Calculate the electricity used in a typical household and learn about watts, kilowatts and kilowatt-hours.
Using practical examples of the appliances and objects found in every home, your students perform basic calculations to reveal how much electricity they use.
The watt (W) is a unit of electrical power, which is the rate at which an appliance or device uses energy.
A kilowatt (kW) is equal to 1,000 watts.
Energy is the ability to do work. Electrical energy use is measured in kilowatt-hours (kWh). Another unit of energy is the joule. For example, in homes we measure the use of natural gas energy in gigajoules.
A gigajoule (GJ) is equal to 1,000,000,000 (one billion) joules.
1 GJ equals 277.8 kWh.
You can either collect and assess the “Measuring electricity use” worksheet or have the class work through the answers together.
Worksheet answer key:
|Energy||The ability to do work||energy = power x time|
|Watt||A unit of electrical power. The rate at which an appliance or device uses power||1 watt = 1 joule/second|
|Power||The rate at which energy is transformed or the rate at which work is done||power = energy/time|
|Kilowatt||A measure of the amount of energy used over time that indicates how fast you are using energy||1 kW = 1,000 watts|
|Kilowatt-hour||The amount of energy used when an appliance or device consumes 1 kilowatt of power for 1 hour||100-watt light bulb x 10 hours of use = 1 kWh|
|Appliances and products||Power (watts)||Average use (hours per day)||Annual energy usage (kWh)||Annual cost ($ per year)|
|Vacuum cleaner||1,100||0.1||40.2 kWh||$3.33|
|Hair dryer||1,200||0.25||109.5 kWh||$9.08|
|Clothes dryer||4,000||2.0||2,920 kWh||$242.07|
|Incandescent light bulb||60||3.0||65.7 kWh||$5.45|
|Compact fluorescent light bulb||14||3.0||15.33 kWh||$1.27|
|LED light bulb||8||3.0||8.76 kWh||$0.73|
|Flat-screen TV||200||5.0||365 kWh||$30.26|
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