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
The prefix Mach is used to describe supersonic speed. It was named for Ernst Mach (1838—1916), a Czech-born Austrian physicist,
The prefix Mach is used to describe supersonic speed. It was named for Ernst Mach (1838—1916), a Czech-born Austrian physicist,
admin
2015-06-27
53
问题
The prefix Mach is used to describe supersonic speed. It was named for Ernst Mach (1838—1916), a Czech-born Austrian physicist, who contributed to the study of sound. When twice the speed of sound, it is Mach 2. When it is near but below the speed of sound, its speed can be designated at less than Mach 1, for example, Mach 0. 90. Mach is defined as "the ratio of the velocity of a rocket or a jet to the velocity of sound in the medium being considered".
When a plane passes the sound barrier — flying faster than sound travels, listeners in the area hear thunderclaps, but the pilot of the plane does not hear them.
Sound is produced by vibrations of an object and is transmitted by alternate increase and decrease in pressure that radiate outward through a material media of molecules — somewhat like waves spreading out on a pond after a rock has been tossed into it.
The frequency of sound is determined by the number of times the vibrating waves undulate per second and is measured in cycles per second. The slower the cycle of waves, the lower the frequency. As frequencies increase, the sound is higher in pitch.
Sound is audible to human beings only if the frequency falls within a certain range. The human ear is usually not sensitive to frequencies of fewer than 20 vibrations per second, or more than about 20, 000 vibrations per second — although this range varies among individuals. Anything at a pitch higher than the human ear can hear is termed ultrasonic.
Intensity, or loudness, is the strength of the pressure of these radiating waves and is measured in decibels. The human ear responds to intensity in a range from zero to 120 decibels. Any sound with pressure over 120 decibels is painful to the human ear.
The speed of sound is generally placed at 1, 088 feet per second at sea level at 32 degrees Fahrenheit. It varies in other temperatures and in different media. Sound travels faster in water than in air, and even faster in iron and steel. It travels a mile in 5 seconds in air, it does a mile under water in 1 second, and it travels through iron in 1 /3 second. It travels through ice cold vapor at approximately 4, 708 feet per second; ice-cold water, 4,938; granite, 12,960; hardwood, 12,620; brick, 11,960, glass, 16,410 to 19,690; silver, 8,658; gold, 5,717.
At which frequency is the sound audible to human beings?
选项
A、Fewer than about 20 vibrations per second.
B、More than about 20,000 vibrations per second.
C、About in a range of 20 and 20,000 vibrations per second.
D、120 vibrations per second.
答案
C
解析
第五段第二句提到,人的耳朵可以听到的声音为每秒频率在20次到2万次的震动,故答案为[C]。
转载请注明原文地址:https://kaotiyun.com/show/nTXK777K
0
专业英语四级
相关试题推荐
Whetheranoperationshouldbeperformedinthiscase______verymuchonthepatient’sgeneralcondition.
Atthebeginningofthepassage,theauthorindicatesthat_____.WhichofthefollowingadjectivescanbestdescribeAmsterda
Foodcanbeproducedmuchmorecheaplytodaybecauseofimprovedfertilizersandbettermachinery.However,someofthemethods
InarecentbookentitledThePsychicLifeofInsects,ProfessorBouviersaysthatwemustbecarefulnottocreditthelittlew
ManypeopleinvestinthestockmarkethopingtofindthenextMicrosoftandDell.However,Iknow【C1】______personalexperie
Shynessisthecauseofmuchunhappinessforagreatmanypeople.Shypeopleare【C1】______andself-conscious;thatis,theyar
Thekeytopleasantmusicmaybethatitpleasesourneurons.Anewmodelsuggeststhat【C1】______musicalintervalstriggerarhy
Wecan’tjust_________theseobjectionsoff.
Globalwarmingisalreadycuttingsubstantiallyintopotentialcropyieldsinsomecountries—tosuchanextentthatitmaybea
Thegovernmentisthinkingof______heavytaxesoncigarettestoraiseextrarevenue.
随机试题
面部“危险三角区”的疖最危险的并发症是()。
严重烧伤休克期一般可延至伤后()
下列火灾预警能力的各项指标,定义正确的是()。
申请代理报检注册登记的单位应当具备的条件包括()。
2014年甲公司房产原值1000000元,已提取折旧350000元。已知从价计征房产税税率为1.2%,当地规定的房产税扣除比例为30%,甲公司当年应缴纳房产税税额的下列计算中,正确的是()。
湖南省最具影响力的戏曲剧种是()。
【永贞革新】扬州大学2013年中国古代史真题;湖南师范大学2016年中国史综合真题;华中师范大学2017年中国史基础真题;南京大学2017年中国古代史基础真题
设机器码的长度为8,x为带符号纯小数,y为带符号纯整数,[X]原=11111111, [Y]补=11111111,则x的十进制真值为(3),y的十进制真值为(4)。
设某二叉树的后序序列与中序序列均为ABCDEFGH,则该二叉树的前序序列为()。
用“综合业务数字网”接入因特网的优点是上网通话两不误,它的英文缩写是()。
最新回复
(
0
)