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
68
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.
What discovery made live voice broadcasting become a reality?
选项
A、Carbon filament.
B、Diode.
C、Triode.
D、Wireless telegraph.
答案
C
解析
根据题干中的关键词live voice broadcasting定位到文章第四段最后一句:It could amplify a signal to make live voice broadcasting possible, and was quickly added to Marconi’s wireless telegraph to produce the radio。它可以增强信号,使在线声音播放成为可能,并且很快应用到马可尼的无线电报中,产生了无线电广播。而这一句中的it是指上一句中提到的triode,所以本题的正确答案是C)。
转载请注明原文地址:https://kaotiyun.com/show/PtN7777K
0
大学英语四级
相关试题推荐
Researchersfoundfamilyinfluenceddelinquency.Attachmentandinvolvementwereboth【S1】______relatedtodelinquency.Children
A、FoodAdditives.B、Cancer-relatedlabels.C、Food-relateddiseases.D、BadEffectsofFoodonHealth.D
PsychologistGeorgeSpilichandcolleaguesatWashingtonCollegeinChestertown,Maryland,decidedtofindoutwhether,asmany
A、Sincethefall.B、Sincethesummer.C、Forayearandahalf.D、Forthreeyears.C时间题。从男子的第二句对话“Afterayearandahalf?”中可以知道女
FifteenyearsagoMasco,asmallfamilyfirm,suddenlygrewfast.Asitgrew,themanagementrealizedthatchangeswereneeded.
FifteenyearsagoMasco,asmallfamilyfirm,suddenlygrewfast.Asitgrew,themanagementrealizedthatchangeswereneeded.
A、Sheisbuyingaear.B、Sheisinsuringhercar.C、Sheisrentingacar.D、Sheisputtinggasintothetank.C信息词International
A、At10o’clock.B、At12o’clock.C、At14:30.D、Itisnotmentioned.A根据女士说的话Iwasherebytenthismorning可得知她的上班时间。
Ifalltofinishthatproject.I__________(本该把时间和精力集中在工作上).
EvenifIhadknownheraddress,______(我也可能没有时间写信给她).
随机试题
直接滴定法测还原糖时,滴定至终点,蓝色消失呈浅黄色,稍放置后指示剂被氧化会重新变成蓝色,此时需继续滴定。
历史上有些经济上比较落后的国家在某些思想领域超过了经济上比较发达的国家,这一现象说明()。
A.腰阳关B.大杼C.膈俞D.长强上述腧穴中,属于督脉经的络穴是
A.感觉性失语B.运动性失语C.混合性失语D.命名性失语E.构音不良
乙因病需要换肾.其兄甲的肾脏刚好配型成功,甲乙父母和甲均同意由甲捐肾。因甲是精神病人,医院拒绝办理。后甲意外死亡,甲乙父母决定将甲的肾脏捐献给乙。下列哪一表述是正确的?(2011年卷三第2题)
汉代曾发生这样一件事情:齐太仓令获罪当处墨刑,其女缇萦上书请求将自己没为官奴,替父赎罪。这一事件导致了下列哪一项法律制度改革?(2005年司法考试试卷一第17题)
某二级公路路堤边坡基本稳定,坡面只有轻微冲刷,最适合于此处的坡面防护措施是()。
根据以下资料回答下列问题。中学课本和小学课本的种数和约比教学用书多几倍?()
“九一八”事变以来,使日本对中国的侵略计划步步得逞的原因有
Becauseofthelargeexportof______,NewZealandiscalled"theworld’sbiggestfarm".
最新回复
(
0
)