CSLB C-10 Electrical ContractorElectrical Theory and CalculationsEasy
A 240V single-phase heating element draws 20 amps. What is the total power consumed by the element?
- A7.2 kW
- B9.6 kW
- C4.8 kW
- D2.4 kW
Show answer & explanationAnswer & explanation
Correct answer: C. 4.8 kW
For a resistive single-phase circuit, power (P) is calculated using the formula P = V * I. Multiply the voltage by the current to find the power in watts, then convert to kilowatts.
Why the other options are wrong
- A. This is a calculation error, possibly confusing it with three-phase power.
- B. This is a calculation error, likely multiplying by an incorrect factor.
- D. This is a calculation error, possibly using half the voltage or current.
Single-Phase Real Power (Resistive)
Real power in a single-phase resistive circuit is the actual power consumed by the load, converted into heat or useful work. It is measured in Watts (W).
- Calculated as P = V * I.
- For purely resistive loads, power factor is 1.
- Represents the power doing useful work.
Memory trick: Power is like a 'VIP' - Voltage x Current gives Watts.