全国英语等级考试教材第三级Unit18

[00:00.00] Chapter 18 Popular science [00:12.59]Unit 18 Popular Science [00:18.55]Conversations [00:22.02]1.Tang Ming and Du Hua,two college students,are discussing computer craze. [00:29.78]Now,Many students have computers. [00:35.34]A computer craze has hit the campus of many colleges of China. [00:41.59]yes,you are right. [00:45.06]If you enter a dormitory,You will find one or two computers there. [00:51.02]It is true that the computer has been used widely in students' studies. [00:57.68]But some students often play computer games. [01:03.24]Rigth.according to the survey, [01:07.68]computers greatly influence some students' studies. [01:12.96]In my university, [01:16.30]many young video addicts could indulge themselves in games all night long. [01:22.86]Oh.Fortunately,many universities and colleges are aware of such problems [01:30.51]and are planning to carry out projects to correct this phenomenon. [01:36.86]It seems to me that the campus computer problems [01:41.93]are not a question of the computer itself but of the way of using it. [01:47.78]I agree. [01:50.84]We are sure tha tcolleges and universities can find a good solution to these problems. [01:58.49]2. Wu Li is a salesman. Ma Gang is a customer. [02:04.84]They are talking about exchanging a computer. [02:09.38]What can I do for you? [02:13.33]I bought a computer here last Friday and now it simply does not work. [02:19.57]What's wrong with it? [02:23.12]I'm not sure. [02:26.18]When I turn it on,there's only sould but no words. [02:31.51]Is the screen clear? Not very clear. [02:36.34]Did you try it here before you took it home? [02:41.49]yes.It was all right. [02:45.15]But when it got to my office,it didn't work properly. [02:50.11]It's unreasonalbe. [02:53.95]Can you replace it with another one? [02:57.89]I'm afraid not. [03:01.37]Would you send the computer in and we have it checked first? [03:07.53]Then we'll see what we can do about it. [03:11.29]3. Tom and Susan are in Tom's sports car. [03:17.54]They are at a petrol station. [03:21.40]Three gallons of super,please. [03:25.66]Three gallons of super.Yes,sir. [03:29.92]Tom...why don't we get small family car? [03:35.38]What? You mean,sell my sports car? Never! [03:40.53]But it's expensive to run and it's old. [03:46.17]You bought it long before. [03:50.30]Er...excuse me.That's $5.sir. [03:55.26]here you are.Oh,and would you check my battery,please? [04:00.59]Check the battery,sir? Certainly. [04:04.45]Don't you remember? [04:07.98]It broke down just before we got married [04:13.23]and it was in the garage for a whole week! [04:17.99]This is a wonderful car! It always starts first time! [04:23.34]The battery's all right,sir. Thank you. [04:28.09]It didn't start first time yesterday morning! [04:33.42]That was only because it was so cold! [04:37.66]It's a wonderful engine.just listen to it when I start now! [04:42.91](Presses starter.Sound of engine turning over but not starting.) [04:49.46]I'm listening,Tom. [04:53.62]Passage Electricity [04:58.58] If you were thirsty,and took a cup to the kitchen sink, [05:04.04]you might first turn the tap on just a little way, [05:09.39]so that only a thin stream of water came form it. [05:14.75]Then you would turn the tap a bit farther. [05:19.79]Not only would there be more water,but also it would come out with greater force. [05:27.84]If you turned it on as far as it would go , [05:32.90]you would get no water in your cup at all, [05:37.66]for it would come form the tap in so powerful a jet [05:43.41]that it would bounce straight out of the cup again, [05:48.16]and most likely drench you. [05:52.52] In that stream of water,then,are three things-- [05:58.09]or rather,two things and their result. [06:03.55]Firstly,the amount or quantity,or current of water. [06:10.42]Secondly,the pressure pushing it. [06:15.46]And thirdly,the power of the jet,which is the result, [06:21.62]or pruduct of the current of water and the force pushing it. [06:27.68]Electrical power [06:31.44] Although this is not quite the same as in electricity, [06:37.40]it helps in understanding amps,volts and watts. [06:43.46]For the volt is the unit of electrical pressure,or force. [06:49.84]The amp (short for ampere) is the unit of electrical current, [06:56.97]while the watt is the unit of electrical power. [07:01.93] A watt is the power given by an ampere of current [07:07.86]flowing in