How do you calculate electrical power in a DC circuit?

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

Answer: (D)

Power is the rate at which electrical energy is delivered or consumed. In a DC circuit, the universal way to calculate it is by multiplying the voltage across an element by the current through it: P = V × I. This definition comes from how voltage drives current and how that flow does work on the circuit component.

If the component follows Ohm’s law (V = IR), you can rewrite the same power in other useful forms: P = I²R or P = V²/R. These are helpful in special cases—P = I²R applies when you know current and resistance, and P = V²/R applies when you know voltage and resistance.

The other expressions aren’t generally correct for power. P = I × R would give a quantity with voltage units, not watts. P = V − I isn’t a meaningful way to compute power in a circuit context.