Which equation correctly expresses the power dissipated in a resistor when current and resistance are known?

• A. P = V^2 / R
• B. P = VI
• C. P = I^2 R
• D. P = R / I

Answer: (C)

Power dissipated in a resistor is the rate at which electrical energy becomes heat. When you know the current through the resistor and its resistance, the most direct way to find that power is P = I^2 R. This comes from combining Ohm’s law with the power formula: V = IR and P = VI. Substituting V with IR in P = VI gives P = I(IR) = I^2 R. That same relationship can also be seen by starting from P = V^2 / R and using V = IR, which yields P = (IR)^2 / R = I^2 R. Since the question provides current and resistance, using P = I^2 R uses the given quantities directly and avoids extra steps. The other forms require knowing voltage or are rearrangements, but they ultimately agree with this result once you apply V = IR.