We know, the flow of electrons is electric current. Electrons are said to be negative charge carriers. In a molecular structure, if there is a vacancy for an electron, it is called hole . When an electron from somewhere in the structure fills-up this hole, a new hole will be created where the electron has just left. Hence a hole can move opposite to the electron . So the holes are said to be positive charge carriers. In a germanium crystal, arsenic is infused. We get electron rich material called N type (negative) material. When boron is added to germanium, we get holes surplus P type (positive) substance. A thin P type material is sandwiched between two N type material. Now a transistor is made. These three pieces NPN are respectively called emitter, base, and collector. By connecting negative of the battery to the emitter(N) and positive to the collector(N), the electrons can be pushed from emitter and pulled at the colle
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