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
To fight a noise by making more noise sounds strange, but that’s exactly what motor engineers are doing in Germany and some othe
To fight a noise by making more noise sounds strange, but that’s exactly what motor engineers are doing in Germany and some othe
admin
2009-09-15
60
问题
To fight a noise by making more noise sounds strange, but that’s exactly what motor engineers are doing in Germany and some other countries.
Carmaker’s research and development laboratories have already proved that mixing 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 (频率) mix so that the highest point of one wave happens at the same time as 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 (周期), we can kill the unwanted noise. Using this technique many carmakers are racing to develop noise killing systems (系统) 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; this not only reduces the weight of a car, but also makes the motor burn less fuel and work better.
Some engineers believe that the noise killing system will be used in most cars within a few years. But the carmakers haven’ t decided if they will carry it into production because it would add several hundred dollars to the cost of their cars.
选项
A、By producing pressure waves going in the opposite direction.
B、By mixing high frequency sound waves with low frequency sound waves.
C、By mixing new sound waves with the noise and sending them out together.
D、By making copies of the unwanted sound waves and letting them out a little later.
答案
D
解析
从文章第二段第四句,Therefore,by producing a perfect copy of the noise and delaying it by half a wave cycle, we can kill the unwanted noise可知,降低噪音的原理是产生一个完全相同的声波,然后让它延迟半个周期,我们就可以消除令人讨厌的噪声了。所以正确的答案为D。
转载请注明原文地址:https://kaotiyun.com/show/Vgfd777K
本试题收录于:
公共英语二级笔试题库公共英语(PETS)分类
0
公共英语二级笔试
公共英语(PETS)
相关试题推荐
Eversinceshestartedpianolessonsattheageoften,Carolhaslovedmusic.Asshegotolder,shedecidedtobecomeamusict
【B1】【B19】
TheUnitedStatesiswell-knownforitsnetworkofmajorhighwaysdesignedtohelpadrivergetfromoneplacetoanotherinthe
Iamusedtotakingabushome,butlastnightitwasrainingandIdecidedtorideinataxi.Istoodontheside-walk【B1】to
Theyoungsoldier______.WhydidLincolnaddedintheletter"writtenforyoursonbyAbrahamLincoln"?becausehewanted____
Thetwoboyslookexactly______.
InJanuary2002,duringthefirstweeksofasix-monthstayattheChildren’sHospitalofPhiladelphiaforleukemia(白血病)treatm
TheRedCrossisaninternationalorganizationwhichcaresforpeoplewhoareinneedofhelp.AmaninParishospitalwhoneeds
Itisnecessarythatanefficientworker______hisworkontime.
Whatexactlydoesthemanwanttofindout?
随机试题
A.阴阳相互交感B.阴阳对立制约C.阴阳互根互用D.阴阳相互转化“寒极生热,热极生寒”的机理是
关于儿茶酚胺与β受体结合后产生的效应,下列哪项叙述是错误的
此时首先应考虑的检查为为支持诊断而应选择的检查方法为
男性,62岁。头晕、乏力半年,近1个月症状加重,间有低热,四肢酸痛来诊。体检:体温38℃,重度贫血貌,下肢皮肤散在出血点;颈部可扪及花生仁大小淋巴结2枚,脾肋下2cm。化验:Hb50g/L,WBC2.3×109/L,PLT45×109/L,血片中
革兰氏阴性菌的黏附因子是()。
下面关于渗井的描述错误的是()。
某企业2018年年初拥有房产3栋,分别为:厂房1栋,原值500万元,已经使用5年,预计还可以使用20年;办公楼l栋(10层),原值1000万元,已经使用1年,预计还可以使用19年;仓库1栋,原值150万元,已经使用10年,预计还可以使用15年。2018年6
下列代理行为中,属于滥用代理权的有()。
某公司在2000年1月1日平价发行新债券,每张面值1000元,票面利率10%,5年到期,每年12月31日付息(计算过程中至少保留小数点后4位,计算结果取整)。要求:(1)2000年1月1日到期收益率是多少?(2)假定2001年1月1日的市场利率下降到
所谓信息系统集成是指()。
最新回复
(
0
)