Transistor

In recent years, the transistor has replaced the Billy thermionic valves in most, if not all, electronic applications. It is used as amplifier in communication, control , and computer systems. Transistors are far smaller than valves. They have no filament, and by that they do not need any heating power. They can be operated in any position, and under any condition. Basically, transistors are mechanically rugged, their life span is very long, and they can do some jobs better than valve devices. the responses of transistors are very fast, e.g. transistorized radio, t.v etc. Start working immediately after switching them on, unlike valve radios.

    The transistor is a solid state device consisting of a tiny piece of semi conductor, usually germanium or silicon, to which three or more electrical connections are made. The basic components of the transistor are comparable to those of a triode vacuum tube and include the emitter, which corresponds to the heated cathode of the triode tube as the source of electrons. 

In contrasts to the valve devices which make use of the flow of the electrons through either a vacuum or gas, a transistor relies or depends mostly in the movement of charge carriers through solid substances which are semi conductors to their operations.  

   As at now,  there are many varieties of semi conductors, but the two most frequently used in electronics and transistor manufacture are germanium and silicon semi conductor materials. These semi conductors can be made to be of N type, I.e. having electrons a the charge carrier, or they can be of P type, I.e. having protons as the charge carrier. When N type and P type semi conductors are placed side by side, they will form a P-N junction which may be seen as being similar to the anode and cathode of the conventional diode valve as formerly discussed.