Electric charges are divided into positive charge-proton and negative charge-electron.
The electrons are constantly attarcted to the protons within its vicinity to form an atom.This force of pulling them togehther is the electric force.Hence the science of electronics is the study of the behavior of electrons under set conditions.
When two poles (eletrodes) with different voltages one positive,the other negative are placed close to each other,free electrons from the negative electrode will follow towards the positive electrode.The phenomenon just described is not possible in open air,but it will be possible within a vacuum glass tube where the electrons can follow unobstructed.
Here the positive eletrode is given the name Anode (or plate as sometimes called),the negative electrode is called the Cathode.
The diagram on the right shows more than 2 legs,what are the extra legs? They are the heaters' supply leads. The number of free electrons emitted from the cathode will increase many folds when it is heated.More electrons,more electric current,so heaters are introduced.
We have just learned the principle behind the operations of the most basic vacuum tube the Diode.
Diodes were used principally in rectifiers of alternative current into direct current.
We will next describe a far more important device the Triode in another post.
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