How is power factor defined?

Power factor is fundamentally defined as the ratio of real power to apparent power in a circuit. Real power, measured in watts, represents the actual power consumed by the circuit to perform work, while apparent power, measured in volt-amperes (VA), signifies the total power that flows through the system. The power factor is a dimensionless number, typically expressed as a value between 0 and 1, or as a percentage.

A high power factor indicates that a large proportion of the current is being used for productive work, thus leading to higher efficiency. Conversely, a low power factor signifies that a greater portion of the power is reactive power, which does not perform any useful work but contributes to the overall current flow.

In contrast to other choices, the ratio of current to voltage is not a correct definition of power factor. Moreover, the maximum load a circuit can handle relates to the circuit's design and safety limits rather than its efficiency or performance as defined by the power factor. Lastly, total power consumption of an entire facility encompasses all electrical usage and does not specifically pertain to the relationship between real and apparent power, which is essential to calculating the power factor.