Which formula expresses electrical power in a circuit?

Which formula expresses electrical power in a circuit?

• A. P = V × I
• B. P = I × R
• C. P = V ÷ I
• D. P = R × I

Answer: (A)

Power in an electrical circuit is the rate at which energy is transferred, and it is found by multiplying the voltage across a component by the current through it. So the correct formula is power equals voltage times current, P = V × I. This makes sense because volts times amperes gives watts, the standard unit of power. You can see why the other expressions aren’t power: dividing voltage by current yields resistance (Ohm’s law), and multiplying current by resistance gives voltage, not power. (If you want, you can also express power using Ohm’s law as P = I²R or P = V²/R, but the fundamental relationship is P = VI.)

Power in an electrical circuit is the rate at which energy is transferred, and it is found by multiplying the voltage across a component by the current through it. So the correct formula is power equals voltage times current, P = V × I. This makes sense because volts times amperes gives watts, the standard unit of power.

You can see why the other expressions aren’t power: dividing voltage by current yields resistance (Ohm’s law), and multiplying current by resistance gives voltage, not power. (If you want, you can also express power using Ohm’s law as P = I²R or P = V²/R, but the fundamental relationship is P = VI.)