Cool Your School – What’s a Kilowatt-hour Good For?
What’s a Kilowatt-hour Good For?
Introduction
Given 1 kW-h of energy, what can an electrical appliance do? How long will a lamp shine before it’s
consumed 1 kW-h? How many slices of toast can a toaster make? How many loads of wash can a
washing machine get done?
As with many things, getting the answers to this requires a little math—so let’s play a little math energy
game.
Setup
Print out and cut up enough appliance cards (see end of this game packet) so that there are 5 cards per
student in the class. Randomly divide the cards into one envelope for each student, 5 cards in each.
Pass them out to your students when you are ready for them to play the game.
What To Do
Each appliance card represents a typical electrical appliance that might be found in a home or school.
The power rating, in Watts, is shown for each appliance.
Each appliance card also lists a “goal.” This is the “work” that you want to accomplish using the
appliance given a certain amount of energy to run it. This goal might be hours of running time, number
of pots of coffee made, or loads of laundry dried, for example.
For each appliance card, you will apply 1 kiloWatt-hour of energy to accomplish the listed goal. Use the
worksheet on the next page to do the calculation and record your results.
When the students are ready to play, tell them they have a certain amount of time to play the game and
calculate all of the card goals. The amount of time will depend on the math-readiness of the class, but
should be short enough to put a little bit of pressure on them….
When they’re ready, start the clock.
Discussion
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Cool Your School – What’s a Kilowatt-hour Good For?
Energy Worksheet
For each Appliance Card, determine the total amount of work the appliance can accomplish with 1
kiloWatt-hour of energy. See example calculations below.
Appliance
Power (W)
Power (kW)
Goal
Solution
Examples:
To determine how many hours an appliance will run on 1 kW-h of energy, use the formula
Time = Energy / Power, with Energy equal to 1 kW-h. So, given 1 kW-h of energy, a 500 W appliance will
run for:
1 kW-h / 0.500 kW = 2 hours
To figure out how many times an appliance can do its task on 1 kW-h (make toast, wash a load of
laundry, make a milkshake), first use the formula Energy = Power x Time to calculate how many kW-h it
consumes to do the task, then divide 1 kW-h by that amount.
So for a 500 W appliance that takes 15 minutes to do its task once, the energy it consumes is:
0.500 kW x 0.25 h = 0.125 kW-h
And dividing 1 kW-h by that amount:
1 kW-h / 0.125 kW-h = 8
This appliance can do its task 8 times on 1 kW-h of energy.
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Cool Your School – What’s a Kilowatt-hour Good For?
LED Night Light
Clock Radio
LED Lamp
0.5 W
4W
7W
Goal: DAYS of
continuous use
Goal: DAYS of
continuous use
Goal: HOURS of
continuous use
Incandescent Lamp
CFL Lamp
Desktop Computer
and LCD Monitor
60 W
18 W
290 W
Goal: HOURS of
continuous use
Goal: HOURS of
continuous use
Laptop Computer
Refrigerator
42” LCD TV
45 W
100 W
160 W
Goal: HOURS of
continuous use
Goal: DAYS of
continuous use
Goal: HOURS of
continuous use
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Goal: HOURS of
continuous use
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Cool Your School – What’s a Kilowatt-hour Good For?
Dishwasher (no
electric heating or
drying)
Air Conditioner
(small)
Toaster
750 W
500 W
200 W
Goal: HOURS of
continuous use
Goal: PIECES OF
TOAST (assuming 2
minutes to toast 2
slices)
Coffee Maker
Electric Heater
Electric Oven
900 W
1400 W
2000 W (at 350o F)
Goal: POTS OF
COFFEE (assuming 5
minutes to make 1
pot)
Goal: HOURS of
continuous operation
Goal: NUMBER OF
roasted turkeys
(assuming 2 hours to
cook a turkey)
Electric Clothes Drier
42” Plasma TV
XBOX
4400 W
330 W
70 W
Goal: NUMBER of
laundry loads
(assuming 45 minutes
to dry one load)
Goal: HOURS of
continuous operation
Goal: HOURS of
continuous
excitement
Goal: NUMBER OF
LOADS (assuming 45
minutes per load)
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Cool Your School – What’s a Kilowatt-hour Good For?
Classroom Lighting
Aquarium (10 gallon)
Ceiling Fan
600 W
30 W
50 W
Goal: HOURS of
continuous lighting
Goal: HOURS of
continuous use
(pump, heater, and
lighting included)
Goal: HOURS of
continuous use
Electric Blanket
Blow Drier
Waffle Iron
200 W
1000 W
1200 W
Goal: NIGHTS of use
(assuming 8 hours per
night)
Goal: Number of
times drying hair
(assuming 3 minutes
per drying)
Goal: Waffle
breakfasts (assuming
20 minutes to cook
one breakfast)
Electric Iron
Microwave Oven
Blender
1000 W
1000 W
300 W
Goal: Pieces of
clothing ironed
(assuming 2 minutes
per piece)
Goal: NUMBER of
meals cooked
(assuming 15 minutes
to heat a meal)
Goal: NUMBER of
milkshakes (assuming
1 minute per
milkshake)
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Cool Your School – What’s a Kilowatt-hour Good For?
Solution Key
Appliance
42" LCD TV
42" plasma TV
Air conditioner
Aquarium (10 gallon)
Blender
Blow drier
Ceiling fan
CFL lamp
Classroom lighting
Clock radio
Coffee maker
Desktop computer and LCD monitor
Dishwasher (no heating/drying)
Electric blanket
Electric clothes drier
Electric heater
Electric iron
Electric oven
Incandescent lamp
Laptop computer
LED lamp
LED night light
Microwave oven
Refrigerator
Toaster
Waffle iron
Xbox
W
160
330
500
30
300
1000
50
18
600
4
900
290
200
200
4400
1400
1000
2000
60
45
7
0.5
1000
100
750
1200
70
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kW
Goal Solution
0.16
6.25 Hours
0.33
3.03 Hours
0.5
2.00 Hours
0.03 33.33 Hours
0.3 200.00 Milkshakes (1 minute per)
1 20.00 Dry heads (3 minutes per)
0.05 20.00 Hours
0.018 55.56 Hours
0.6
1.67 Hours
0.004 10.42 Days
0.9 13.33 Pots (1 per 5 minutes)
0.29
3.45 Hours
0.2
6.67 Loads (45 min)
0.2
0.63 Nights (8 hours per night)
4.4
0.30 Loads of laundry (45 min)
1.4
0.71 Hours
1 30.00 Pressed clothing (2 minutes per piece)
2
0.25 Roast turkeys (2 hours per)
0.06 16.67 Hours
0.045 22.22 Hours
0.007 142.86 Hours
0.0005 83.33 Days
1
4.00 Meals (15 minutes per)
0.1
0.42 Days
0.75 80.00 Toast (2 per 2 minutes)
1.2
2.50 Waffle breakfasts (20 minutes per)
0.07 14.29 Hours
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