首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
A、By producing pressure waves going in the opposite direction. B、By mixing new sound waves with the noise and sending them out t
A、By producing pressure waves going in the opposite direction. B、By mixing new sound waves with the noise and sending them out t
admin
2013-01-22
67
问题
The idea of fighting a noise by making more noise sounds strange, but that’s exactly what motor engineers are doing in Germany and some other countries.
Carmakers’ research and development laboratories have already proved that mixing in more noise with the help of loudspeakers can reduce the unwanted noise.
Physicists have known about the technique for a long time. Sound is made up of pressure waves in the air. If two sound waves of the same frequency mix so that the highest point of one wave happens at the same time with the lowest point of the other wave, the result is no sound. Therefore, by producing a perfect copy of the noise and delaying it by half a wave cycle, we can kill the unwanted noise. Using this technique many carmakers are racing to develop noise-killing systems both inside and outside the cars.
Another good thing about the use of noise-killing systems is that it saves the need for a silencer, which not only reduces the weight of a car, but also makes the motor burn less oil and work better.
Some engineers believe that the noise-killing system will be used in most cars by 1996. But the carmakers haven’t decided if they will put it into production because it would add several hundred dollars to the cost of their cars.
Questions 29 to 31 are based on the passage you have just heard.
29. Which gives a general idea of how the noise-killing system works?
30. What can the noise-killing system do besides its main function?
31. Why isn’t the noise-killing system yet popular?
选项
A、By producing pressure waves going in the opposite direction.
B、By mixing new sound waves with the noise and sending them out together.
C、By mixing high-frequency sound waves with low-frequency ones.
D、By making a copy of the unwanted sound waves and letting it out a little later.
答案
D
解析
选项均以“By+doing”开头表明,本题考查方式方法。短文中提到噪声消除系统的工作原理:如果两种相同频率的噪音混合,一种声波的最高点同时碰到另一种声波的最低点,噪音就消失了,接着提到对噪音进行完美复制,把复制的噪音推迟半个波周期,我们就可以消除不想要的噪音,D)的内容正是对此的同义转述,故答案为D)。
转载请注明原文地址:https://kaotiyun.com/show/KHI7777K
0
大学英语六级
相关试题推荐
A、Enjoyable.B、Inspiring.C、Moving.D、Dull.D对话中女士提到Ifeltsleepy(我昏昏欲睡),DDull对应sleepy,故为答案。
CordiaHarringtonwastiredofstandingupalldayandsmellinglikeFrenchfriesatnight.Apropertydeveloper,shealsoowned
A、StayingatHomeB、WorkandHappinessC、WorkandProductivityD、AmericansandEuropeansB选项中实词的首字母都大写表明,本题考查短文标题。短文从各个方面对美国人和欧洲
A、Impolitebutcommon.B、Annoyingbutcommon.C、Annoyinganddislikable.D、Commonandacceptable.A选项均为形容词词组表明,本题可能考查对某件事情的看法。男士
A、Atteatimethisafternoon.B、AtlunchnextTuesday.C、AtlunchonWednesday.D、AtteatimeonWednesday.C对话中女士询问theteatimeth
A、Hewilltakeacoffeebreak.B、Hewillkeeponworking.C、Hewillgoforawalk.D、Hewillbeginwiththereport.B由男士提到的Iwis
A、Clearandwarm.B、Cloudyandwet.C、Coldandsnowy.D、Hotanddry.B男士说这一周天气一直不好,女士说每天天空昏暗还下雨,可知最近天气多云雨,故选B项。
Peopleoftenmakemistakesintheir__________asthingsinmanycasesturnouttheoppositetotheirwishes.
A、Exercisingtheentirebody.B、Havingyourbloodpressuretakendaily.C、Losingweightpriortoexercising.D、Weighinginbefor
随机试题
15岁女孩,骑自行车急转弯时不慎撞到护栏上,自觉外阴疼痛难忍并肿胀而就诊。根据女性外阴解剖学特点,可能发生的是()
在草图管理工具条中什么图标重定位视图,使得当草图激活时直接在草图平面观察草图?
哪一种药物不是治疗心力衰竭的常规药
种公猪,3岁,精神沉郁,减食,脊背拱起,行动困难,腰部敏感,疼痛,尿量少,尿沉渣中有大量肾上皮细胞、白细胞、红细胞,可能的疾病是
黏膜良性类天疱疮常见白斑常见
在十八大报告和十八届三中全会通过的《中共中央关于全面深化改革若干重大问题的决定》中,都反映出执政党和政府社会政策目标和理念的提升,提出了()
下列说法不正确的是()。
在传染病的发生、发展过程中,从病原体侵入人体到最初出现症状的这段时间称为()。
设直线y=ax与抛物线y=x2所围成的图形面积为S1,它们与直线x=1所围成的图形面积为S2,且a<1.(1)确定a,使S1+S2达到最小,并求出最小值;(2)求该最小值所对应的平面图形绕x轴旋转一周所得旋转体的体积.
A、Hethinksit’sstupidtobuyacupcakeinthemorning.B、Hehasadifferentopinionfromthemajority.C、Hethinkshavingone
最新回复
(
0
)