CSLB C-10 Electrical ContractorElectrical Theory and CalculationsMedium
A technician observes that a single-phase motor operating on a 240V supply draws 15 amps with a power factor of 0.8. What is the approximate real power consumed by the motor?
- A3.6 kW
- B4.5 kW
- C28.8 kW
- D2.88 kW
Show answer & explanationAnswer & explanation
Correct answer: D. 2.88 kW
Real power (P) for a single-phase AC circuit is calculated as P = V * I * Power Factor. P = 240V * 15A * 0.8 = 2880 watts or 2.88 kW.
Why the other options are wrong
- A. This would be the apparent power (V*I), not real power, and possibly a conversion error.
- B. This value is too high, possibly from an incorrect power factor or calculation error.
- C. This is 10 times the correct answer, indicating a misplaced decimal or unit conversion error.
Single-Phase Real Power
Real power (P) in a single-phase AC circuit is the actual power consumed by the load that performs useful work, calculated as the product of voltage, current, and the power factor.
- Formula: P = V * I * Power Factor.
- Measured in watts (W) or kilowatts (kW).
- Power factor (PF) ranges from 0 to 1, representing efficiency of power use.
- Real power is also known as active power or true power.
Memory trick: Real power works, Reactive power wastes, Apparent is the sum of fates.