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 which quantity?
- A. The product of voltage and current only, without regard to phase angle
- ✓ The product of voltage, current, and the cosine of the phase angle between themCorrect
- C. The square of the current multiplied by the circuit resistance
- D. The ratio of real power to reactive power as indicated by the power-factor meter
Why B is correct
NEETS Mod. 3 §1-4 states that the wattmeter's deflection is proportional to the product of voltage, current, and the cosine of the phase angle, so it reads true power in watts directly and automatically accounts for power factor. A simple volt-times-amp product gives only apparent power.
Cited:NEETS Mod. 3 §1-4