Unit D Lesson 14: Reducing Energy Loss and Increasing Efficiency
Completion requirements
Unit D Lesson 14: Reducing Energy Loss and Increasing Efficiency
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Learning Targets |
Big Question: How can we prevent
energy
loss and increase
efficiency?
We each need to take steps to ensure we are not wasting electricity.
We each need to take steps to ensure we are not wasting electricity.
At the end of this inquiry, you should be able to answer the following questions:
- What is the law of the conservation of energy?
- How do I determine the electrical efficiency of a device?
- How do I compare the efficiency of various devices?
Pages 335 to 342 in your textbook will help you answer these questions.
Introduction
Using Energy Creates Many Concerns
Is it better to hang our clothes out to dry or to use an electric or gas dryer? Should you wash dishes by hand or in the dishwasher? How warm is your house at night? Our day-to-day activities involve using energy 24 hours a day. Even when we are sleeping, our furnaces are still going, clocks are ticking, and fridges are running. Why give attention to energy use? How does our energy use affect our world?
Is it better to hang our clothes out to dry or to use an electric or gas dryer? Should you wash dishes by hand or in the dishwasher? How warm is your house at night? Our day-to-day activities involve using energy 24 hours a day. Even when we are sleeping, our furnaces are still going, clocks are ticking, and fridges are running. Why give attention to energy use? How does our energy use affect our world?
Skill Builder
The Use of Energy Always Involves Loss of Energy
Recall from Section 1 the law of conservation of energy. Energy cannot be created or destroyed; it only changes form. However, energy use in devices shows that output energy is always lower than input energy. Where does the missing energy go? The perfect device with 100% efficiency does not exist. During energy changes, there is always a portion of energy lost in forms that we don't desire. For example, a gasoline-powered vehicle changes chemical energy to mechanical motion, but some energy is always lost as heat and sound. We calculate efficiency to help us realize the amount of energy we are losing and to try to find ways to minimize the waste.
Efficiency is expressed in a mathematical equation
Recall from Section 1 the law of conservation of energy. Energy cannot be created or destroyed; it only changes form. However, energy use in devices shows that output energy is always lower than input energy. Where does the missing energy go? The perfect device with 100% efficiency does not exist. During energy changes, there is always a portion of energy lost in forms that we don't desire. For example, a gasoline-powered vehicle changes chemical energy to mechanical motion, but some energy is always lost as heat and sound. We calculate efficiency to help us realize the amount of energy we are losing and to try to find ways to minimize the waste.
Efficiency is expressed in a mathematical equation
(useful energy output / total energy input ) x 100% = % efficiency
Sample calculation for calculating efficiencies
A. Write what you know.
B. Select and chose formula.
C. Substitute into formula.
D. Write answer in a sentence.
Find the efficiency of a 22 watt fluorescent bulb that produces 66240 J of
energy over a 4.0-hour period.
A. Write what you know/
B. Select and chose formula.P = 22 W
t = 4.0 h
Energy output = 66240 J
First, we must calculate the energy available to the system, which we call energy input.
C. Substitute into formula.E = P x t
E = P x t
E = (22W)(4.0 hours x 60 min x 60 sec)
= 316 800 J
D. Write answer in a sentence.Now that we know the output and input energy, we can put them into the efficiency formula.
(Energy output/ Energy input) x 100 = % Efficiency
(66240/316800) x 100 = 21%
The fluorescent bulb is 21% efficient.
Practice β Calculating Efficiency
Read the question and answer each question in the same format as the examples.
Read the question and answer each question in the same format as the examples.
A. Write what you know.
B. Select and chose formula.
C. Substitute into formula.
D. Write answer in a sentence.
Question 1
A 1100 W electric kettle takes 7.0 minutes to boil some water. If it uses 196 000 J of energy to heat the water, what is the efficiency of the kettle?
A 1100 W electric kettle takes 7.0 minutes to boil some water. If it uses 196 000 J of energy to heat the water, what is the efficiency of the kettle?
A. Write what you know.
B. Select and chose formula.P = 1100 W
t= 7.0 min x 60 sec = 420 seconds
E input = ? J
E output = 196 000 J
C. Substitute into formula.E= P x t
E = (1 100 W)(420 s)
E = 462 000 J
D. Write answer in a sentence.(Energy output/ Energy input) x 100 = % Efficient
(196 000 J/462 000 J) x 100 = 42% efficient
The kettleβs efficiency is 42%.
