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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.
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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.
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