Metal can conduct electricity because there are many free electrons in metal, which facilitates the mutual flow of electrons, so electronic materials must be made of materials with good conductivity. Electrons have another feature. Electrons with negative charges are easily attracted by positive voltages, so-called like charges repel and opposite charges attract.
The Edison effect also shows that when a metal substance is heated, the active free electrons around the proton are easily dissociated, and the high temperature leads to the enhancement of electron activity. At this time, if there is a strong attraction of positive voltage in space, dissociated electrons will flow in space.
Based on this understanding, J.A. Fleming made the first diode vacuum tube in 1904, and deforest improved the diode and made the first triode in 1907. Since the successful development of triode, the application of vacuum tube has been realized, and the vacuum tube has developed rapidly since then.
Extended data:
A vacuum tube has three basic poles. The first is the cathode (denoted by K): the cathode is of course the negative electrode, where the electron flow is released. It can be a metal plate or the filament itself. When the filament heats the metal plate, electrons will be released and dispersed in a small vacuum glass bottle.
The second pole is the "plate" (denoted by P), which is basically the outermost metal plate of the vacuum tube. When the eyes see the outermost dark gray or black metal plate of the vacuum tube, it is usually this plate. The screen electrode is connected with a positive voltage, which is responsible for attracting electrons emitted by the cathode (using the principle of opposites attracting) as the end point of free travel of electrons.
Roof of the world is a "case" (denoted by G). Structurally, it is like a thin coil, like a fence, fixed between the cathode and the screen. The electron flow must reach the screen through the grid, and the voltage between the grids can control the electron flow. It acts like a faucet, with the functions of circulation and blockage.
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