Power factor can only be

• A. PF equals 2
• B. PF is unbounded
• C. −1≤PF≤+1
• D. −1≥PF≤+1

Answer: (D)

Power factor is the cosine of the phase angle between voltage and current. Since the cosine of any angle always lies between -1 and +1, the power factor cannot exceed those bounds. The sign tells you whether the current leads or lags: a positive value means the current lags voltage (inductive, absorbing real power with reactive power drawn), while a negative value means the current leads voltage (capacitive, delivering reactive power back to the source). In most practical terms, the magnitude is between 0 and 1, but with sign it spans from -1 to +1. So the correct description is that power factor lies within -1 and +1 inclusive.