Which expression correctly represents power when using current and resistance as P = I^2 × R?

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

Answer: (C)

Power is the rate at which electrical energy is transferred or dissipated. In a resistor, that power can be expressed directly using the current through it and its resistance: P = I^2 R. This comes from starting with the general power formula P = VI and applying Ohm’s law V = IR. Substituting V with IR gives P = I(IR) = I^2 R, showing how the current and resistance alone determine the power dissipated as heat.

This form is especially useful when you know how much current is flowing and the resistance value. Other expressions involve voltage (P = VI or P = V^2/R); they’re related but require either the voltage or a different set of knowns. For example, P = I × R would yield a quantity with the units of voltage, not power, so it doesn’t represent power by itself.