a circuit at a pressure of one volt. [07:13.01]So the more the volts and amps there are,the more watts. [07:19.85]As in that water tap,the more current there is, [07:25.41]and the more pressure,then the greater the resulting power. [07:31.34] The word "pressure" is not auite correct,however,when used about volts. [07:38.81]They are better described as units of force-- [07:44.07]scientists and engineers cal them units of "electromotive force",or E.M.F. [07:54.23] Resistance [07:58.20] When you pump up your bicycle tyre,you use force,or pressure, [08:04.96]to push air into the inner tube. [08:09.51]But the air in there already pushes back against you. [08:15.88]In much the same way,when you push a current of electricity through a wire, [08:23.43]there is a kind of push-back,called "resistance", [08:29.20]set up by the metal of which the wire is made. [08:34.25] Just as the units of force,current and power ahve names, [08:40.91]so has the unit of electrical resistance.It is called the "ohm". [08:48.27]Resistance of metals [08:52.35]Every metal ahs its own resistance to the passage of an electrical current through it. [08:59.90]The lower the resistance of a metal,the better it is as a carrier, [09:06.66]or "conductor" of electrical energy. [09:11.63]For if you have to use up power in overcoming this resistance, [09:17.98]there is so much the less for you at the other end of the conductor. [09:24.24] The length of pieces of wire of the same diameter, [09:29.89]each piece having a resistance of one ohm, [09:35.45]will depend on the metal of which they are made. [09:40.49]Again,for the same diameter, [09:45.04]a wire of low resistance will be longer than one of high resistance. [09:51.99]A copper wire will be longer than one of iron, [09:57.73]or lead,or nickedl,for its resistance is very low, [10:03.69]and not much energy is needed to overcome it. [10:08.65] For this reason copper is used in making wires, [10:14.53]cables and overhead lines for carrying electrical current. [10:20.59] Aluminium is another good conductor with a low resistance. [10:26.83]Being light in weight,it is often used for overhead lines, [10:33.08]such as you see slung in graceful curves between pylons, [10:39.14]but being a soft metal it usually has a steel wire core to give it strength. [10:46.50] Sometimes,however,wires of high resistance are put to special uses. [10:54.37]When electrical energy is taken up in overcoming the resistance of a wire, [11:01.42]it produces heat. [11:05.08]this makes the sire redhot,as in an electric radiator, [11:11.74]or while-hot,as in the filament of a lamp. [11:16.91]Thus from metals of high resistance,we can get either heat or light for our use. [11:25.37]Words and Expressions [11:29.03]thirsty tap bounce [11:31.71]adj.口渴的 n.龙头 v.弹出 [11:34.39]drench amp volt [11:36.71]v.使浸透，弄湿 n.(电)安培 n.(电)伏特，伏 [11:39.04]watt circuit pump [11:41.41]n.(电)瓦特 n.电路;线路 v.为...打气 [11:43.79]wire resistance ohm [11:46.17]n.电线 n.(电)电阻 n.(电阻单位)欧姆 [11:48.55]conductor diameter lead [11:51.28]n.(电)导体 n.直径 n.铅 [11:54.00]nickel cable aluminium [11:56.43]n.镍 n.(电)电缆 n.铝 [11:58.86]sling pylon [12:00.90]v.吊 n.架高压电缆的铁塔 [12:02.94]radiator filament [12:05.16]n.散热器 n.灯丝 [12:07.38]Exercises Section I Listening Comprehension [12:14.04]Listen to the record. [12:17.99]Answer each question by choosing A,B,C or D from the possible choices. [12:25.93] 1.I need to get car insurance.You got any ideas? [12:34.39]Well,you could try my company.It seems to have fair rates. [12:39.95]Sir.Your bags ar 40 ponds overwight.You are allowed only 25 pounds of baggage. [12:49.70]Well then,how much do I owe you? [12:53.46]You're putting on a little weight,aren't you? I know.Don't remind me. [13:01.22]I'm starting a new diet today. [13:05.97]Where can I exchange some money? [13:11.61]You'll have to go to the Bank of China,but it closes at 5:00 p.m. [13:17.86]I'm a scientist.I've just finished a paper on computer 5. [13:25.30]Oh? That's my field,too.I work for an institute. [13:30.76]How exactly do you figure out the car fares? [13:37.53]Well,the first five kilometres are ten dollars [13:42.07]and every extra kilometre costs you one dollar. [13:46.80]The dictionary is $58 and the textbook is $25. [13:54.87]Here's a hundred dollar bill. [13:58.53]How long will it take you to repair my computer? [14:04.70]I'll call you when it's ready,but it shouldn't take longer then two weeks. [14:10.65]How