Kill-A-Watt Meter
Demonstration Guide
Objective: To help student understand more about energy use and how to calculate energy
(kilowatt-hour) from the Kill-A-Watt power meter.
Subjects: Scientific Method, Math, Earth Science, Language Arts, Computer Skills
Duration: 10-20 minutes in class to complete the demonstration
Materials: 1) A Kill-A-Watt Meter or other type of power meter and b) A lamp to be used with
two light bulbs; a) incandescent (75 watt) and b) CFL OR LED (15 watt). Other electric
appliances can also be measured.
Procedure: (Note that background info is provided at the end of this sheet)
A) Introduce the concept of measuring energy using the scientific method
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Question: Is there a difference in energy use between two different types of light
bulbs? An incandescent bulb (regular light bulb) and a compact fluorescent (CFL) or
LED light?
Hypothesis: Have students answer the question and state which light bulb they think
will use less energy.
Method Use the Kill-A-Watt meter to measure and quantify how much power (in
Watts) each light bulb will use.
Result: Perform the experiment by using the method and record the data. Now show
students how to calculate energy (kilowatt-hour) from the power meter (Watts).
Energy (kWh) = power (W)/1000 * time (hours)
Conclusion: Have students state whether or not their prediction or hypothesis was
correct
B) Kill-A-Watt Demo
(Remember to have familiarized yourself with the Kill-A-Watt meter to make on the fly
corrections when needed.)
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Plug your Kill-A-Watt meter into a wall outlet.
Plug the lamp into the Kill-A-Watt meter, put in a light bulb and turn it on.
Press the middle button to display Watts.
Read the power used by the light bulb in Watts (W). Repeat and compare with
the other light bulb or any electrical device.
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Convert watts (power) to energy (kilowatt-hours).
Calculate how much it costs to run each light bulb for an hour.
Background Information
1. What is a watt?
A watt is a measure of the instantaneous energy usage (power)
2. What is a kilowatt-hour?
This is a measure of energy, which is the amount of power used (Watts) over a given
amount of time (an hour)
3. Where does our power for electricity come from?
It depends, (trick question) in California the majority is derived from power plants fueled
by natural gas. Other parts of the country depend on burning coal to create power. It is
important for students to understand that power is created by different sources and when
fossil fuels such as natural gas and coal are burned they emit greenhouse gases. Wind and
solar are also used to produce energy, but they don’t emit greenhouse gases.
4. Why is it import to be energy efficient?
The less energy we consume, the less greenhouse gas emissions are released into the
atmosphere. Reducing energy also saves money.
5. How do I calculate how much energy a 100W light bulb uses in 8 hours? We
multiply the power (100W) by the time of use (8 hours) to get 100W x 8 hours= 800Wh.
Then convert from watt-hours to kilowatt-hours by dividing by 1000, so the answer is 0.8
kWh.
6. How much money does it cost to run a 100W light bulb for 8 hours? We first
calculate the energy used in 8 hours (as above) and then multiply by the cost of energy
per kWh. In California, a kWh of energy costs about $0.16. So, 0.8kWh of energy costs:
0.8kWh x $0.16/kWh = $0.128 (about 13 cents). For a home that leaves a 100W light
bulb on all year for 8 hours a day, the cost is $0.128*365=$46.72 a year!
Incandescent bulb
75W
7. used for 10 hours =750 Wh
75W
or 0.75 kWh (kilowatt-hours)
Cost = .75kWh x $0.16=$0.12
LED (or CFL) bulb
15W
15W used for 10 hours = 150 Wh
or 0.15 kWh (kilowatt-hours)
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Cost = .15kWh x $0.16=$0.02
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