Прочитайте текст и выполните задания Digital electronics 1. Computers understand only two numbers 0 ...: ответ на тест 860654 - Английский язык

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Digital electronics
1. Computers understand only two numbers, 0 and 1, and do all their arithmetic operations in this binary mode. Many electrical and electronic devices have two states: they are either off or on. Because computers have been a major application for integrated circuits from their beginning, digital integrated circuits have become commonplace. It has thus become easy to design electronic systems that use digital language to control their functions and to communicate with other systems.
2. A major advantage in using digital methods is that the accuracy of a stream of digital signals can be verified, and, if necessary, errors can be corrected. An example is the sound from a phonograph record, which always contains some extraneous sound from the surface of the recording groove even when the record is new. Contrast this with the sound from a digital compact disc recording. The disc and the player contain error-correcting features that remove any incorrect pulses (perhaps arising from dust on the disc) from the information as it is read from the disc.
3. As electronic systems become more complex, it is essential that errors produced by noise be removed; otherwise, the systems may malfunction. Many electronic systems are required to operate in electrically noisy environments, such as in an automobile. The only practical way to assure immunity from noise is to make such a system operate digitally.
4. Any electrical system generates some noise, and all electronic systems are to some degree susceptible to disturbance from noise. The noise may be conducted along wires connected to the system, or it may be radiated through the air. Care is necessary in the design of systems to limit the amount of noise that is generated and to shield the system properly to protect it from external noise sources.
 (Encyclopedia Britannica)
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What protects electronic systems from malfunctioning?

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Digital electronics
1. Computers understand only two numbers, 0 and 1, and do all their arithmetic operations in this binary mode. Many electrical and electronic devices have two states: they are either off or on. Because computers have been a major application for integrated circuits from their beginning, digital integrated circuits have become commonplace. It has thus become easy to design electronic systems that use digital language to control their functions and to communicate with other systems.
2. A major advantage in using digital methods is that the accuracy of a stream of digital signals can be verified, and, if necessary, errors can be corrected. An example is the sound from a phonograph record, which always contains some extraneous sound from the surface of the recording groove even when the record is new. Contrast this with the sound from a digital compact disc recording. The disc and the player contain error-correcting features that remove any incorrect pulses (perhaps arising from dust on the disc) from the information as it is read from the disc.
3. As electronic systems become more complex, it is essential that errors produced by noise be removed; otherwise, the systems may malfunction. Many electronic systems are required to operate in electrically noisy environments, such as in an automobile. The only practical way to assure immunity from noise is to make such a system operate digitally.
4. Any electrical system generates some noise, and all electronic systems are to some degree susceptible to disturbance from noise. The noise may be conducted along wires connected to the system, or it may be radiated through the air. Care is necessary in the design of systems to limit the amount of noise that is generated and to shield the system properly to protect it from external noise sources.
 (Encyclopedia Britannica)
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Flicker
1. The first requirement to be met in image analysis is that the reproduced picture shall not flicker, since flicker induces severe visual fatigue. Flicker becomes more evident as the brightness of the picture increases. If flicker is to be unobjectionable at brightness suitable for home viewing during daylight as well as evening hours, the successive illuminations of the picture screen should occur no fewer than 50 times per second. This is approximately twice the rate of picture repetition needed for smooth reproduction of motion. To avoid flicker, therefore, twice as much channel space is needed as would suffice to depict motion.
2. The same disparity occurs in motion picture practice, in which satisfactory performance with respect to flicker requires twice as much film as is necessary for smooth simulation of motion. A way around this difficulty has been found, in motion pictures as well as in television, by projecting each picture twice. In motion pictures, the projector interposes a shutter briefly between film and lens while a single frame of the film is being projected.
3. In television, each image is analyzed and synthesized in two sets of spaced lines, one of which fits successively within the spaces of the other. Thus the picture area is illuminated twice during each complete picture transmission, although each line in the image is present only once during that time. This technique is feasible because the eye is comparatively insensitive to flicker when the variation of light is confined to a small part of the field of view.  
4. It is thus possible to avoid flicker and simulate rapid motion by a picture rate of about 25 per second, with two screen illuminations per picture. The precise value of the picture-repetition rate used in a given region has been chosen by reference to the electric power frequency that predominates in the region.  
 (Encyclopedia Britannica)
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Flicker can do much harm to human health.  

