# Electric Circuits - Mission EC6 Detailed Help A light bulb is plugged into a 120-Volt outlet and left on for 10 minutes. If it uses up 90000.0 Joules of energy, then what is the power rating (in Watts) of the light bulb? (Note: The numbers in this problem are randomly selected and may differ from those above.) Mathematically, power is a rate quantity - a time-based quantity. It is the rate at which an appliance transforms electrical energy into other forms of energy. The power (P in Watts) of a light bulb is related to the energy transformed by the bulb (∆E in Joules) and the time (t in seconds) that the bulb is used. These quantities are related by the equation P = ∆E / t. The standard metric unit of time is seconds. Substitution of time into the equation in the Formula Frenzy section must be done in units of seconds. It would be a wise idea to first convert the time in minutes to units of seconds. Then perform the substitution into the equation. An introductory Physics course will typically include a lot of algebraic problem-solving. Students quickly gain an impression that every numerical value provided within a problem must be used. But don't be fooled! Physics should involve an understanding of physical concepts and not simply plug-and-chug exercises. In Physics, we attempt to answer questions about the physical world. In answering such questions, we must discriminate between information that is pertinent and information that is impertinent to the solution. The ability to make decisions about the pertinence of such information comes from a solid grasp of concepts and definitions. In this problem, such discrimination allows a student to recognize that the voltage is not important to the solution of the problem.  