The cathode ray tube or CRT was invented by Karl Ferdinand Braun. It was the most common type of display for many years. It was used in almost all computer monitors and televisions until LCD and plasma screens started being used.
A cathode ray tube is an electron gun. The cathode is an electrode (a metal that can send out electrons when heated). The cathode is inside a glass tube. Also inside the glass tube is an anode that attracts electrons. This is used to pull the electrons toward the front of the glass tube, so the electrons shoot out in one direction, like a ray gun. To better control the direction of the electrons, the air is taken out of the tube, making a vacuum.
The electrons hit the front of the tube, where a phosphor screen is. The electrons make the phosphor light up. The electrons can be aimed by creating a magnetic field.

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