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A cathode-ray tube is a display device used in television sets and computer monitors. It is a kind of vacuum tube which contains one or more electron guns, electrostatic deflection plates and a phosphor target which is located at the back of the glass screen. A cathode for which the CRT got its name is a positive terminal at which electrons may enter.
In a computer monitor or in a television set, the entire front of the tube is being scanned systematically and rapidly in a fixed pattern which is called a raster. Images and color are produced by shooting and controlling the electron beams representing each additive color light (red, blue and green) using the video signal as the reference.
Modern CRT monitors use magnetic deflection to bend the electron beams. This is done by varying the magnetic field generated by coils which is driven by electronic circuits located along the neck of the tube.
A cathode ray tube is a specialized vacuum tube where images can be created by shooting electrons beams at the phosphorescent surface. The CRT also known as the picture tube was the only choice for a display device up until the less bulky and less power hungry LCD was invented. They usually employ magnetic deflection for changing the orientation of the electron beams but other types use electrostatic deflection. These are usually used in oscilloscopes as magnetic deflection which would lessen the inductive reactance of the magnetic coils and limit the frequency response of the oscilloscope.
The brightness, color and persistence of the illumination can be varied by using different kinds of phosphor. This is especially useful for making CRTs for different applications.