Junction transistor. There are two principal types of transistors: the point-contact transistor and the junction transistor.
   A junction transistor consists of three principal sections and may be manufactured as one piece. In a n-p-n transistor the crystal consists of a section of n-type germanium, and another larger section of n-type germanium. One end of this transistor is called the emitter, the small p-type section is called the base, and the other end is called the collector. The collector is biased positive with respect to the base; hence there will normally be no current flow across the base-to-collector junction. The positive collector will draw the electrons away from the junction and the negative base will draw the holes away1 from the junction, and so there can be no transfer of holes or electrons at this point. Since the emitter is negative with respect to the base, the electrons will flow from the emitter to the base and the holes will move from the base to the emitter. This results in a substantial flow of electrons from the emitter to the base, and since the base is very thin, these electrons move across the base and into the positively charged collector.
   The result is that a substantial collector current will flow. This collector current will vary in accordance with the changes of the current flow across the emitter-to-base junction. Generally speaking, we may consider the operation of this transistor similar to that of a triode tube with the emitter representing the cathode,2 the base representing the control grid and the collector representing the plate.
   The advantages of a transistor are its very small size and weight, the fact that no power is necessary for heating it, and its comparatively rugged construction.