If a 9 V supply delivers 0.5 A to a load, what is the power in watts?

If a 9 V supply delivers 0.5 A to a load, what is the power in watts?

• A. 0.5 W
• B. 4.5 W
• C. 9 W
• D. 18 W

Answer: (B)

Power in a circuit is found by multiplying the voltage by the current. With 9 V and 0.5 A, the power is 9 × 0.5 = 4.5 watts. You can check this another way: the resistance is R = V/I = 9/0.5 = 18 ohms, and then P = I^2R = (0.5)^2 × 18 = 0.25 × 18 = 4.5 W (or P = V^2/R = 9^2/18 = 81/18 = 4.5 W). So the power is 4.5 watts. The other numbers would require different voltage or current values.

Power in a circuit is found by multiplying the voltage by the current. With 9 V and 0.5 A, the power is 9 × 0.5 = 4.5 watts. You can check this another way: the resistance is R = V/I = 9/0.5 = 18 ohms, and then P = I^2R = (0.5)^2 × 18 = 0.25 × 18 = 4.5 W (or P = V^2/R = 9^2/18 = 81/18 = 4.5 W). So the power is 4.5 watts. The other numbers would require different voltage or current values.