Transistor working: Physics
A transistor consists of a single crystal of germanium or Silicon, which is grown in such a way, that it has three regions.
Transistors can be divided into two types. P-n-p transistors, and n-p-n transistors. In n-p-n type transistors, the central region is p type, which is sandwiched between two n type regions.
In p-n-p type transistors, the n type central region, is sandwiched between two P type regions. The central region is known as base, and the other two regions are called emitter and collector.
Usually the base is very thin, of the order of 10 micrometer. The collector is comparatively larger than the emitter. The emitter has greater concentration of impurity as compared to the collector. A transistor is a combination of two back to back p-n junctions: emitter-base junction and collector-base junction.