Journeyman Electrician Exam (NEC)General Electrical Knowledge and Plan ReadingMedium
A circuit has a total resistance of 25 Ω and is connected to a 120 V AC source. What is the total power dissipated by the circuit?
- A57.6 W
- B576 W
- C1440 W
- D4.8 W
Show answer & explanationAnswer & explanation
Correct answer: B. 576 W
To find the total power dissipated, use the formula P = V² / R, where P is power, V is voltage, and R is resistance. P = (120 V)² / 25 Ω = 14400 / 25 = 576 W.
Why the other options are wrong
- A. This might come from an incorrect formula or calculation (e.g., I*R).
- C. This would be V*R (120V * 25Ω), which is not a valid power formula.
- D. This would be the current (I = V/R = 120V/25Ω = 4.8A), not power.
Power Dissipation
Power dissipation refers to the rate at which electrical energy is converted into heat or other forms of energy within a circuit component.
- P = V² / R (Power = Voltage squared / Resistance)
- P = I² × R (Power = Current squared × Resistance)
- P = V × I (Power = Voltage × Current)
- Measured in Watts (W).
Memory trick: P = V I R² - Power is V-I-R-squared, like VIRUS but with R².