5.2 Energy Transformation Technologies. Section 5.1 Questions

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1 5.2 Section 5.1 Questions 1. If our oil reserves are dwindling at a rate of 6%/a, what percent of our current supply will remain after 24 a? 2. (a) What is the approximate current cost per litre of regular gasoline? (b) At an estimated average rate of increase of 4.5%/a, what is the doubling time of the cost of gasoline? (c) What will be the cost per litre of gasoline when you reach retirement age? (d) What factors make it almost impossible to judge what the rate will be in the future? 3. Between 1990 and 2000, the growth of the world s population was 1.5%/a, and in 2000, the population reached 6.0 billion people. (a) If this growth continues, when will the population reach 12 billion people? (b) Show that at this growth rate, after only 2100 years (which is less time than has elapsed since Aristotle lived), the total mass of all the people on Earth would exceed Earth s total mass. (c) Based on this example, explain why continuous growth is not always a good thing. Applying Inquiry Skills 4. Make up three or four pertinent survey questions that would help you judge how much the average citizen knows and cares ab the issue of energy supply and use in Canada. Making Connections 5. What is meant by a population growth rate of zero? Do you believe that all countries in the world should aim for this rate? Explain. 6. Energy is not only important in physics; it is significant in all walks of life. Follow the links for Nelson Physics 11, 5.1 to discover more. Describe how energy relates to each area of interest listed: industry, economics, technology, communication, travel, agriculture, leisure, medicine, politics, and scientific research. GO TO Energy Transformation Technologies Imagine if you had to pedal an exercise bike to create the electricity needed to operate the lights, computer, radio, TV, or any other electrical device you use. What a difference there is between the amount of pedalling you would have to do and the simple job of plugging the device into the electrical let! As you know, electrical energy is a very convenient form of energy. However, it never originates in such a convenient form. It must be transformed from some other form of energy before it is delivered to where it will be used. A system that converts energy from some source into a usable form is called an Using Energy in Our Society 165

2 energy transformation technology or energy converter: a system that converts energy from some source into a usable form Figure 1 The Maritime Electric Generating Station Borden converts the chemical potential energy in natural gas into electrical energy. DID YOU KNOW? Generating Electricity After several days with electricity and heat during the ice storm in Eastern Canada in 1998, an Ontario family pedalled a bicycle connected to their gas furnace in order to create the electricity needed to operate the furnace. One person in the family was an engineer who knew how to connect the cycle to the furnace safely. Table 1 Typical Efficiencies of Energy Transformation Technologies Device Efficiency (%) electric heater 100 electric generator 98 hydroelectric power plant 95 large electric motor 95 home gas furnace 85 wind generator 55 fossil fuel power plant 40 automobile engine 25 fluorescent light 20 incandescent light 5 energy transformation technology. (Another name for this type of system is an energy converter.) Energy transformation technologies are specific examples of energy transformations, presented in Chapter 4. An electrical generating station, such as the one shown in Figure 1, is an important example of an energy transformation technology. It converts energy, such as chemical potential energy stored in coal, oil, or natural gas, into electrical energy. It would be very inconvenient for you to try to generate electricity at your school by burning coal! Unfortunately, energy transformation technologies are not 100% efficient. According to the law of conservation of energy, the amount of energy present before an energy transformation is equal to the amount of energy present after. However, very often, some of the energy is not converted into a useful form and is wasted. As from Chapter 4, in efficiency = E 100% E Some transformations are more efficient than others, as shown in Table 1. Practice 1. Not many generations ago, homes, schoolhouses, and other buildings were heated by wood stoves or coal furnaces. Describe reasons why today s methods of providing heat are safer and more convenient. 2. Refer to the data in Table 1. (a) Both fossil-fuel power plants and hydroelectric power plants produce electrical energy. Why is one so much more efficient than the other? (b) Both incandescent lights and electric heaters produce heat. Why do they have such a big difference in efficiency? (c) Which of the two light-producing devices must operate at a higher temperature? How can you judge? Making Connections 3. Our society has come to rely heavily on energy transformation technologies, which we often take for granted. However, we soon realize how dependent we are on these technologies when there is an electrical black. Describe the effects that would occur in your area as a result of an electrical black that lasts from several hours to several days. Automobile Efficiency Cars, trucks, boats, airplanes, and other vehicles that burn fuel to operate are common energy transformation technologies. To learn ab the efficiency of these technologies, we will focus on the automobile. Automobiles are highly inefficient. Suppose that an amount of fuel containing 1000 J of chemical potential energy is used by an automobile s engine. Figure 2 shows what happens to this energy in a car with an internal combustion engine. The efficiency of the car is efficiency E 100% Ei n 100 J 100% J efficiency 10% 166 Chapter 5

