In a pure resistor, what is the phase angle between voltage and current, and what is the power factor?

• A. φ = 0°, PF = 1
• B. φ = 90°, PF = 0
• C. φ = 0°, PF = 1
• D. φ = -90°, PF = 0

Answer: (C)

In a pure resistor, voltage and current rise and fall together with no delay between them. That means the phase angle between voltage and current is zero degrees. The power factor is the cosine of that angle, so PF = cos(0°) = 1. So voltage and current are in phase and the circuit has unity power factor. The other cases describe reactive elements where the phase shift is 90°, which would give a power factor of zero.