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Here is the problem: A current of 3 A flows through a 12 Ω resistor. What is the voltage across it?

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Use the Ohm prime s law formula, rearranged for the unknown, in SI units.

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Formula: Ohm prime s law.

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Substitute the known values.

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Power dissipated.

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So the answer is voltage V equals 36 V; P equals 108 W.

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Ohm prime s law says the current through a resistor is proportional to the voltage across it: V equals IR. It holds for ohmic conductors such as resistors at constant temperature, not for diodes or filament bulbs over wide ranges.

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Substituted every value back into the formula: both sides agree, which checks out.