If the phase angle between voltage and current is 0 degrees, what is the power factor?

If the phase angle between voltage and current is 0 degrees, what is the power factor?

• A. -1
• B. 0
• C. 1
• D. 0.5

Answer: (C)

Power factor is the cosine of the phase angle between voltage and current. When they are perfectly in step, the phase angle is 0 degrees, and cos(0) equals 1. So the power factor is 1, meaning all the power delivered is real power with no reactive component—this happens with a purely resistive load. If the phase angle were, for example, 90 degrees, the power factor would be 0 (all reactive power); if it were 180 degrees, the power factor would be -1 (current reversed relative to voltage). A phase shift like 60 degrees would give a power factor of 0.5.

Power factor is the cosine of the phase angle between voltage and current. When they are perfectly in step, the phase angle is 0 degrees, and cos(0) equals 1. So the power factor is 1, meaning all the power delivered is real power with no reactive component—this happens with a purely resistive load.

If the phase angle were, for example, 90 degrees, the power factor would be 0 (all reactive power); if it were 180 degrees, the power factor would be -1 (current reversed relative to voltage). A phase shift like 60 degrees would give a power factor of 0.5.