Plugged In To CO2

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Students analyze the energy consumption of a household appliance and estimate the amount of carbon dioxide it is adding to the atmosphere each year.

Learning Objectives

  • Students will use a meter to measure the energy use of appliances and electronics, record and analyze the data.
  • Students will learn that different appliances and electronics use different amounts of energy.
  • Students will learn that energy is generated in a variety of ways, primarily with fossil fuels which contribute greenhouse gases such as CO2 to the atmosphere.
  • Students will calculate the amount of CO2 emitted by use of an appliance over a year.


  • Kill-a-Watt meter
  • Power strip and outlet
  • A collection of small appliances and lamps (may include toaster, microwave, hairdryer, lamp with CFL, lamp with incandescent bulb, phone and charger, laptop and charger, TV, video game player, blender, nightlight, vacuum, coffee maker, fan)
  • Pencils
  • Optional extension: chart paper, marker, sticky notes

Materials to print


  • Copy student sheets for each student
  • Copy Fuel Types in U.S. Regions for each pair of students or prepare to project it via LCD or overhead.


  1. Introduce units used in energy science: A watt is a unit of power. 1000 watts is called a kilowatt. On many appliances and light bulbs, the wattage is listed. Watt-hours and kilowatt-hours (1000 watt-hours) are used to describe how much power is used over an amount of time.
  2. Provide an example to foster student understanding of energy units: A 60 watt incandescent light bulb pulls 60 watts of electricity out of an outlet when it is on. If that light is on for an hour, it has used 60 watt-hours. If you forget and leave the light on next to your bed all day from 6:00 am until midnight (18 hours) it would have used (60 x 18) 1080 watt-hours of electricity. That's 1.080 kilowatt-hours (kWh) of electricity.
  3. Give an overview of this activity: Not all electronics use the same amount of electricity. Some need more watts to operate than others. In Part 1 of this activity, you will investigate how much electricity different lights, technology, and appliances need. In Part 2, you will calculate the amount of carbon dioxide that is produced by using this electricity. (Introduce the role of greenhouse gas emissions in climate change if it has not been a part of students' prior learning.)

Part 1

  1. Set up the appliances, electronics, power strip, and Kill-a-Watt meter at the front of the room
  2. Introduce students to the Kill-a-Watt meter. The meter allows us to assess how much electricity an appliance is consuming. It plugs into an outlet and then the appliance plugs into it. It measures the flow of electricity coming from the outlet to the appliance in watts.
  3. Select two appliances and ask students to guess which uses more electricity.
  4. Have a student measure both appliances with the Kill-a-Watt meter and share results with the class. Have students record the data in the first and second columns of the table on Student Sheet 1. (Note that the watts measured on the meter may not completely stabilize at one value. Help the student making the measurement to choose a reasonable number.)
  5. Take one of the two appliances and ask students to choose another from the collection. Ask students to guess which uses more electricity.
  6. Have another student measure the new appliances with the Kill-a-Watt meter and share results with the class. Have students record the data in the table on Student Sheet  1 (1st and second columns).
  7. Continue this process until all appliances and electronics have been tested. There is space on the student sheet for nine appliances, but you may decide to test more or less with your students.
  8. As a class, estimate how long each appliance is used each day. Fill in that information in Student Sheet  1 (3rd column).
  9. Calculate how many kWh per day and per year each appliance uses. (If time is limited, consider having pairs of students work on this calculation for a single appliance and then sharing data.)
    1. Multiply watts by hours per day to get watt-hours (4th column).
    2. Divide watt-hours by 1000 to get kWh per day (5th column).
    3. Multiply kWh per day times 365 to get kWh per year (6th column).

Part 2

  1. Tell students that in this part of the activity they will figure out how much carbon dioxide is produced with the use of each appliance. Carbon dioxide, a greenhouse gas is emitted into the atmosphere when fossil fuels are burned. The release of carbon dioxide and other greenhouse gases into the atmosphere is the primary cause of recent global warming. In the United States, most of our electricity is produced by burning fossil fuels like coal and gas.
  2. Introduce students to the data on the page, Fuel Types in U.S. Regions. This data, from the US EIA, shows the mix of energy sources found in different parts of the country. Find your region's on the map, and then its row in the table. Discuss as a class how your region's energy sources are similar to, or different from, other parts of the country. Instruct students to complete steps 1 and 2 on Student Sheet 2.
  3. Have students work in pairs or small groups, focused on an appliance or electronic device from Part 1 (step 3 on Student Sheet 2)
  4. Have each pair/group calculate how many kWh per year of electricity used by their appliance come from each energy source. These values should be recorded in column 2 of the table.The general calculation is:

[kWh] x [% of energy converted to decimal] = kWh from fuel source.

