Power is defined as

• A. The rate at which work is done.
• B. The energy stored in a capacitor.
• C. The voltage across a component.
• D. The current times resistance.

Answer: (A)

Power is the rate at which work is done or energy is transferred. It tells you how quickly energy flows into or out of a system. In mechanics, P = W/t, and since W = F·d and velocity v = d/t, you can also write P = F·v. In electrical contexts, power is the rate of energy transfer and can be written as P = I·V. For a resistor, power can also be expressed as P = I^2 R or P = V^2 / R. The idea described as the rate at which work is done matches power. The energy stored in a capacitor is an amount of energy, not a rate; the voltage across a component is a potential difference, not a rate; and I·R equals voltage by Ohm's law, not power by itself (though power can be written as I^2 R or V^2 / R).