Power dissipated by a 12V source across a 4-ohm resistor?

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Multiple Choice

Power dissipated by a 12V source across a 4-ohm resistor?

Power in a resistor comes from how much voltage is across it and its resistance, described by P = V^2 / R (or P = VI or P = I^2R). With 12 V across a 4 Ω resistor, the current is I = V/R = 12/4 = 3 A. Then P = VI = 12 × 3 = 36 W. This also matches P = I^2R = (3)^2 × 4 = 9 × 4 = 36 W, or P = V^2 / R = 12^2 / 4 = 144 / 4 = 36 W. So the power dissipated is 36 watts.

Power in a resistor comes from how much voltage is across it and its resistance, described by P = V^2 / R (or P = VI or P = I^2R). With 12 V across a 4 Ω resistor, the current is I = V/R = 12/4 = 3 A. Then P = VI = 12 × 3 = 36 W. This also matches P = I^2R = (3)^2 × 4 = 9 × 4 = 36 W, or P = V^2 / R = 12^2 / 4 = 144 / 4 = 36 W. So the power dissipated is 36 watts.

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