I. Определите, является ли утверждение:

1. Internal-combustion engines don’t receive their input energy from a natural source.

A) ложным

B) в тексте нет информации

C) истинным

2. First machines are reported to appear in ancient times.

A) в тексте нет информации

B) ложным

C) истинным

3. After the advent to steam engine material goods were produced by power-driven machines.

A) в тексте нет информации

B) ложным

C) истинным

4. The lever, the wheel and axle are prime movers.

A) истинным

B) в тексте нет информации

C) ложным

II. Укажите, какой части текста (1, 2, 3, 4) соответствует следующая информация:

1. Various natural sources of input energy for machines.

A) 3

B) 4

C) 2

D) 1

2. The main purpose of any machine.

A) 1

B) 4

C) 2

D) 3

III. Выберете правильный вариант ответа на вопрос:

What may the input energy of prime movers be based on?

A) It may be based on the transformation of energy or modification of forces and motions.

B) It may be based on the work of calculating machines and typewriters.

C) It may be based on such complex mechanical systems as the modern automobile.

D) It may be based on manually operated instruments of all kinds.

IV. Определите основную идею текста:

A) General classification of machines and the main principles of their operation.

B) Combination of different categories of machines in one unit.

C) Prime movers capable of rotating shafts of generators, pumps, or compressors.

D) Generators as inputs to electric, hydraulic, or air motors.

Optical fibers

1. Optical fibers, used in modern optical communication systems are an example for the application of an advanced ceramic material. They are made of extremely high-purity silica, which must be free of even extremely small levels of impurities and other defects that would absorb, scatter or weaken a light beam. Sophisticated processing has been developed to produce fibers that meet the rigorous restrictions required for this application, but such processing is costly.

2. Optical fibers started to replace some uses of copper cables in the 1970s, e.g. in telecommunications and cable TV. In these applications they are the preferred material, because the fibers carry signals more efficiently than copper cable and with a much higher bandwidth, which means that they can carry more channels of information over longer distances. For optical fibers, the longer transmission distances require fewer expensive repeaters.

3. Also, copper cable uses more electrical power to transport the signals. In addition, optical fiber cables are much lighter and thinner (about 120 micrometers in diameter) than copper cables with the same bandwidth so that they take up less space in underground cabling ducts. It is difficult to steal information from optical fibers and they resist electromagnetic interference, e.g. from radio signals or lightning. Optical fibers don’t ignite so they can be used safely in flammable atmospheres, e.g. in petrochemical plants.

4. Due to their required properties, optical fibers are more expensive per meter than copper. In addition, they can’t be spliced as easily as copper cable, thus special training is required to handle the expensive splicing and measurement equipment.