Page 317 - Basic Electrical Engineering

Now, the second term is a cosine term whose average value over a complete
cycle is zero.

Hence, the average power consumed is

Figure 3.21 power triangle diagram

P = V rms × I rms cos ϕ = VI cos ϕ W
av

Power factor

It may be defined as the cosine of the phase angle between the voltage and

current; cos ϕ is known as power factor. Power factor can also be expressed
as the ratio, R/Z = resistance/impedance = cos ϕ