Vacuum tube is widely used in our daily life. In order to have a deep understanding of it, Easybom has done a detailed study on the development process of vacuum tube. People working in the electronic industry and interested in electronics can learn from the following content summarized Easybom.
The flow of current and electrons
Of course, the vacuum tube has not experimented with several metal plates installed in a vacuum glass bottle for no reason. The development of vacuum tube is related to the invention of king Edison.
There is a small question: Do the current in circuit analysis and electrons share the same flow direction? The answer is no, the direction of current and electron flow are exactly opposite. In the past, scientists could not observe the direction of electron flow, so they set a certain pole of the battery as the positive electrode and its voltage was a positive voltage, and the current flowed from the positive electrode to the negative electrode to form a closed loop. Because they unified statements and practices, there has been no conflict for many years. But in modern time, scientists used more sophisticated equipment to observe it, and then they overturned the previous statement. “It comes to the conclusion that the negative end of the battery is the place where the electrons flow out from!”
As a user, it is unnecessary for us to make clear which statement is true and we only need to act according to the conclusion of the scientists. After the bulb invented by Edison, he found that the filament of the light bulb he produced always burned from the positive end, so he conducted an experiment. He added a small metal plate into the bulb, then connected the metal plate to the electric meter after lighting, and applied positive voltages and negative voltage respectively, and finally observed the current situation.
With respect to the science at that time, metal plates in a vacuum without connection could not generate current. But something strange happened. Edison discovered that a certain substance (in fact, electrons) would pass through the metal plate and jump from the negative pole of the battery to the positive pole. This discovery provoked greater experimental motivation. This phenomenon is called the “Edison effect”. This is also the first time scientists have questioned the direction of current flow and the phenomenon of free electrons flowing in space.
The birth of the vacuum tube
The reason why metals can conduct electricity is that they have more free electrons, which facilitate the flow of electrons. Therefore, electronic materials must be made of materials with good conductivity. Electrons have another characteristic. Negatively charged electrons are easily attracted by positive voltage, which is the so-called repulsion of homosexual and heterosexual attraction. We can also know from the Edison effect that when a metal substance is heated, the free electrons active in the periphery of protons are prone to dissociation and high temperature leads to enhanced electron activity. At this time, if there is a positive voltage in the space to strongly attract them, the dissociated electrons will flow in space. Based on the knowledge that was already understood at that time, J.A.Fleming produced the first diode vacuum tube in 1904. DeForest Lee improved the diode and produced the first triode in 1907. Since the successful development of the triode, the application of the vacuum tube has begun to be realized.