Power Factor is the relationship between the active power and the apparent power. The relationship between the types of power used to run a system is usually shown as a right-angled triangle. Real power is the capacity of the circuit for performing work in a particular time. Apparent power is the product of the current and voltage of the circuit. Active power is shown at right angles to reactive power, sometimes known as ‘waste’ because it is out-of-phase, and does no useful work.