Television shows still pictures. The pictures appear to move because they are shown one after the other at high speed. To give this impression there must be thirty pictures per second.
Color television is more complicated. There are three electron beams each of which carries the signal for one of the colors, red, blue, and green. The screen of the picture tube is coated with 1-1/4 million tiny dots of phosphor, arranged in groups of three. A phosphor is a substance that emits light when an electron beam falls on it; each of the three phosphors used emits only one of the three colors red, blue, and green. So the blue phosphor emits blue light when the electron beam carrying the blue signal falls on it, and so on. These three colors can be combined in different proportions to give all the other colors of the original televised scene.
Television can be either broad cast, as it is for entertainment, or it can be transmitted by wire. This is called closed-circuit television. Closed-circuit television is used for a number of purposes. For example, it can be used in hospitals to enable students to see the details of an operation.
Color television is more complicated. There are three electron beams each of which carries the signal for one of the colors, red, blue, and green. The screen of the picture tube is coated with 1-1/4 million tiny dots of phosphor, arranged in groups of three. A phosphor is a substance that emits light when an electron beam falls on it; each of the three phosphors used emits only one of the three colors red, blue, and green. So the blue phosphor emits blue light when the electron beam carrying the blue signal falls on it, and so on. These three colors can be combined in different proportions to give all the other colors of the original televised scene.
Television can be either broad cast, as it is for entertainment, or it can be transmitted by wire. This is called closed-circuit television. Closed-circuit television is used for a number of purposes. For example, it can be used in hospitals to enable students to see the details of an operation.
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