Which of the following terms refers to the efficiency of power usage in a circuit?

The term that refers to the efficiency of power usage in a circuit is power factor. Power factor is a dimensionless number between 0 and 1 that represents the ratio of real power (the actual power consumed by the devices) to apparent power (the total power flowing in the circuit). It indicates how effectively electrical power is being converted into useful work output.

When power factor is close to 1, it signifies that most of the power is being used effectively, with minimal energy wasted in the form of reactive power. A low power factor indicates inefficiencies in the system where a significant proportion of power does not contribute to useful work, often because of inductive loads that require additional reactive power to operate.

Thus, understanding power factor is crucial in evaluating or designing electrical systems to ensure efficient power usage and reduce energy costs.