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
Radio and Television Radio and television were major agents of social change in the 20th century. Radio was once the center
Radio and Television Radio and television were major agents of social change in the 20th century. Radio was once the center
admin
2010-07-24
90
问题
Radio and Television
Radio and television were major agents of social change in the 20th century. Radio was once the center for family entertainment and news and television enhanced this revolution by adding sight to sound. Both opened the windows to other lives, to remote areas of the world, and to history in the making. News coverage changed from early and late editions of newspapers to broadcast coverage from the scene. Play-by-play sports broadcasts and live concerts enhanced entertainment coverage. For many, the only cultural performances or sports events they would ever hear or see would come from the speakers or the screens in their living rooms. Each has engaged millions of people in the major historical events that have shaped the world.
If people could look at the sky and see how it is organized into frequency" bands used for different purposes, they would be amazed. Radio waves crisscross (十字形) the atmosphere at the speed of tight, delivering incredible amounts of information—navigational data, radio signals, television pictures—using devices for transmission and reception designed, built, and refined by a century of engineers.
Key figures in the late 1800s included Nikola Tesla, who developed the Tesla coil, and James Clerk Maxwell and Heinrich Hertz, who proved mathematically the possibility of transmitting electromagnetic signals between widely separated points. It was Guglielmo Marconi who was most responsible for taking the theories of radio waves out of the laboratory and applying them to practical devices. His "wireless" telegraph demonstrated its great potential for worldwide communication in 1901 by sending a signal—the letter "s"—in Morse code a distance of 2 000 miles across the Atlantic Ocean. Radio technology was just around the comer.
Immediate engineering challenges addressed the means of transmitting and receiving coded messages, and developing a device that could convert a high-frequency oscillating (振荡的) signal into an electric current capable of registering as sound. The first significant development was "the Edison effect", the discovery that the carbon filament (灯丝) in the electric light bulb could send out a stream of electrons to a nearby test electrode if it had a positive charge. In 1904, Sir John Ambrose Fleming of Britain took this one step further by developing the diode (二极管) which allowed electric current to be detected by a telephone receiver. Two years later, American Lee De Forest developed the triode (三极管), introducing a third electrode (the grid) between the filament and the plate. It could amplify a signal to make live voice broadcasting possible, and was quickly added to Marconi’s wireless telegraph to produce the radio.
Radio development was prevented by restrictions placed on airwaves during World War I. Technical limitations were also a problem. Few people had receivers, and those that did had to wear headphones. Radio was seen by many as a hobby for telegraphy fans. It would take a great deal of engineering before the radio would become the unifying symbol of family entertainment and the medium for news that was its destiny.
In the mid-1920s, technical developments expanded transmission distances, radio stations were built across the country, and the performance and appearance of the radio were improved. With tuning circuits, capacitors, microphones, oscillators, and loudspeakers, the industry blossomed in just a decade. By the mid-1930s almost every American household had a radio. The appearance of the transistor in the 1950s completely transformed its size, style, and portability.
Both television and radar were logical byproducts of the radio. Almost 50 years before television became a reality, its fundamental principles had been independently developed in Europe, Russia, and the United States. John Baird in England and Charles Jenkins in the United States worked independently to combine modulated light and a scanning wheel to reconstruct a scene. In 1925, Baird succeeded in transmitting a recognizable image.
Philo T. Farnsworth, a 21-year-old inventor from Utah, patented a scanning ray tube, and Vladimir Zworykin of RCA devised a superior television camera in 1930. Regularly scheduled broadcasts started shortly thereafter, and by the early 1940s there were 23 television stations in operation throughout the United States.
Shortly after World War Ⅱ, televisions began to appear on the market. The first pictures were faded and flickering, but more than a million sets were sold before the end of the decade. An average set cost $500 at a time when the average salary was less than $3 000 a year. In 1950 engineers perfected the process of production and prices dropped to $200 per set. Within 10 years 45 million units were sold.
A study of how human vision works enabled engineers to develop television technology. Images are retained in a viewer’s eye for only a fraction of a second after they strike it. By displaying images piece by piece at sufficient speed, the illusion of a complete picture can be created. By changing the image on the screen 25 to 30 times per second, movement can be realistically represented. Early scanning wheels slowly built a picture line by line. In contrast, each image on a modern color television screen is comprised of more than 100 000 pixels (像素), arranged in several hundred lines. The image displayed changes every few hundredths of a second. For a 15-minute newscast, the television must accurately process more than 1 billion units of information. Technical innovations that made this possible included a screen coated with millions of tiny dots of fluorescent compounds that emit light when struck by high: speed electrons.
