Which equation correctly expresses electrical energy transferred by a device with constant power over time?

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Multiple Choice

Which equation correctly expresses electrical energy transferred by a device with constant power over time?

When power stays the same, the energy transferred over a period is found by multiplying the power by the time. Energy E = P t. This is because power is the rate at which energy is delivered, so with constant power you just scale that rate by how long it runs. For example, if P = 50 W and the device operates for t = 10 s, the energy transferred is E = 50 × 10 = 500 J. The other expressions describe instantaneous power (P = I^2 R, P = V I, P = V^2 / R); they don’t give energy by themselves unless you multiply by time. If you include time, you’d get E = I^2 R t, E = V I t, or E = V^2/R × t, which are energy values for a resistor over that time.

When power stays the same, the energy transferred over a period is found by multiplying the power by the time. Energy E = P t. This is because power is the rate at which energy is delivered, so with constant power you just scale that rate by how long it runs. For example, if P = 50 W and the device operates for t = 10 s, the energy transferred is E = 50 × 10 = 500 J. The other expressions describe instantaneous power (P = I^2 R, P = V I, P = V^2 / R); they don’t give energy by themselves unless you multiply by time. If you include time, you’d get E = I^2 R t, E = V I t, or E = V^2/R × t, which are energy values for a resistor over that time.

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