Overview

Using practical examples of the appliances and objects found in every home, your students perform basic calculations to reveal how much electricity they use.

What you'll need

• "Measuring electricity use" worksheets for each student

Instructions

1. Introduce your students to the terms “watts” and “kilowatts”. These are units used when measuring electrical power.
   • A watt is the rate that an appliance or device uses energy: 1 watt = 1 joule/second
   • The higher the wattage, the more power the device or appliance uses
   • A kilowatt is 1,000 watts
2. Remind your class that energy is the ability to do work. Electricity is a source of power that can do work for us. To determine how much electrical energy an object uses we have to know two things:
   • The amount of electricity the object uses, called its power rating
   • For how long the object is using electricity.
   • To calculate the amount of work an object does, use the formula: energy = power x time
3. The amount of energy used over time uses the unit “kilowatt-hours,” which is 1,000 watts used in 1 hour. This is a rate of power: the rate at which work is done.
   • Ask 10 of your students to draw a light bulb and label it 20 W, then stand up with their drawings
   • Imagine that these ten 20 W bulbs are on (working) for five hours
   • How many kilowatt-hours have been used?
   • 10 bulbs x 20 W x 5 hours = 1,000 watt hours = 1 kWh
4. Have another 10 students draw 20 W bulbs, but vary the amount of time they are “working”.
5. Hand out the “Measuring electricity use” worksheet. As a class, come up with definitions for the following terms:
   • Energy
   • Watt
   • Power
   • Kilowatt
   • Kilowatt-hour
6. Have your students complete the worksheet individually or in pairs.