An electron gun (also called electron emitter) is an electrical component in some vacuum tubes that produces a narrow, collimated electron beam that has a precise kinetic energy. The largest use is in cathode ray tubes (CRTs), used in older television sets, computer displays, and oscilloscopes. They are also used in microwave linear beam vacuum tubes such as klystrons, inductive output tubes, travelling wave tubes, and gyrotrons, as well as in scientific instruments such as electron microscopes and particle accelerators. Black-and-white, often abbreviated B/W or B&W, is a term referring to a number of monochrome forms in visual arts. Television programming was first broadcast in black-and-white. Colour television is part of the history of television, the technology of television and practices associated with television's transmission of moving images in colour video that came later. A monochrome picture tube has one electron gun and a continuous phosphor coating that produces a picture in black and white. A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. For colour picture tube the screen is formed of three different phosphors and there are three electron beams, one for each colour phosphor. The three colours-red, green and blue produced by three phosphors combine to produce different colours.
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