How much  of the power is true?

The above formulas allow you to figure out, given the resistance, reactance, and VA power, how many watts are real powers, and how many watts is imaginary or reactive power. This is significant in radio frequency denoted by RF equipment, as RF watt meters will display VA power, and reading can be exaggerated when there is reactance in the circuit.

Problem: 

A circuit has resistance of 50 O and 30 O of inductive reactance in series. A wattmeter shows 100 watts, depicting VA power. What is the value true power?

First, calculate power factor. You might use either phase angle method or the R/Z method. Assume that you use the phase angle method, then,

Phase angle= arctan =(X/R)

= arctan (30/50) =31 °

The power factor is cosine of phase angle. Therefore,

PF = cos 31 = 0.86 = 86 %

Remember that PF = P_T/P_VA. This means that true power, P_T, is 86 watts.