3 J of energy in the fuel 750 J In the engine: fuel is vaporized and mixed with air the fuel-air mixture is drawn into the cylinder, which contains a piston a spark from the spark plug ignites the mixture, producing a high temperature and pressure pressure pushes on the piston, which turns the crankshaft, which turns the transmission waste heat is carried away by exhaust gases pushed through the cylinder's exhaust valve and by a water-antifreeze mixture circulating from the car's radiator 150 J 100 J In the transmission: energy is transferred through the differential to the wheels heat caused by friction is generated (and lost) in the transmission, differential, and wheels Useful energy: only 100 J of useful work is done in producing the kinetic energy of the moving car Figure 2 Heat loss in a typical car Engineers around the world are always seeking ways to reduce energy consumption. Making machines more efficient is one way of doing this. Practice 4. (a) Calculate the efficiency of the car engine described in Figure 2 up to the point where the energy reaches the transmission. (b) Why is the efficiency of the entire car, shown to be only 10%, less than the value you determined in (a)? 5. Assume that a fossil fuel power plant has an put of 2500 MW and an efficiency of 38%. (a) Determine its put energy in one day. (b) Calculate the input energy required to produce this put energy. Answers 4. (a) 25% 5. (a) J (b) J Lab Exercise Determining Waste Energy In Chapter 4, you studied the principle of heat exchange, efficiency, and power. You can combine these concepts to carry calculations of the results of a laboratory investigation to compare the efficiencies of different ways of transforming electrical energy into thermal energy. In this lab exercise, you will analyze a controlled experiment in which a 1.1-kg sample of pure water with an initial temperature of 12 C was heated until it reached a temperature of 58 C. The temperatures are measured by a thermometer supported in such a way that the bulb does not touch the. A stopwatch was used to determine the total time interval needed to cause this temperature change. The sample was slowly and constantly stirred during the Using Energy in Our Society 167

4 heating process. This procedure was repeated using other sources of heat, as summarized in Table 2 under Evidence. Prediction (a) By comparing the five setups shown in the illustration, predict which heat source and corresponding setup will waste the least amount of energy in heating the water. Rank the setups, from least to greatest energy wasted, according to your predictions. Evidence Table 2 shows the sources of heat and the observational data for the experiment. Table 2 Source Electric kettle Electric stove Hot plate Hot plate Hot plate Power (W) Setup beaker t (s) Analysis (b) Copy Table 2 into your notebook, and add the following rows: Output energy (J), Input energy (J), Waste energy (J), Efficiency (%). (c) Apply the Chapter 4 equations to determine the values needed to complete the Evidence table. (The specific heat capacity of water is J/(kg C).) (d) Describe patterns you observe in the calculations of energy wasted and efficiency. (e) Describe factors that influence the efficiency of the heat sources in this lab exercise. (In your answer, be sure to discuss where the wasted energy has gone.) (f) If you were to perform a similar experiment, what safety precautions would you implement? Evaluation (g) Evaluate your predictions in (a). (h) Describe sources of random error and systematic error in the experiment. (To review random and systematic errors, refer to Appendix A.) Synthesis (i) Assume you were testing an energy transformation technology to determine the efficiency with which it cooks noodles or potatoes. (i) What factors would you control? (ii) How do you think the efficiency would compare if you were to place a cover on the? Why? 168 Chapter 5

5 5.3 SUMMARY Energy Transformation Technologies An energy transformation technology converts energy from some source into a usable form; for example, a fossil-fuel generating station converts chemical potential energy into electrical energy. Almost all energy transformation technologies operate at efficiencies less than 100%. A lot of the wasted energy becomes thermal energy. The efficiency of an energy transformation technology can be found using the equation in efficiency E 100%. E Section 5.2 Questions 1. State whether each statement below is true or false, and justify your answer. (a) Energy transformation technologies are more important to individual Canadians now than they were when Canada first became a country. (b) Energy transformation technologies are more important on a daily basis to people living on the Caribbean Islands than to the average Canadian. 2. Write the energy transformation equation for an automobile. 3. An electric kettle, rated at 1.5 kw, heats 1.1 kg of water from 14 C to 99 C in 4 min 45 s. Determine the efficiency of this application of an energy transformation technology. 5.3 Energy Resources You have seen that energy transformation technologies convert energy from some source into a useful form of energy. The original source of the energy, called an energy resource, is a raw material obtained from nature that can be used to do work. A resource is considered renewable if it renews itself in the normal human lifespan. All other resources are considered non-renewable. Both types will be explored in this section. Figure 1 illustrates Canada s main sources of energy. Approximately 11% of Canada s energy consumption originates from water power (at waterfalls, for example). This resource is renewable. Almost all the remaining energy consumption comes from non-renewable resources crude oil, natural gas, and coal, which are fossil fuels, and uranium. Non-Renewable Energy Resources Fossil fuels make up the largest portion of non-renewable energy resources. Energy from fossil fuel begins as radiant energy from the Sun that is absorbed by plants. The plants use the energy to manufacture carbohydrates, which store energy. Most of the stored energy is used during the lifetime of the plants, but some remains after their death. If the plants are buried, they do not disappear; energy resource: raw material obtained from nature that can be used to do work renewable energy resource: an energy resource that renews itself in the normal human lifespan non-renewable energy resource: an energy resource that does not renew itself in the normal human lifespan nuclear power coal hydro power natural gas other Figure 1 Canada s sources of energy oil Using Energy in Our Society 169