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 mixing high frequency sound waves with low frequency sound waves. B、By producing pressure waves going in the opposite direc
A、By mixing high frequency sound waves with low frequency sound waves. B、By producing pressure waves going in the opposite direc
admin
2013-05-04
33
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.
Carmaker’s 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 in 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.
选项
A、By mixing high frequency sound waves with low frequency sound waves.
B、By producing pressure waves going in the opposite direction.
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
转载请注明原文地址:https://kaotiyun.com/show/8HB7777K
0
大学英语六级
相关试题推荐
OnepositiveconsequenceofourcurrentnationalcrisismaybeatleastatemporaryreductioninHollywood’scultureofviolence
Businessandgovernmentleadersconsidertheinflationratetobeanimportantindicator.Inflationisaperiodofincreased【C1】
Businessandgovernmentleadersconsidertheinflationratetobeanimportantindicator.Inflationisaperiodofincreased【C1】
Ifyouareanythinglikeme,youleftthetheaterafterSexandtheCity2andthought,thereoughttobealawagainstalooks-
A、Arealisticgoalforlearnersistoreachacertainleveloflanguageproficiency.B、Learnerscanachievenative-likepronunci
Gotapenhandy?Tobestestimateyourstart-upcosts,you’llneedtomakealistandthemoredetailedthebetter.Asmartway
A、Theyhaveaprivatetutor.B、Theygotoaregularschool.C、Theyattendaspecialschool.D、Theyaretaughtbytheirparents.
A、Problemswithlivinginanapartment.B、Thechancetofindapart-timejob.C、Thecostofrentnearuniversities.D、Asearchf
A、ShehasgonetoAmericaonbusiness.B、Shemaygetmarriedinafewmonths.C、ShehasdoneSarahabigfavor.D、Shehasdated
A、He’llgivethequizatalatertime.B、Thequizwillbeveryshort.C、Thequizwon’tbereadyuntilThursday.D、He’llscoreth
随机试题
设cmd=who,以下4个命令中,执行结果与其他不同的是_______。
A.珠蛋白合成障碍B.血红素合成障碍C.DNA合成障碍D.铁利用障碍E.干细胞造血障碍缺铁性贫血是
脾虚证,采用“补母泻子法”,本经、他经分别应取()。
在计算会计政策变更的累积影响数时,其中“计算差异的所得税影响金额”是指如果采用应付税款法时,应调整“应交税费”科目,在采用纳税影响会计法时,应调整“递延税款”科目。()
阅读以下文章,回答问题:地震发生时,最基本的现象是地面的连续振动,主要是明显的晃动。极震区的人在感到大的晃动之前,有时首先感到上下跳动。这是因为地震波从地内向地面传来,纵波首先到达的缘故。横波接着产生大振幅的水平方向的晃动,是造成地震灾害的主要原因。
患者,男性,38岁。被人用刀划伤左面部,流血不止。检查见左耳前区皮肤有长约6cm的纵行伤口,深达肌肉前层,创缘整齐,有活动性出血。此患者最确切的诊断是()。
设函数μ=f(x,y)具有二阶连续偏导数,且满足等式=0,确定a,b的值,使等式通过变换ξ=x+ay,η=x+by可化简为=0。
Describeachildyoulike.Youshouldsay:whothischildiswhatyourrelationshipwiththischildiswhathe/sheislikeande
Formany,thepursuitofhappinessisalsothepursuitofprosperity.PartoftheAmericandreamistheabilitytoprovide【M1】__
Themajorcauseof"forgetting"isfailuretolearnthematerial【B1】______inthefirstplace.However,weforgetata【B2】______r
最新回复
(
0
)