much time did you have for writing the composition? [14:16.82]We were given 2 hours,but I finished in less than half the time. [14:22.98]What do you think of my article? The ideas are good. [14:29.83]If I were you,I'd rewrite the last two paragraphs to make it better. [14:36.59]B Everyone seems to be on a diet. [14:42.16]have you noticed that,Jane? [14:45.68]Everyone seems to be talking about diets. [14:50.93]A neighbour of mine is on an orange diet. [14:55.50]She eats an orange for breakfast,an organge for lunch,and two oranges for dinner. [15:02.16]That's bad for the health! Has she lost any weight? [15:07.81]She doesn't look any thinner,but she hasn't been on the diet long. [15:13.27]A friend of mine eats eggs for breakfast,lunch and dinner. [15:20.35]He never eats anything but eggs. [15:25.20]That's bad for the heart! [15:29.04]Eggs have a lot of protein and protein is good for losing wight. [15:34.82]To many eggs are bad for the heart. [15:38.95]I've read that,too.But eggs are cheaper than steak. [15:45.21]An uncle of mine doesn't eat anything but steak. [15:50.78]He eats steak for breadkfast. [15:55.04]The best way to lose weight is to eat less and exercise more. [16:00.91]C You should be careful with fires. [16:05.96]People who are not careful cometimes cause fires that burn buildings or forests. [16:13.90]If youa re ever in building,Crawl on the floor to a door and get out. [16:20.98]The smoke and heat from the fire are in the upper part of a room. [16:27.64]The air near the floor is cooler and fresher. [16:33.10] If your clothing get on fire, [16:37.46]roll on the ground or wrap yourself in a blanket to shut out the air. [16:44.41]With no air,the fire will go out. [16:49.45] Firemen sometimes put out fires by spraying water on them. [16:55.90]The water cools the burning material so that the fire goes out. [17:02.25]Supplementary Reading [17:05.80]Computers and Crime [17:09.75]No one who reads the newspapers can doubt the seriousness of this country. [17:16.23]Not a day goes by without numberous robberies,rapes,and murders being reported. [17:23.59]In amny cities,It's extremely dangerous to walk the street at night. [17:29.55] Crime is a complex problem with many causes. [17:35.29]Poverty,unemployment,conditions in the cities, [17:40.73]and increasing disregard for authority all play their roles [17:46.76]and no single remedy is going to solve the problem overnight. [17:52.33] But perhaps at least one of the causes can be dealt with [17:57.97]-- the inefficiency of the criminal justice system. [18:03.12]For instance, [18:06.28]the police usually are able to solve only a fraction of the crimes committed. [18:13.41]And offenders are apprehended, [18:17.25]there is usually a long delay in trial and sentencing. [18:22.50]During the delay,the offenders may be out on bail committing more crimes. [18:29.73] Much police work concerns information--information about stolen property, [18:37.28]fugitives from justice,the methods of operation of known criminals. [18:43.76]The computer can make an important contribution to processing [18:49.40]this information effectively and efficiently. [18:54.37] Unfortunately,there is almost no other area in which computers inspire such fear. [19:02.23]The reason is obvious: [19:06.20]the police can initiate proceedings that can take a person's liberty away. [19:12.65]And,sometimes with good reason, [19:16.91]not everyone is convinced that those proceedings will be carried out fairly. [19:23.68]Even worse,the police keep records that can haunt us the rest of our lives. [19:30.91]Even those people who have the most to fear from crime may fear [19:37.37]even more anything that increase the effectiveness fo the police. [19:43.14] (The fact taht large segments of the population do distrust the police [19:49.98]is one more reason there will be no easy solutions to the problem of crime.) [19:56.75] In one way,the computer can be considered a mixed blessing for law enforcement. [20:03.91]To be sure,it helps the police solve crimes and apprehend criminals. [20:10.15]But it also opens up a whole new world of ways to commit crimes. [20:16.52]As far back as 1974,authorities estimated that over 200 million [20:24.57]were being lost each year through computer-related crime. [20:30.03]That figure certainly ahs not diminished in the intervening years.

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