Lesson 1 Video “The History of Communication”

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d) ________________________

For many decades cathode-ray tubes, or picture tubes, were used to display TV pictures. Such sets turn the video signal into beams of electrons. The picture tube is rectangular at the front where the screen is and narrow at the back.  Three electronic guns shoot electrons through the tube to the front of the screen, which is coated with phosphor. The beams paint thousands of dots on the screen to form the picture.

In the past decade LCDs and plasma displays have replaced the good old picture tube.  They are much lighter and thinner because they do not have a big tube in them.

LCD screens have liquid crystal layers that can be controlled by an electric current. Millions of pixels on these layers can be either switched on or off. The crystals pass through colour filters to produce millions of different colours.  

A plasma television is made up of two sheets of glass. Between them are millions of pixels filled with gas. Each pixel is coated with coloured phosphor, red, green and blue. When electricity passes through, it causes the coloured phosphor to produce light. (632 слова /1636 знаков)

По материалам http://www.english-online.at/media/television/television-technology.htm

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