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**12. 2 Using Electrical Energy Wisely. (Pages 492- 500)**

12.2 Using Electrical Energy Wisely (Pages ) Key Concepts: (Page 500)

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The electrical power of an appliance is the rate at which it uses electrical energy. The practical unit for electrical power is the kilowatt (kW). The electrical energy that is used by an appliance at a given setting is calculated by multiplying its power rating (in kW) by the amount of time that it is used (in hours, h). The practical unit of electrical energy is the kilowatt-hour (kW.h).

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Smart meters allow a utility company to charge different amount for each kW.h of energy that is used at different times of the day. The electricity that is consumed by an appliance or device when it is turned off is called the phantom load.

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**Efficiency = useful energy output/ total energy input**

The efficiency of an electric device is the ratio of useful energy output to total energy input: Efficiency = useful energy output/ total energy input

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Power Ratings One factor that affects the amount of electrical energy used in your home is the power ratings of your appliances and devices. 2. The actual power rating of any particular appliance appears on a EnerGuide label on the outer casing of the appliance. 3. The electrical energy of an appliance is its rate of use of electrical energy. 4. Electrical power is measured in watts, although the practical unit for most appliances is the kilo watt hour (kW-h).

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Appliance Settings: 5. A second factor that affects the amount of electrical energy used by appliances and devices is their settings. 6. The actual power used by an appliance or device maybe different from the power rating. 7. What is the typical power rating of the following appliances? Clock kW DVD player kW Microwave oven 1.5 kW Toaster 1.1 kW Video game console 0.10 kW

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**Calculating Cost of Energy:**

The cost of electrical energy depends on the amount of energy that is used and the price that is paid for it. This cost is calculated by multiplying the electrical energy in (kWh) by the price per (kW/h). Electrical energy (E) = Power (P) x time used (t) Cost (C) = E x price

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