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Форум » Учеба и все что с ней связано » Важный учебный форум » Методические пособия (Методические пособия - пособите товарищи!)
Методические пособия
QuardellarilДата: Вторник, 14.11.2006, 15:57 | Сообщение # 1
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Кто-нибудь пособите! Выложите методичку за третий семестр по физике в файловый архив! Или притащите мне на каком-либо носителе! Или дайте на денек реальную методичку! cry

~ Главная ошибка - не исправлять своих прошлых ошибок. ~
HozerДата: Суббота, 10.03.2007, 20:26 | Сообщение # 2
ОЧЕНЬ важный студент
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2 - ая группа по английскому - текст на пересказ 1
What is Fiber Optics?
In 1880, four years after he invented the telephone, Alexander Graham Bell tested another device. He called it the photophone.
“Photo and “Phone” come from the Greek words for “light” and “sound”. Bell’s telephone used pulses of electricity traveling over copper wires to carry sound. But the photophone used a beam of sunlight traveling through air carry the human voice one to another.
Bell was very enthusiastic about the photophone. He wrote to his father, “I have heard a ray of sun laugh and cough and sing!”
However, the new invention did not prove to be very practical. Sunlight was only available during the daytime. And even then, bad weather such as fog, rain, or snow blocked the beam of light.
In spire of these problems, throughout his life, Alexander Graham Bell thought the photophone was his most promising idea. He felt certain that someday people would use beams of light to talk to each other.
For nearly one hundred years, scientists like Bell dreamed of using light to communicate. They knew that more light waves could be transmitted in one second than electricity flowing in copper wires.
Not until the 1960s and 1970s did two inventions make the dream possible. During this time, scientists invented lasers. Lasers are powerful sources of a special kind of light. Other researchers developed optical fibers.
An optical fiber is a flexible thread of very clean glass – thinner than a cat’s whisker and up to six miles long. Laser light can pass through the length of an optical fiber and still stay bright. Because optical fibers can serve as pipelines for light, they also are called light guides.
In the mid 1970s, these inventions were teamed together. Now pulses of light flash through optical fibers carrying information and messages over great distances. This important new technology is called fiber optics.
Glass fibers are replacing copper wires for many reasons. The fiber are not as expensive for telephone companies to buy and install. They weigh a lot less than copper wires – making them easier for workers to handle. A single four – and – one – half – pound spool of optical fiber can carry the same number of messages as two hundred reels of copper wire than over sixteen thousand pounds!
Optical fibers also take much less space than copper wires. This is very important in crowded cities where building, overloaded telephone cables have little room for additional lines. Optical fibers can help unsnarl this traffic jam.
The fibers are better, too, because light is not affected by nearly electrical generators, motors, power lines, or lightning storms. These often are the cause of noisy static on telephone or information errors in computer systems connected by copper wires.
As electrical signals pass through copper wires, they become weekend.
Devices called repeaters are used to strengthen the electrical signals about every mile along each line. In a fiber optic system, repeaters are needed only every six miles or so to boost the signals. And experiments have shown that this distance can be stretched many more miles. This means that installation costs for a fiber optic system are less now and can be cut further in the future.
However, the most important reason for using glass fibers is that they can carry much more information than the copper wires. A single pair of threadlike glass fibers can transmit thousands of telephone calls at once. A cable as thick as your arm and containing 256 pairs of copper wires would be needed to handle the same number of conversations.
Pairs of fiber are used for two-way communication. One fiber carries your voice to the listener at the other end of line. The other member of the pair transmits the other person’s reply to you.
Optical fibers are less expensive, easier to install, and more dependable than copper wires. With light from a laser, they can transmit thousands of times more information than electricity in copper wires. The new technology of fiber optics is a better and faster way to communicate.
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