USCG Exam PracticeHand/power tools, measuring instruments, and maintenance
A wattmeter reads true power in an AC circuit rather than apparent power because its deflection is proportional to:
- A. Voltage multiplied by current only, without regard to phase angle
- ✓ The product of voltage, current, and the cosine of the phase angleCorrect
- C. The insulation resistance measured between the current coil and the voltage coil
- D. Frequency deviation from the nominal 60 Hz bus frequency
Why B is correct
The wattmeter's deflection is proportional to the product of voltage, current, and the cosine of the phase angle, which is the definition of true power. This automatically accounts for power factor, which a simple volt-times-amp calculation cannot do. (NEETS Mod. 3 §1-4)
Cited:NEETS Mod. 3 §1-4