Energy is defined as the ability to do work.

A.produces pressure

B.imparts energy to a fluid to move it from level ‘A’ to level ‘B’

C.creates a vacuum to move a liquid in all installation

D.is to develop a pressure differential

A.低能态跃迁到中等能态 Transition from low energy state to medium energy state

B.中等能态跃迁到高能态 Transition from medium energy state to high energy state

C.高能态跃迁到低能态 Transition from high energy state to low energy state

D.低能态跃迁到高能态 Transition from low energy state to high energy state

A.中等能态跃迁到高能态 Transition from medium energy state to high energy state

B.高能态跃迁到低能态 Transition from high energy state to low energy state

C.中等能态跃迁到低能态 Transition from medium energy state to low energy state

D.低能态跃迁到高能态 Transition from low energy state to high energy state

E.低能态跃迁到中等能态 Transition from low energy state to medium energy state

A.中等能态跃迁到高能态 Transition from medium energy state to high energy state

B.高能态跃迁到低能态 Transition from high energy state to low energy state

C.中等能态跃迁到低能态 Transition from medium energy state to low energy state

D.低能态跃迁到高能态 Transition from low energy state to high energy state

E.低能态跃迁到中等能态 Transition from low energy state to medium energy state

A.中等能态跃迁到高能态 Transition from medium energy state to high energy state

B.高能态跃迁到低能态 Transition from high energy state to low energy state

C.中等能态跃迁到低能态 Transition from medium energy state to low energy state

D.低能态跃迁到高能态 Transition from low energy state to high energy state

E.低能态跃迁到中等能态 Transition from low energy state to medium energy state

A.中等能态跃迁到高能态 Transition from medium energy state to high energy state

B.高能态跃迁到低能态 Transition from high energy state to low energy state

C.中等能态跃迁到低能态 Transition from medium energy state to low energy state

D.低能态跃迁到高能态 Transition from low energy state to high energy state

E.低能态跃迁到中等能态 Transition from low energy state to medium energy state

h that is converted to heat buildings and generate electricity. The idea of harnessing Earths internal heat is not new. As early as 1904, geothermal power was used in Italy. Today, Earths natural internal heat is being used to generate electricity in 21 countries, including Russia, Japan, New Zealand, Iceland, Mexico, Ethiopia, Guatemala, El Salvador, the Philippines, and the United States. Total worldwide production is appr0aching 9,000 MW (equivalent to nine large modern coalburning or nuclear power plants)—double the amount in 1980. Some 40 million people today receive their electricity from geothermal energy at a cost competitive with that of other energy sources. In El Salvador, geothermal energy is supplying 30% of the total electric energy used. However, at the global level, geothermal energy supplies less than 0.15% of the total energy supply. → Geothermal energy may be considered a nonrenewable energy source when rates of extraction are greater than rates of natural replenishment. However, geothermal energy has its origin in the natural heat production within Earth, and only a small fraction of the vast total resource base is being utilized today. Although most ge0thermal energy production involves the tapping of high heat sources; people are also using the low-temperature geothermal energy of groundwater in some applications. Geothermal Systems →A The average heat flow from the interior of the Earth is very low, about 0.06 W/m2.B This amount is trivial compared with the 177 W/m2 from solar heat at the surface in the United States. However, in some areas, heat flow is sufficiently high to be useful for producing energy. For the most part, areas of high heat flow are associated with plate tectonic boundaries. Oceanic ridge systems (divergent plate boundaries) and areas where mountains are being uplifted and volcanic island arcs are forming (convergent plate boundaries) are areas where this natural heat flow is anomalously high. C On the basis of geological criteria, several types of hot geothermal systems (with temperatures greater than about 80℃, or 176°F) have been defined, and the resource base is larger than that of fossil fuels and nuclear energy combined. A common system for energy development is hydrothermal convection, characterized by the circulation of steam and/or hot water that transfers heat from depths to the surface. D Geothermal Energy and the Environment → The environmental impact of geothermal energy may not be as extensive as that of other sources of energy, but it can be considerable. When geothermal energy is developed at a particular site, environmental problems include on-site noise, emissions of gas, and disturbance of the land at drilling sites, disposal sites, roads and pipelines, and power plants. Development of geothermal energy does not require large-scale transportation of raw materials or refining of chemicals, as development of fossil fuels does. Furthermore, geothermal energy does not produce the atmospheric pollutants associated with burning fossil fuels or the radioactive waste associated with nuclear energy. However, geothermal development often does produce considerable thermal pollution from hot waste-waters, which may be saline or highly corrosive, producing disposal and treatment problems. → Geothermal power is not very popular in some locations among some people. For instance, geothermal energy has been produced for years on the island of Hawaii, where active volcanic processes provide abundant near-surface heat. There is controversy, however, over further exploration and development. Native Hawaiians and others have argued that the exploration and development of geothermal energy degrade the tropical forest as developers construct roads, build facilities, and drill wells. In addition, religious and cultural issues in Hawaii relate to the use of geothermal energy. For example, some people are offended by using the "breath and water of Pele" (the volcano goddess) to make electricity. This issue points out the importance of being sensitive to the values and cultures of people where development is planned. Future of Geothermal Energy At present, geothermal energy supplies only a small fraction of the electrical energy produced in the United States. However, if developed, known geothermal resources in the United States could produce about 20,000 MW which is about 10% of the electricity needed for the western states. Geohydrothermal resources not yet discovered could conservatively provide four times that amount (approximately 10% of total U.S. electric capacity), about equivalent to the electricity produced from water power today.

