NEIEP Electrical Theory And Application (430) Practice Exam

In AC circuit power calculations, what does cosφ represent?

Power factor Efficiency Phase angle Impedance value

Correct Answer:

Power factor

Explanation:

Cosφ is the power factor. It’s the ratio of real power to apparent power (cosφ = P/S) and also the cosine of the phase angle between voltage and current. This tells you how effectively the supplied power is doing useful work. If the voltage and current are in phase (φ = 0), cosφ = 1, meaning all the power is real power. As φ grows due to inductive or capacitive effects, cosφ drops, and some power becomes reactive rather than doing useful work. It’s not a measure of efficiency, nor the phase angle itself (that would be φ), nor the impedance value.

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