Question 2
A gasoline-electric hybrid vehicle has an energy input of 675 000 Joules and a useful energy output of 195 000 J. What is the efficiency of the vehicle?
A gasoline-electric hybrid vehicle has an energy input of 675 000 Joules and a useful energy output of 195 000 J. What is the efficiency of the vehicle?
A. Write what you know.
B. Select and chose formula.Energy input = 675 000J
Energy output = 195 000 J
C. Substitute in formula.(Energy output/Energy input) x 100 = % Efficient
D. Write answer in a sentence.(195 000J/675000J) x 100 = 29%
The vehicle is 29% efficient.
Energy Output and Input
If you are having trouble deciding which is the energy output and which is the energy input, here is a hint: the smaller number always goes on the top. This is because the amount of energy input is ALWAYS greater than the energy output, and the amount of energy in is considered to be 100%. No use of energy is 100% efficient, so the smaller number has to be the energy output.
If you are having trouble deciding which is the energy output and which is the energy input, here is a hint: the smaller number always goes on the top. This is because the amount of energy input is ALWAYS greater than the energy output, and the amount of energy in is considered to be 100%. No use of energy is 100% efficient, so the smaller number has to be the energy output.
Figure 1 β Many newer electric appliances come with "eco" settings that use less energy and increase efficiency.
Watch
To see how to calculate efficiency, watch "Efficiency Calculation".
For an in-depth look at calculating efficiency, view "Calculating Electrical Efficiency" and "How to Calculate Efficiency Problems".
Are All Light Bulbs Created Equal?
A good example for showing efficiency in everyday life is by comparing an incandescent light bulb to halogen, florescent, and LED light bulbs.
A good example for showing efficiency in everyday life is by comparing an incandescent light bulb to halogen, florescent, and LED light bulbs.
Incandescent light bulbs are only 5% efficient, which means that 95% of the energy these light bulbs use is lost to heat. The incandescent light bulb is a very wasteful device and, as a result, is being phased out of use in Canada. Stores have a large variety of alternative types of light bulbs such as those referred to as halogen and florescent.
Halogen lights are a better alternative to light bulbs, but they are only 15% efficient, which means they lose significant amounts of energy to heat as well. Not only is this inefficient, but the heat produced can cause fires. Halogen bulbs last 2 to 6 times longer than regular incandescent light bulbs.
Fluorescent tubes pass a current through mercury gas that causes the white tubes to glow. Fluorescent tubes are about 20% efficient and last 10 to 13 times longer than incandescent bulbs do, but they still lose a lot of energy.
LEDs β those using light emitting diodes β are the latest in household light bulbs. Think of an LED as a bundle of tiny diodes the size of specks of pepper, each emitting light with very little heat. Currently, they are expensive,
but they last up to 25 times longer than incandescent, and they use only 25% of the energy that incandescent bulbs use to produce the same amount of light. They change very little electrical energy to heat. LEDs operate for about half the cost of
CFLs (Compact Fluorescents) and about one-tenth the cost of incandescent β based on the cost of producing 800 lumens (the output of the familiar 60-watt incandescent). LEDs operate for about half the cost of CFLs (Compact Fluorescents) and about one-tenth
the cost of incandescent β based on the cost of producing 800 lumens (the output of the familiar 60-watt incandescent).
Energy Efficiency is Important for our Planet
Earth does not have unlimited amounts of fossil fuels to help generate electricity. Scientists continue to search for innovative ways to generate electricity and improve the efficiency of devices. We can eliminate energy waste by being conscious of our everyday behaviours. Instead of drying the clothes in an electric dryer, we can air-dry them. We can turn down our household thermostats to reduce the heat at night or when we leave home. Can you think of other ways we can eliminate energy waste? A good place to start would be to read page 342 in your textbook.
Earth does not have unlimited amounts of fossil fuels to help generate electricity. Scientists continue to search for innovative ways to generate electricity and improve the efficiency of devices. We can eliminate energy waste by being conscious of our everyday behaviours. Instead of drying the clothes in an electric dryer, we can air-dry them. We can turn down our household thermostats to reduce the heat at night or when we leave home. Can you think of other ways we can eliminate energy waste? A good place to start would be to read page 342 in your textbook.
Interactive
Conserving Energy
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The BrainPOP video, reviews the concept of energy conservation.
Click here
to watch "Conserving Energy".
You will need a username and password to access the video.
- Username: 0099
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Password: students
-
Click here
to complete the quiz on Conserving Energy. Remember to check your answers at the end!