Power factor is defined as cos φ, where φ is the phase angle between voltage and current. What is PF when φ = 0?

Power factor is defined as cos φ, where φ is the phase angle between voltage and current. What is PF when φ = 0?

• A. 1
• B. 0
• C. -1
• D. 0.5

Answer: (A)

Power factor is the ratio of real power to apparent power and is defined as cos φ, where φ is the phase angle between voltage and current. When φ is zero, voltage and current are in phase, so there is no reactive power and all the power is real. cos(0) equals 1, so the power factor is 1 (unity), meaning S = P. If the phase angle were 90 degrees, the power factor would be 0 (purely reactive); if it were 180 degrees, the power factor would be -1 (current opposite the voltage). A phase angle of about 60 degrees would give a power factor around 0.5.

Power factor is the ratio of real power to apparent power and is defined as cos φ, where φ is the phase angle between voltage and current. When φ is zero, voltage and current are in phase, so there is no reactive power and all the power is real. cos(0) equals 1, so the power factor is 1 (unity), meaning S = P. If the phase angle were 90 degrees, the power factor would be 0 (purely reactive); if it were 180 degrees, the power factor would be -1 (current opposite the voltage). A phase angle of about 60 degrees would give a power factor around 0.5.