FAA Aviation Mechanic General (AMG)Fundamentals of Electricity and ElectronicsHard
A technician tests an AC circuit and reads 100 volts on the voltmeter, 5 amps on the ammeter, and 300 watts on the wattmeter. What is the power factor of this circuit?
- A1.0
- B0.3
- C0.6
- D0.5
Show answer & explanationAnswer & explanation
Correct answer: C. 0.6
Apparent power equals voltage times current: 100V × 5A = 500 VA. Power factor equals true power divided by apparent power: 300W / 500VA = 0.6. This indicates the circuit has some reactive component causing voltage and current to be out of phase.
Why the other options are wrong
- A. A power factor of 1.0 would only occur in a purely resistive circuit with no phase difference.
- B. This value is too low and does not match the calculation of 300/500.
- D. This would only be correct if apparent power were 600 VA.
Power Factor (AC Circuits)
The ratio of true power (watts) to apparent power (volt-amps) in an AC circuit, indicating how effectively current is converted into useful work.
- Formula: PF = True Power / Apparent Power
- Apparent Power = Voltage x Current (VA)
- PF = 1.0 only in purely resistive circuits
Memory trick: True power is the 'useful work,' apparent power is the 'total effort' — PF shows efficiency.