An electron gun is a component that produces an electron stream that has a precise kinetic energy, being used in all TVs and monitors which use cathode ray tube technology.
Basically it is formed of two parts: one is a metal filament, which is heated to create a stream of electrons (a thermionic emission), with a small initial energy. Then, the second part is an electric field, which accelerates them to reach the anode.
The CRT is made up of three electron guns, each one producing a different stream of electrons, which make either red, green or blue phosphor to light up, each pixel of the screen being made by combining these three colours.
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