Power Ratings and Electric Cost

The total amount of energy an appliance uses is measured in units called watts. One watt of power is delivered when a current of one amp flows through a circuit of one volt. To measure large quantities of power, such as the electric power used in a home, the kilowatt is used. A kilowatt is equal to 1,000 watts.

All electric appliances have a power rating. The power rating of an electric appliance is the amount of energy used per unit of time. The most common way to rate power of appliances is the kilowatt-hour. A 100 watt light bulb, for example, will use 100 watts of electric power in one hour of usage. Therefore, a 100 watt light bulb will use 1/10th of a kilowatt in an hour. A 600 watt refrigerator will use 600 watts per hour, or .6 kilowatts per hour. A 1,500 watt hair dryer will use 1.5 kilowatts of power in one hour

The power company charges about 6.5 cents per kilowatt hour. Using this information, calculate the following:

1. How much does it cost to watch TV for one hour, if the TV has a power rating of 300 watts?


2. How much does it cost to run a dishwasher for 30 minutes, if the dishwasher has a power rating of 2,300 watts?


3. How much does it cost to operate an electric oven for 4 hours, if the oven has a power rating of 2,600 watts?

4. How much does it cost to operate a microwave oven for 15 minutes, if the power rating of the microwave is 1,000 watts?


5. How much does it cost to operate an electric clothes dryer for one and one half hours, if the power rating of the dryer is 4,000 watts?


6. How much does it cost to operate a radio with a power rating of 50 watts, for one year?


7. How much does it cost to operate an electric clock with a power rating of 3 watts for five years?


8. If your home used 1,500 kilowatts of power, what will LP&L charge for this power?


9. If your electric bill is $150 for a month of electric power, how many kilowatts of power did you use for that month?


10. Refrigerator A costs $1,000 and has a power rating of 500 watts. Refrigerator B costs $800 and has a power rating of 700 watts. Assuming continuous use, which refrigerator would be the most economical to buy and use for a five year period?


How much money would you save by buying and using this refrigerator rather than the other refrigerator?


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