  1. Tell students that the amount of carbon dioxide released to generate electricity depends on how much comes from fossil fuels. Use your kWh calculations from the previous step with the information in column 3 of the table on Student Sheet 2 to calculate the amount of CO2 released by each fossil fuel. The general calculation is:

[kWh from fuel source] x [Lb of CO2 per kWh] = Lb of CO2 produced

  1. Students should add the three amounts of CO2 together to get the total pounds of CO2 sent into the atmosphere by using the appliance or electronic device over a year.
  2. Have student groups share their results with the rest of the class.


Discuss as a class:

  • Did the devices that use the most energy (according to the kill-a-watt meter) also produce the most carbon dioxide? Why or why not? (Students should recognize that both the amount of watts used by an appliance and the length of time that it is used impact its total energy use and emissions.)

  • How can we reduce the amount of carbon dioxide emitted to the atmosphere while still using these devices? (One solution is to use the devices less often. Another solution is to switch energy sources to use renewable energy, which doesn’t emit carbon dioxide.)

Optional Extension: Create a Driving Question Board as a Starting Point for Project-based Learning 

  1. Once students have connected how one or more devices generates carbon dioxide emissions, you may wish to have them expand their understanding and investigate how to decrease the greenhouse gases produced by their school’s energy use. If time allows, this can become a project-based learning activity. 

  2. Use a Driving Question Board (DQB) to help students define what they want to learn about their school energy use and greenhouse gas emissions. The DQB is a tool to document questions and can serve as a way to help students focus their questions and define what they will investigate as a project. 

  3. To make the DQB, write the main question (“How can we decrease carbon dioxide emissions from electricity use in our school?”) on a sheet of chart paper. If students will be working on projects related to the questions, plan to keep the DQB posted in the classroom as students work on projects. 

  4. Introduce the DQB and its main question and have students write questions related to the main question on sticky notes and post them on the chart paper. 

  5. Once all questions have been added to the DQB, have students form groups of related questions. These groups of questions will be the basis of student projects. Questions will vary and may include:

    • How much energy does the school uses and how much carbon dioxide emissions does it create?

    • What's the local mix of energy sources (more specific than the regional mix that students used to calculate emissions earlier in this activity)?

    • Would it be possible to switch to some or all renewable energy?

    • Is there a way for the school to use less energy?

  6. Refer to project-based learning resources such as PBLworks and Boston University's Project-Based Learning Guide for more information about how to support student learning and ensure well-designed projects.


Anything with a plug (appliances, electronics, lamps) draws power through an electrical outlet. Many of these items are left on all day and night. Other items draw some electricity even when they are turned off (called a “phantom load”). In Part 1 of this activity, a device called a Kill-a-Watt meter is used to measure the power consumption of appliances and other devices. The meter gives instantaneous measures of volts (voltage) and amps (a measure of current) as well as the watts of power being used (Note: watts= volts x amps). The meter also gives a measure of the amount of power used over time in kWh if you leave the device in place for a length of time (from just a couple of minutes to weeks or even months). See the Consumer Reports Test of Energy Monitors (March 2009) for more information. Kill-a-Watt meters sell for $20-$25. They are also available at some public libraries.

Electricity is generated in different ways in different regions depending, in part, on local natural resources. The pie charts on the map used in Part 2 of this activity show how the mix of electricity sources varies with region of the United States. On average, within the United States, about half of electricity is generated using coal. Natural gas and nuclear power account for about 20% each. Nearly 10% of electricity is from renewable sources, with the bulk of that produced at hydroelectric dams. Petroleum makes a very small fraction of US electricity. Coal, natural gas, and petroleum are fossil fuels. Burning these fuels emits carbon dioxide and other greenhouse gases to the atmosphere, as well as other air pollutants such as sulfur dioxide and volatile organic compounds (VOCs). Electricity generation produces about 40% of the greenhouses gases emitted in the United States. Other nations have different energy mixes. If you are not from the US, contact your country's department of energy for information on the energy mix.

Carbon dioxide (CO2) and other greenhouse gases trap infrared energy emitted from the Earth’s surface and warm the atmosphere. This is a natural process that is being amplified by the additional greenhouse gases added to the atmosphere mainly through the burning of fossil fuels. These additional gases are causing the greenhouse effect to grow stronger, causing global warming. Prior to the Industrial Revolution, carbon dioxide in our atmosphere was at approximately 280 ppm (parts per million). As of 2009, carbon dioxide in our atmosphere is approximately 386 ppm and growing steadily upward.


Investigate phantom loads. Is it plugged in when not in use? Does that use electricity? Test the appliances and electronics when turned off to see which use electricity.

Do an energy audit for your school using Kill-a-Watt meters to measure energy use for copiers, computer labs, and other devices that plugin and then calculating energy use from lights, heating, and other electronics and appliances that do not have plugs.

Do the CO2 How Much Do You Spew activity, which allows students to get a larger perspective on individual energy use.