Today this technology is in transition again, moving away from conventional television waves and on to separate digital signals. This holds the potential for making television interactive—allowing a viewer to play a game or order action replays. Cathode ray tubes with power-hungry electron guns are giving way to liquid crystal display (LCD) panels. Movie-style wide screens and flat screens are readily available. Digital signals enable High Definition Television (HDTV) to have almost doubled the usual number of pixels, giving a much sharper picture. The appearance of cable television and advances in fiber-optic technology will also help lift the present bandwidth (带宽) restrictions and increase image quality.
The major difference between radio and television is ______ .
选项
A、whether they can broadcast cultural performances
B、whether they may attract millions of people in the great historical events
C、whether they open the windows to remote areas of the world
D、whether they may offer sights to the people
答案
D
解析
根据题干中的关键词major difference定位到文章首段第二句:Radio was once the center for family entertainment and news and television enhanced this revolution by adding sight to sound。收音机曾经是家庭娱乐和获得新闻的中心途径,然而通过为声音配上图像,电视将这一革命进一步深入。由此可以推断出收音机和电视的主要区别在于能否提供图像,所以选项D)正确。
转载请注明原文地址:https://kaotiyun.com/show/DtN7777K
0
大学英语四级
相关试题推荐
Incitieswithrentcontrol,thecitygovernmentsetsthemaximumrentthatalandlordcanchargeforanapartment.Supporterso
____________(她被眼前的情景吓的)thatshecouldnotspeakawordforseveralminutes.
Airportistransportationcenterusedforthelandingand【B1】______ofaircraft.Airportsprovidetransportationnotonlyforpeo
A、Checkwiththeemploymentresourcecenteratschool.B、Sendherresumestoallthemostprominentaccountingfirms.C、Resortt
A、Shewantsthemantowait.B、Sheisreadynow.C、Shehasdecidednottogo.D、Shethinksthemanshouldchangetheclothes.A
Noorganofthebodyisless【S1】______thantheskin.Oneofourbiggestandbusiestorgans,it【S2】______thestateofourhealth,
Manyteachersbelievethattheresponsibilitiesforlearningliewiththestudent.【C1】______alongreadingassignmentisgiven,
A、Hecouldn’tdecideonatopicforhispaper.B、Hethoughthispaperwaslate.C、Hehadn’theardfromhisfamilyinawhile.D、
FifteenyearsagoMasco,asmallfamilyfirm,suddenlygrewfast.Asitgrew,themanagementrealizedthatchangeswereneeded.
FifteenyearsagoMasco,asmallfamilyfirm,suddenlygrewfast.Asitgrew,themanagementrealizedthatchangeswereneeded.
随机试题
下列选项中,()不属于消防联动控制器的主要功能。
在为VIP宾客提供服务时,茶艺师应根据VIP宾客的()和茶艺馆的规定配备茶品。
金属烤瓷固定桥的瓷折裂和剥脱的原因可能是
根据《民事诉讼法》的规定,我国法院与外国法院可以进行司法协助,互相委托,代为一定的诉讼行为。但是在下列哪些情况下,我国法院应予以驳回或说明理由退回外国法院?
热补偿的主要方法有两种:其一是依靠弯管的自然补偿,通常当管路转角不大于150度时,均能起到一定的补偿作用:其二是利用补偿器进行补偿,主要有()、波形及填料3种补偿器。
计算机辅助工程网络计划编制的意义是( )。
根据现行企业所得税的规定,下列关于企业研究开发。新产品、新技术、新工艺所发生的各项费用的表述,不正确的是()。
astute service providers realize that the continued support of legacy X.25 and asynchronous network element using separate opera
YouwillhearatelephoneconversationaboutajourneytoNewYork.Listenandcompletequestions16-20.Youwillheartheconve
美国人强调效率、竞争和独创性,而中国人则将严谨规划放在首位,鼓励团队成员之间的密切合作和无私奉献。在美国学校,讨论享有至高无上的地位,讨论是课堂教学的主旋律;而中国教师喜欢讲课,培养整齐划一的高材生。现在,中美联系比以往更加紧密,中国人学英语,玩保龄球,吃
最新回复
(
0
)