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An electron gun is an assembly of electronic parts inside a television or computer cathode ray tube (CRT) which produce an electron beam to light up a phosphorous coating on the inside glass surface of a TV or monitor. The electron gun is the heart of the CRT found in televisions and computer monitors. It is comprised of several parts, including an electrode positioned inside of the CRT that produces a highly focused beam of accelerated electrons. The beam creates a visible image on the inside of the large glass screen. Modern flat panel TVs and computer monitor do not use an electron gun.
The element, or filament, in an electron gun is heated and maintained at a high, negative voltage. The TV or computer tube screen also maintains a high charge, but this charge is the opposite of the charge in the electron gun. When the filament reaches a certain temperature, the electrons have enough energy to escape the negative voltage and fly, or shoot, toward the inside of the screen, illuminating the phosphors that coat the glass. The simplest example of this kind of phenomenon is the electrically charged particles in the solar winds that hit the earth's atmosphere and cause the Aurora Borealis, or Northern Lights, to glow in the sky.
The electron gun fires a focused beam of electrons toward the glass of the CRT. This beam must hit every pixel on the screen about 70 times every second. The surface of the inside of the screen is coated with a phosphorescent material that glows in a specific color when hit with these electrons. The beam must hit a precise point with just the right frequency of electrons to produce a particular color on the screen. A mask ensures a direct hit on a specific point and provides a crisp, clear pixel on the screen.
The phosphors on the inside of the screen only stay lit for a fraction of a second, so the electron beam must continually refresh them to keep them bright. The electron gun starts at the top left side of the screen and sprays a beam of focused electrons toward the screen from left to right. On a typical 800 x 600 resolution screen, the electron gun must beam electrons on 800 pixels per row across 600 rows 75 times per second or more. Magnetic fields help to guide the electrons to the pixels more accurately. When these electrons hit the inside of the TV screen, they become light energy and leave the screen as light.