A 10 Ω resistor carries 2 A. What is the power dissipated, and what is the voltage across it?

• A. P = 20 W; V = 10 V
• B. P = 200 W; V = 20 V
• C. P = 40 W; V = 20 V
• D. P = 4 W; V = 2 V

Answer: (C)

Power in a resistor comes from the current through it and the resistance, via P = I^2R and V = IR. With a current of 2 A and a resistance of 10 Ω, the voltage across the resistor is V = I R = 2 × 10 = 20 V. The power dissipated is P = I^2 R = (2)^2 × 10 = 4 × 10 = 40 W. This also matches P = V I = 20 × 2 = 40 W, confirming consistency. So the resistor dissipates 40 W and has 20 V across it.