Lesson 9 Energy Efficiency
Energy Efficiency
No process can be 100% efficient—why?
C9.2 outdoor heat lamp
The meaning behind the second law of thermodynamics is that it is not possible to build a perfect machine—a machine that is 100% efficient. During any process, some energy is always converted into a form that is not useful to the end goal of the process.
The first law of thermodynamics says that energy changes forms. But with every change, waste energy is produced.
The energy that performs the task that the process set out to accomplish is called useful energy.
The energy that is not useful to the end process is said to be waste energy.
The energy that performs the task that the process set out to accomplish is called useful energy.
The energy that is not useful to the end process is said to be waste energy.
If machines and engines are to have moving parts to produce mechanical energy, the moving parts rub against one another and produce friction. Friction produces heat. In most machines, heat from friction causes issues and is unwanted.
The initial energy source in a system is called energy input.
The desired energy needed to do the work is called useful energy output.
In any device that involves energy conversions, how many conversions are in a device is related to the efficiency of the device. The more conversions there are, the less efficient the device will be. Why?
With every energy conversion, the amount of useful energy output is less than the energy input. As discussed in Lesson 8, a food chain is a good illustration of this. With every level in the food chain, less useful energy is available for the next organism. In fact, with just 10% of the useful energy being transferred to the next level, a food chain is one of the least efficient natural systems.
The initial energy source in a system is called energy input.
The desired energy needed to do the work is called useful energy output.
In any device that involves energy conversions, how many conversions are in a device is related to the efficiency of the device. The more conversions there are, the less efficient the device will be. Why?
With every energy conversion, the amount of useful energy output is less than the energy input. As discussed in Lesson 8, a food chain is a good illustration of this. With every level in the food chain, less useful energy is available for the next organism. In fact, with just 10% of the useful energy being transferred to the next level, a food chain is one of the least efficient natural systems.
Virtual Activity
Household Energy Usage © Explore Learning
Work through this activity to compare the energy used by different types of light bulbs found in a typical household. You will determine which is most efficient by considering how much light it produces in relation to its wattage.
Traditional light bulbs are incandescent lamps. In this bulb, an electric current passes through a thin tungsten filament. The filament heats up and glows, giving off light.
In a halogen lamp, the filament is encased in a glass capsule containing pressurized gas. This allows the filament to be heated to higher temperatures and emit brighter light.
In a fluorescent lamp, an electrical current passes through a gas inside a phosphor-coated tube. The gas emits ultraviolet radiation, which causes the phosphor to glow.
Please note: if you scroll down while in the Gizmo you will see a list of questions. You DO NOT need to complete these questions. You are able to complete them for extra practice if you would like.
Procedure
| Activity: Comparing Light Bulbs |
Get the Gizmo ready:
|
©Explore Learning
C9.3 image from lab of bedroom |
Which kind of light bulb uses the least amount of energy?
- Click on the play icon to open the Gizmo. You can also access the Gizmo by visiting the Online Resources for Print Students section of your online course.
- Form a hypothesis: Which of the three types of lamps do you think is the most efficient?
Click on the gather data tab to continue.Hypotheses will vary. For example: I think that the halogen lamp will be the most efficient. - Gather data: On the "BEDROOM" tab, click on the incandescent light to the right of the laptop computer on the desk, and the halogen lamp at the head of the bed. Record the wattage of each. Then select the "KITCHEN" tab
and record the wattage of the overhead
fluorescent lamp.
Note: A Watt is a measurement of the amount of energy used for every second the device is used. 1 Watt (W) = 1 Joule/second (J/s)
Incandescent lamp:
Halogen lamp:60 watts
Fluorescent lamp:300 watts
Click on the summarize tab to continue.30 watts - Summarize:
When the lamps are used for equal amounts of time, which one uses the most energy?
Halogen lamp
- Analyze: To gauge the efficiency of a light bulb, it is also important to consider how much light it produces. Light intensity is measured in lumens (lm). A lumen is equal to the light produced by a single candle.
The lumens produced by each type of light are listed below.
To compare the efficiency of each bulb, calculate how many lumens each bulb produces per watt. To do this, divide the number of lumens by the wattage for each lamp. Include all units.
Sample Calculation: «math» «mi»Lumens«/mi» «mo»§#160;«/mo» «mi»per«/mi» «mo»§#160;«/mo» «mi»watt«/mi» «mo»=«/mo» «mfrac» «mi»lumens«/mi» «mi»wattage«/mi» «/mfrac» «mspace linebreak=¨newline¨»«/mspace» «mi»Lumens«/mi» «mo»§#160;«/mo» «mi»per«/mi» «mo»§#160;«/mo» «msub» «mi»watt«/mi» «mrow» «mi»incandescent«/mi» «mo»§#160;«/mo» «mo»§#160;«/mo» «mi»bulb«/mi» «/mrow» «/msub» «mo»=«/mo» «mfrac» «mrow» «mn»800«/mn» «mo»§#160;«/mo» «mi»lm«/mi» «/mrow» «mrow» «mn»60«/mn» «mo»§#160;«/mo» «mi mathvariant=¨normal¨»W«/mi» «/mrow» «/mfrac» «mo»=«/mo» «mn»13«/mn» «mo».«/mo» «mn»33«/mn» «mo»§#160;«/mo» «mi»lm«/mi» «mo»/«/mo» «mi mathvariant=¨normal¨»W«/mi» «/math»
Lamp Lumens (lm)
Wattage (W)
Lumens per Watt
(lm/W)
incandescent 800 lm
halogen 6 000 lm
fluorescent 2 000 lm
Lamp Lumens (lm)
Wattage (W)
Lumens per Watt
(lm/W)
incandescent 800 lm
60 W
13.33 lm/W
halogen 6 000 lm
300 W
20 lm/W
fluorescent 2 000 lm
30 W
66.67 lm/W
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Which lamp produces light most efficiently?
The fluorescent lamp is the most efficient.
- The fluorescent lamp is the most efficient.
The incandescent lamp is least efficient.
When the lamps are used for equal amounts of time, which one uses the least energy?
Click on the analyze tab to continue.
Fluorescent lamp
Digging Deeper
©Wikicommons CC0
C9.4 EnerGuide label
C9.4 EnerGuide label
The EnerGuide label is the label you’ll find attached to most appliances. It tells you how much energy an appliance uses and makes it easier to compare the energy use of similar models of the same type of appliance.
The more energy efficient an appliance is, the less it costs to run and the lower your utility bills might be.
To learn more about EnerGuide labels, click on this link. https://www.nrcan.gc.ca/energy-efficiency/energuide-canada/energuide-label/13609
Learn More
Read This
Please read page 215 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on what useful energy and efficiency of a device or system are. Remember, if you have any questions, or do not understand
something, ask your teacher!
Practice Questions
Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice questions in your notes. After you have checked your answers, make corrections to your responses
(where necessary) to study from.
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Suppose you wanted to compare the efficiency of riding your bicycle compared to riding your skateboard. What would you measure as the energy input and what you measure as the useful energy output?
Your answer should be a variation of the following.
Energy input:the amount of chemical energy that you body used to provide the energy for you to ride the bicycle or skateboard
Useful energy output: the amount of kinetic energy that the bicycle or skateboard has once in motion