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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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The utility company that provides electrical energy to your home will typically charge you on the basis of the amount of electrical energy that are consumed. The unit kilowatt-hour is a unit of energy. Success on this question will involve three steps. First, calculate the energy (in units of watt-hour) used by the light bulb during its 8 hours of use. See the equation in the Formula Frenzy section. Second, convert the energy used in watt-hour to units of kilowatt-hour. There are 1000 watt-hour per kilowatt-hour. Third, use the cost per kilowatt-hour to determine the cost in cents. This third step of the question is as easy as determining the cost of buying 13 pieces of candy at 10 cents per piece. You can do it!
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