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Graphic on Meter ReadingProblem:
Every time you turn on a television, stereo, light, or hair dryer, you use electrical energy. Did you know that Iowa depends upon coal for over 85% of its electric generation within the state? You can estimate how much electrical energy you and your classmates use while watching television. Then you can estimate how much coal power plants must burn to make that much electricity.
Procedure:
The amount of electrical power -- or the number of watts -- that a television and other common electrical appliances use is shown in the table. Multiply the number of watts by the average number of hours you watch television each day. The number of watt-hours is the amount of electrical energy you use. Now, estimate the total number of watt-hours the students in your classroom use each day by watching television.
Watt-hours = power x time
Appliances and Average Power Ratings
Color Television: 200 watts
VCR: 150 watts
Hair Dryer: 1000 watts
Use Your Math:
1. Electric power plants need about 1 kilogram of coal to produce around two thousand watt-hours of electrical energy. How much coal do the students in your classroom use each day just by watching television?
2. How many kilograms of coal would the students in your classroom use in a year if they continue watching television as much as they do now?
3. About 80 million homes in the United States have at least one television. Suppose these families watch television as much as you do. How many kilograms of coal would be used to watch television in the United States each day? Each year?
Challenge: How much coal is required to keep a 100 watt light bulb burning 24 hours a day for one year?
Teacher Notes
Objective:
The student will develop an awareness of the amount of electrical power they use by calculating the amount of coal needed to generate power for some common electrical appliances.
NOTE TO THE TEACHER: You can use this activity in one of several ways. You can give the students a copy of the student sheet and let them attempt the calculations on their own, or you could help them with the first math problem. Another approach would have the teacher present the background for the students and not hand out the student sheet.
Background:
Every time you turn on a television, stereo, light, or hair dryer, you use electrical energy. Iowa depends upon coal for over 85% of its electric generation. You can estimate how much electrical energy your students use while watching television. Then, you can estimate how much coal power plants must burn to make that much electricity.
The average amount of electrical power -- or the number of watts -- that a television uses is 200 watts. Multiply this number of watts by the average number of hours a student watches television each day. The number of watt-hours is the amount of electrical energy used. Have each student calculate their watt-hours used watching television in an average day.
If the appliance wattage is not given, use amp rating and voltage to find watts.
P = amps x voltage
Watt-hours = P x time
Materials:
1 kilogram of coal (2.2 lbs)
calculators
overhead transparency with USE YOUR MATH 1, 2, and 3 written out for the students to see.
Teaching Suggestions:
1. "Use Your Math" #1 should be presented as a large group activity to acquaint students with the procedure used to calculate the amount of coal used.
2. Students may then proceed to "Use Your Math" #2 and #3 and the challenge question on their own or in cooperative groups.
3. Use the coal to show students how much 1 kilogram of coal is.
Use Your Math Activities:
1. Electric power plants need about 1 kilogram of coal to produce about two thousand watt-hours of electrical energy. How much coal do the students in your classroom use each day just by watching television?
2. About how much coal would the students in your classroom use in a year if they continue watching television as much as they do now?
3. About 80 million homes in the United States have at least one television. Suppose these families watch television as much as you do. Approximately how much coal would be used to watch television in the United States each day? Each year?
Extended Activities:
1. Select another appliance students have in their homes. Students can read the power rating and calculate as they did in Activities 1 and 2 to find the number of kilograms of coal used per day/month/year.
THE TEACHER MUST STRESS TO THE STUDENTS THE IMPORTANCE OF HAVING AN ADULT PRESENT WHENEVER THEY ARE INVESTIGATING AN APPLIANCE FOR WATTAGE.
2. Check the power rating (watts) on different models/makes of the same appliance.
Average power ratings of other electrical appliances
Water heater (regular recovery) -- 2500 watts
Refrigerator/freezer -- 600 watts
(frost free 17 cubic ft.)
Microwave oven -- 1475 watts
Clothes dryer (electric) -- 6000 watts
Coffee maker -- 800 watts
Crockpot -- 240 watts
Toaster oven -- 1500 watts
Problem:
How do you read your electric meter?
Your electric meter has an important job to do. The meter measures how much electrical energy the many lights and electrical appliances in your home consume. Every time you turn on an electric appliance electricity moves through the electric meter. When people pay electric bills they are paying for the electricity used in their homes. Electric companies measure electric energy in a unit called a kilowatt-hour. A kilowatt-hour equals using 1000 watts continuously for one hour. Leaving a 100 watt light bulb on for 10 hours would use 1 kilowatt-hour of electricity. You can learn how to read your meter so that you can keep track of how much electrical energy you and your family use each day.
An electric meter may have four or five dials. The dials are like the face of a watch, but only use the numbers 0 to 9. Every other dial reads backwards. Look at the illustrations of meter dials on the next page. Study the dials and the readings. When you understand how to make the readings, write instructions on how to read an electric meter. Make sure the instructions are clear enough for another person to understand.
To find out how much energy you used during a given period of time (say one day or one week) you must compare readings made at the beginning and end of the period. For example, suppose your meter reads 13478 on Monday morning and 13488 on Tuesday morning:
13488 (Tuesday)
-13478 (Monday)
10 Kilowatt-hours (Kwh)
This means that your home consumed 10 Kwh's during the 24-hour period from Monday morning to Tuesday morning.
Use Your Math:
Use the meter dial hand-out to keep track of the electric energy used in your home for four days. Have an adult assist you in locating the meter at your home. Remember to read the meter at the same time each day. You can figure out the cost of electricity you used for the four days. Multiply the kilowatt-hours used by the amount of money the electric company in your community charges for each kilowatt-hour. (Some meters are digital -- they just show the numbers)
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Graphic on Meter Reading
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Graphic on Meter Reading
Teacher Notes
Objectives:
1. The student will read a four or five-dial electric meter.
2. The student will determine kilowatt hours of electricity consumed.
3. The student will calculate the amount of electricity consumed in student homes during one week.
Background:
Electric meters measure the amount of electric energy used in kilowatt hours (Kwh). A typical electric meter has four or five dials. You read the dials from right to left and record the readings in the same order. Each dial is numbered from 0 to 9. Usually, the pointer on a dial will be between two numbers. In this case, always read the lower of the two numbers. Notice some dials move clockwise and some counterclockwise. In cases where the pointer is directly on a number -- say 8, you have to check the dial immediately to the right. If the pointer on that dial has passed '0,' record the higher number '8' shown on the first dial. If the pointer has not passed '0' record the lower number '7'.
Materials:
Dials made from oak tag, magic markers, construction paper, and brass paper fasteners.
Student sheets "How Do You Read Your Electric Meter?," and "Reading An Electric Meter," and "How Much Electricity Do We Use?"
Teaching Suggestions:
1. Read and discuss paragraphs one and two from "How Do You Read Your Electric Meter?" Practice using the oak tag visuals (students may make these in cooperative groups) and the top three examples of student handout.
2. Read and discuss paragraph three. Complete the activity. Read and discuss paragraphs four and five (Part B). Pass out Student Activity. Sheet C, entitled "How Much Electricity Do We Use?" Record meter readings for Monday and Friday. Some meters have digital read outs. In this case instruct students to just record the numbers that show.
Extended Activity:
Have students list several ways they can reduce energy use in their homes. Students can take another reading, implement the ideas, and determine the amount of energy saved for a five day period.
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