Master Electrician Exam (NEC)General Electrical KnowledgeMedium
A master electrician is troubleshooting a 120V AC circuit that has an inductive load. A voltmeter measures 120V and an ammeter measures 10A. A wattmeter, however, indicates only 960W. What is the power factor of this circuit?
- A0.8
- B0.6
- C0.9
- D0.7
Show answer & explanationAnswer & explanation
Correct answer: A. 0.8
Power factor is calculated as the ratio of true power (measured by the wattmeter) to apparent power (Volt-Amperes). True Power = 960W, Apparent Power = 120V * 10A = 1200VA. Power Factor = 960W / 1200VA = 0.8.
Why the other options are wrong
- B. This would indicate a lower true power or higher apparent power.
- C. This would indicate a higher true power or lower apparent power.
- D. This would indicate a lower true power or higher apparent power.
Power Factor (AC Circuits)
Power factor is the ratio of true power (P, measured in Watts) to apparent power (S, measured in Volt-Amperes) in an AC circuit. It indicates how effectively electrical power is being converted into useful work.
- Calculated as P/S or cos(θ) where θ is the phase angle.
- Ranges from 0 to 1; 1 is ideal (purely resistive).
- Low power factor indicates reactive power (inductive/capacitive).
Memory trick: Power Factor: Real Power Over Apparent Power, It's The Truth!