In a DC circuit with a 120 V source connected to a 40 Ω resistor, calculate the current and the power dissipated by the resistor.

• A. 2 A, 240 W
• B. 4 A, 480 W
• C. 1.5 A, 180 W
• D. 3 A, 360 W

Answer: (D)

Ohm's Law and the power relationships for a resistor connect voltage, current, and resistance. The current is found by dividing the voltage by the resistance: 120 V / 40 Ω = 3 A. The power dissipated is the product of voltage and current: P = V × I = 120 V × 3 A = 360 W. You can verify with P = I^2R = (3 A)^2 × 40 Ω = 360 W or P = V^2 / R = 120^2 / 40 = 360 W.