparent power
• B. less than the apparent power
• C. greater than the apparent power
• D. undefined

Answer: (B)

In AC circuits, energy can be described as real (true) power, apparent power, and reactive power. Real power is the average work actually done per unit time, while apparent power is simply the product of the RMS voltage and RMS current. Reactive power represents energy that gets stored and then returned by reactive elements like inductors. When a circuit is inductive, the current lags behind the voltage by a phase angle φ. The real power is P = VI cos φ, whereas the apparent power is S = VI. Because cos φ is less than 1 when there’s a phase difference, the real power is smaller than the apparent power. In a purely inductive circuit, cos φ is zero and real power is zero, which is still less than the apparent power. In a purely resistive circuit, cos φ is 1 and real power equals apparent power. The key idea is that the phase difference in reactive circuits causes the true power to be less than the apparent power.

In AC circuits, energy can be described as real (true) power, apparent power, and reactive power. Real power is the average work actually done per unit time, while apparent power is simply the product of the RMS voltage and RMS current. Reactive power represents energy that gets stored and then returned by reactive elements like inductors.

When a circuit is inductive, the current lags behind the voltage by a phase angle φ. The real power is P = VI cos φ, whereas the apparent power is S = VI. Because cos φ is less than 1 when there’s a phase difference, the real power is smaller than the apparent power. In a purely inductive circuit, cos φ is zero and real power is zero, which is still less than the apparent power. In a purely resistive circuit, cos φ is 1 and real power equals apparent power. The key idea is that the phase difference in reactive circuits causes the true power to be less than the apparent power.