Measuring Kilowatts

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SWBAT examine personal use of energy as measured in kilowatts by creating a spreadsheet to easily analyze data.

Big Idea

How much energy do we really use? Authentic technology integration is supported in the lesson as students create an Excel spreadsheet to analyze data. Students analyze the spreadsheet to determine a personal contribution to climate change.


15 minutes

To begin, my strategy it to promote an understanding of science vocabulary. I ask questions about electrical energy to determine my student's background knowledge of the words watt and kilowatt. I begin with a light bulb.

"Does anyone know how the electricity in this lightbulb is measured?"

I have a couple of students respond with watt or kilowatt. I ask for a definition. Typically students have heard of the words but cannot give definitions.  I project the definitions on the white board, students write the definitions in their notebooks and we add the words to the word wall.

My next strategy is an Exploration of Kilowatts to help students understand electrical energy used in common household products. I project a data table on the board for students to copy because I want to encourage learning organization. The column headings are Device, Watt, Kilowatt/hr, and hours.

I use Kill A-Watt devices and demonstrate how the device is used. This is usually fun. I plug a light bulb into the wall, a student reads it and we record the watts. I ask students to convert the light bulb watts into kilowatts. I do the same with the can opener. I ask students to predict how much time a lamp is used daily. We record the hours on the data table.

I do the same demonstration with the can opener. I get a chorus of, "What is that? An electric can opener?" I explain that there are some items that are used frequently and others used infrequently. With the little use of the can opener, I want to integrate math.  I suggest the can opener is used about 3 hours in a year. We discuss the math needed to convert 3 hours in a year to a daily number. By dividing by 365, we get .008 hours per day. I explain that there will be devices in which they will have to determine the hours down to the hundredth place. I get groans but once they get the hang of it, the student demand for precision kicks in and they easily use the calculations to gather data.   

An important part of this lesson is to plug an electronic device into the Kill-A-Watt machine without starting it. The students look at the Kill-a-Watt and see a number projected. I explain that electricity is being drawn from the plug even though the electronic device is not on. Students are amazed. I ask, "How many of you have something plugged into the wall that you rarely use?" Almost everyone says they do. I explain how some things are not practical to unplug like lamps, TVs, etc. I say, "What about your phone chargers? Hair dryers? Curling irons?" Many students admit they leave things plugged in that can easily be unplugged. 

Practice 1 Asking Questions and Defining Problems to identify and/or clarify evidence.


20 minutes

Before class I prepared for the lesson.  I have collected hair dryers, fans, cell phones, computers, laptops, and kitchen supplies: electric beaters, a toaster, a toaster oven, etc. I have three Kill-A-Watt stations and I place four or five devices at each station. Students move from station to station in groups, measuring the watts of the devices.

My next strategy is a comparison. I want to help students think about their prediction verses the truth. I ask the question,  “How much electricity do you think you use?” The students have no idea. I explain, if your light bulb uses .76 kilowatts about how much is that in an hour, a day, a month, and a year. They really have no idea and I like that they make ridiculous predictions. (At the end of the activity, I ask the same question after students have measured and examined kilowatt energy.) 

My next strategy is Small Group Investigations. I want to give the children hands-on experience measuring energy. Student groups move to Kill-A-Watt stations and test various devices. The investigation includes converting from watt to kilowatt to encourage students to reason quantitatively.  

Students use Rapid Tables Energy Consumption Calculator for the devices not available in the classroom. Check out Kilowatt Student Samples to see examples of student data tables. 

Math Practice 2: Reason quantitatively

Science Practice 3:  Planning and Carrying Out Investigations

Conduct an investigation to produce data to serve as the basis for evidence that meet the goals of the investigation. Evaluate the accuracy of various methods for collecting data.Collect data to produce data to serve as the basis for evidence to answer scientific questions. Collect data about the performance of a proposed tool under a range of conditions. 


40 minutes

I integrate technology in a strategy that allows students to work independently. Before the lesson I use screenshot video to create instructional videos with step-by-step instructions. These videos teach students how to use Microsoft Excel. In partner groups, students go to the computer. I like partners because inputting data can be tedious and students make careless mistakes. With two people, the opportunity for checking work is better.  

Students create a spreadsheet with the following column headings: Device, Watts, Kilowatts, Monthly, Yearly. My instructional videos teach students how to create a spreadsheet, input data, and use formulas to easily calculate yearly kilowatt usage.  

Practice 5 Using Mathematics and Computational Thinking Use digital tools to analyze very large data sets for patterns and trends. Use mathematical representations to describe and/or support scientific conclusions and design solutions. Create algorithms (a series of ordered steps) to solve a problem. 


5 minutes

Students have completed the data table so now it is easy to analyze data. The data collected is purposefully incorrect.  I want students to consider the limitations of data analysis. I ask, "Do you think this is a true reflection of your family's energy use? Why or why not?" I love this strategy because the students know they use electricity more than we can record in class.  You will see in my Data Limitations movie that many students explain the data is true of their electricity use. Because of this I use a Group Share strategy so students can discuss the limitations.

Students answer the following reflection questions.

  1. Look at your predicted kilowatt measurement from the beginning of the lesson. How was your final measurement different? Why were the numbers so different? My strategy is to connect to student emotions, hoping students will be surprised by the amount of electricity they use. The students who put in a lot of thought are sometimes close. Others are wildly off. 
  2. Are the numbers  a true reflection of your use of energy?  
  3. What can be done to give you a more precise picture of the energy you use?
  4. How did the spreadsheet help you analyze the data? My strategy is to reflect upon how technology helps analyze large amounts of data. 

It is eye-opening to students as they realize how the kilowatts are still not a clear reflection of their electricity use.  By considering the limitations of their data, students can  explain how to improve the accuracy of the data they collected.

Next I ask students to consider the question, "What did you learn about your family's electricity use?"  I couple the question with the strategy, Write to Learn. Students write a three to five sentence summary describing their family's  kilowatt use. They are required to use their kilowatts data to answer the question. My intention is to make a personal connection to energy use. I ask, "What could you do to use less electricity? Why would you want to use less electricity?"

Many time students have a difficult time starting summaries. I use sentence starters to support my students as they write summaries. I offer the following sentence starters:

  • "I learned..." 
  • "My family's energy..."
  • "I impact climate change....."  My students have recently been taught Exploring Climate Change and they have background knowledge about the causes of climate change.

Practice 4 Analyzing and Interpreting Data: Analyze and interpret data to provide evidence for phenomena. 

Practice 6 Constructing Explanations and Designing Solutions: Construct an explanation using models or representations. 


40 minutes

A parent built me a bike on a roller bar attached to a motor. This useful device gives my students the ability to “feel” energy. I place an incandescent light bulb in the socket and ask a student to pedal. Then I change it out to a CFL bulb. There is a noticeable difference between the physical energy needed to power each of the bulbs. 

Check out my lesson Use a Generator to Light It Up! for a more thorough explanation of physically testing energy output.