In paragraph 1, the author introduces the concept of geothermal energy by

A．explaining the history of this energy source worldwide

B．arguing that this energy source has been tried unsuccessfully

C．comparing the production with that of other energy sources

D．describing the alternatives for generating electric power

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The Impossibility of Rapid Energy Transitions

[ A ] Politicians are fond of promising rapid energy transitions．Whether it is a transition from imported to domestic oil or from coal-powered electricity production to natural-gas power plants， politicians love to talk big．Unfortunately for them （and often the taxpayers）， our energy systems are a bit like an aircraft carrier: they are unbelievably expensive， they are built to last for a very long time， they have a huge amount of inertia （meaning it takes a lot of energy to set them moving ）， and they have a lot of momentum once they are set in motion．No matter how hard you try， you can"t turn something that large on a dime （10美分硬币 ）， or even a few thousand dimes．

[ B ] In physics， moving objects have two characteristics relevant to understanding the dynamics of energy systems: inertia and momentum．Inertia is the resistance of objects to efforts to change their state of motion．If you try to push a boulder （大圆石 ）， it pushes you back．Once you have started the boulder rolling， it develops momentum， which is defined by its mass and velocity．Momentum is said to be "conserved，" that is， once you build it up， it has to go somewhere．So a heavy object， like a football player moving at a high speed， has a lot of momentum-that is， once he is moving， it is hard to change his state of motion．If you want to change his course， you have only a few choices: you can stop him， transferring （possibly painfully） some of his kinetic energy （动能） to your own body， or you can approach alongside and slowly apply pressure to gradually alter his course．

[ C ] But there are other kinds of momentum as well．After all， we don"t speak only of objects or people as having momentum; we speak of entire systems having momentum．Whether it"s a sports team or a presidential campaign， everybody relishes having the big momentum， because it makes them harder to stop or change direction．

[ D ] One kind of momentum is technological momentum．When a technology is deployed， its impacts reach far beyond itself．Consider the incandescent （白炽灯的） bulb， an object currently hated by many environmentalists and energy-efficiency advocates．The incandescent light bulb， invented by Thomas Edison， which came to be the symbol of inspiration， has been developed into hundreds， if not thousands， of forms．Today， a visit to a lighting store reveals a stunning array of choices．There are standard-shaped bulbs， flame-shaped bulbs， colored globe-shaped bulbs， and more．It is quite easy， with all that choice， to change a light bulb．

[ E ] But the momentum of incandescent lighting does not stop there．All of those specialized bulbs ledto the building of specialized light fixtures， from the desk lamp you study by， to the ugly but beloved hand-painted Chinese lamp you inherited from your grandmother， to the ceiling fixture in your closet， to the light in your oven or refrigerator， and to the light that the dentist points at you．It is easy to change a light bulb， sure， but it is harder to change the bulb and its fixture．

[ F ] And there is more to the story， because not only are the devices that house incandescent bulbs shaped to their underlying characteristics， but rooms and entire buildings have been designed in accordance with how incandescent lighting reflects off walls and windows．

[ G ] As lighting expert Howard Brandston points out， “ Generally， there are no bad light sources， only bad applications．" There are some very commendable characteristics of the CFL [ compact fluorescent （荧光的） light bulb ]， yet the selection of any light source remains inseparable from the luminaire （照明装置 ） that houses it， along with the space in which both are installed， and lighting requirements that need to be satisfied．The lamp， the fixture， and the room， all three must work in concert for the true benefits of end-users．If the CFL should be used for lighting a particular space， or an object within that space， the fixture must be designed to work with that lamp， and that fixture with the room．It is a symbiotic （共生的 ） relationship．A CFL cannot be simply installed in an incandescent fixture and then expected to produce a visual appearance that is more than washed out， foggy， and dim．The whole fixture must be replaced-light source and luminaire-and this is never an inexpensive proposition．

[ H ] And Brandston knows a thing or two about lighting， being the man who illuminated the Statue of Liberty．

[ I ]Another type of momentum we have to think about when planning for changes in our energy systems is labor-pool momentum．It is one thing to say that we are going to shift 30 percent of our electricity supply from， say， coal to nuclear power in 20 years．But it is another thing to have a supply of trained talent that could let you carry out this promise．That is because the engineers，designers， regulators， operators， and all of the other skilled people needed for the new energy industry are specialists who have to be trained first （or retrained， if they are the ones being laid off in some related industry）， and education， like any other complicated endeavor， takes time．And not only do our prospective new energy workers have to be trained， they have to be trained in the right sequence．One needs the designers， and perhaps the regulators， before the builders and operators， and each group of workers in training has to know there is work waiting beyond graduation．In some cases， colleges and universities might have to change their training programs，

adding another layer of difficulty．

[ J ] By far the biggest type of momentum that comes into play when it comes to changing our energy systems is economic momentum．The major components of our energy systems， such as fuel production， refining， electrical generation and distribution， are costly installations that have lengthy life spans．They have to operate for long periods of time before the costs of development have been recovered．When investors put up money to build， say， a nuclear power plant， they expect to earn that money back over the planned life of the plant， which is typically between 40and 60 years．Some coal power plants in the United States have operated for more than 70 years!

The oldest continuously operated commercial hydro-electric plant in the United States is on New York"s Hudson River， and it went into commercial service in 1898．

[ K ] As Vaclav Smil points out， "All the forecasts， plans， and anticipations cited above have failed so miserably because their authors and promoters thought the transitions they hoped to implement would proceed unlike all previous energy transitions， and that their progress could be accelerated in an unprecedented manner．"

[ L ] When you hear people speaking of making a rapid transition toward any type of energy， whether it is a switch from coal to nuclear power， or a switch from gasoline-powered cars to electric cars， or even a switch．from an incandescent to a fluorescent light， understanding energy system inertia and momentum can help you decide whether their plans are feasible．

Not only moving objects and people but all systems have momentum．

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