2Electrical DevicesElectrical devices in the home are grouped into 4 different categoriesLight-producing (i.e. lamps & flashlights)Heat-producing (i.e. hair dryers)Mechanical (i.e. vacuum cleaners & drills)Audio-visual (i.e. TV & computers)
3Measuring Electricity A unit of energy is called a joule (J)A watt (W) is a unit used to measure electrical power
4Measuring Electricity If a device uses energy at the rate of one joule per second, then it’s power rating is one watt (W)Thus, energy can be measured in either joules (J) or watt seconds (W∙s)
5Measuring Electricity To measure the electrical energy consumed in the household (W∙s) is too small a unitHousehold electrical energy is commonly measured in the kilowatt hour (kW∙h)
6Measuring Electricity Example : One kilowatt equal 1000W, andone hour equals 3600s1 kW∙h = 1000W∙3600s1000 kW∙h x 3600s = W∙s
7Calculating CostSuppose your local electric company charges 7¢ per kilowatt hour of electricity. If your TV consumes (uses) at a rate of 200 watts, and the TV is on for 150 hours on average a month, how much would the monthly cost of power for the television be?
8Calculating Cost First, change the watts into kilowatts. 200 W = 0.2 kW Divide by 1000Next, multiply the number of kilowatts by the number of hours the TV runs.0.2 kW x 150 h = 30 kWhLast, multiply the number of kilowatt hours by the cost per kilowatt hour.30 kWh x $0.07/ kWh = $ 2.10Monthly cost for TV power
9Homework On one day, a household used a dryer for 2 hours, a colour TV for 4 hours, a vacuum cleaner for 1hour, and a toaster for 0.2 hours.a) What was the total energy these appliances consumed that day?b) If electrical energy costs 7¢/(kWh), what was the total cost of the energy used by these appliances on that day?