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Colour television
1. After World War II, the Columbia Broadcasting System (CBS) began demonstrating its own sequential colour system, designed by Peter Goldmark. Combining cathode-ray tubes with spinning wheels of red, blue, and green filters, it was impressive enough that The Wall Street Journal had “little doubt that color television had reached the perfection of black and white.” Thus began a long battle between CBS and RCA (Radio Corporation of America) to decide the future of colour television which resulted in abandoning the broadcasts a few months later.
2. Then, in June 1951, RCA proudly unveiled their new system. The design used dichroic mirrors to separate the blue, red, and green components of the original image and focus each component on its own monochrome camera tube. The RCA colour system was compatible with existing black-and-white sets. It managed this by converting the three colour signals into two: the total brightness, or luminance, signal and a complex second signal containing the colour information.  
3. In 1952 the National Television Systems Committee (NTSC) was reformed, this time with the purpose of creating an “industry color system.” The NTSC system that was demonstrated to the press in August 1952 and that would serve into the 21st century was virtually the RCA system. It was not until the 1960s that colour television became profitable.
4. In 1960 Japan adopted the NTSC colour standard. In Europe, two different systems came into prominence over the following decade: in Germany Walter Bruch developed the PAL (phase alternation line) system, and in France Henri de France developed SECAM (système électronique couleur avec mémoire (successive colour with memory)). Both were basically the NTSC system, with some subtle modifications.  These are still the standards of colour television today, despite preparations for a digital future.
(Encyclopedia Britannica)
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Present television systems being used in Europe appeared later than NTSC system.

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Digital electronics
1. Computers understand only two numbers, 0 and 1, and do all their arithmetic operations in this binary mode. Many electrical and electronic devices have two states: they are either off or on. Because computers have been a major application for integrated circuits from their beginning, digital integrated circuits have become commonplace. It has thus become easy to design electronic systems that use digital language to control their functions and to communicate with other systems.
2. A major advantage in using digital methods is that the accuracy of a stream of digital signals can be verified, and, if necessary, errors can be corrected. An example is the sound from a phonograph record, which always contains some extraneous sound from the surface of the recording groove even when the record is new. Contrast this with the sound from a digital compact disc recording. The disc and the player contain error-correcting features that remove any incorrect pulses (perhaps arising from dust on the disc) from the information as it is read from the disc.
3. As electronic systems become more complex, it is essential that errors produced by noise be removed; otherwise, the systems may malfunction. Many electronic systems are required to operate in electrically noisy environments, such as in an automobile. The only practical way to assure immunity from noise is to make such a system operate digitally.
4. Any electrical system generates some noise, and all electronic systems are to some degree susceptible to disturbance from noise. The noise may be conducted along wires connected to the system, or it may be radiated through the air. Care is necessary in the design of systems to limit the amount of noise that is generated and to shield the system properly to protect it from external noise sources.
 (Encyclopedia Britannica)
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Flicker
1. The first requirement to be met in image analysis is that the reproduced picture shall not flicker, since flicker induces severe visual fatigue. Flicker becomes more evident as the brightness of the picture increases. If flicker is to be unobjectionable at brightness suitable for home viewing during daylight as well as evening hours, the successive illuminations of the picture screen should occur no fewer than 50 times per second. This is approximately twice the rate of picture repetition needed for smooth reproduction of motion. To avoid flicker, therefore, twice as much channel space is needed as would suffice to depict motion.
2. The same disparity occurs in motion picture practice, in which satisfactory performance with respect to flicker requires twice as much film as is necessary for smooth simulation of motion. A way around this difficulty has been found, in motion pictures as well as in television, by projecting each picture twice. In motion pictures, the projector interposes a shutter briefly between film and lens while a single frame of the film is being projected.
3. In television, each image is analyzed and synthesized in two sets of spaced lines, one of which fits successively within the spaces of the other. Thus the picture area is illuminated twice during each complete picture transmission, although each line in the image is present only once during that time. This technique is feasible because the eye is comparatively insensitive to flicker when the variation of light is confined to a small part of the field of view.  
4. It is thus possible to avoid flicker and simulate rapid motion by a picture rate of about 25 per second, with two screen illuminations per picture. The precise value of the picture-repetition rate used in a given region has been chosen by reference to the electric power frequency that predominates in the region.  
 (Encyclopedia Britannica)
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