USCG Exam PracticeHand/power tools, measuring instruments, and maintenance
A wattmeter reads true power in an AC circuit directly because its deflection is proportional to which of the following?
- A. The product of voltage and current only, without regard to phase angle
- ✓ The product of voltage, current, and the cosine of the phase angleCorrect
- C. The square of the current multiplied by the circuit resistance
- D. The frequency of the supply voltage multiplied by the apparent power
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, something a simple volt-times-amp calculation cannot do. (NEETS Mod. 3 §1-4)
Cited:NEETS Mod. 3 §1-4