Depletion areas Depletion areas P P N Collector Collector Emitter Emitter Base Base N N P Collector Collector Emitter Emitter Base Base Typical Transistors  PNP Transistor  NPN Transistor  Symbols for transistors used in an electronic circuit diagram Collector-base depletion area Emitter-base depletion area B C E I$_{B}$ I$_{B}$ I$_{C}$ I$_{E }$= I$_{B }$+ I$_{C}$ I$_{E }$= I$_{B }$+ I$_{C}$ I$_{C}$ E$_{B}$ E$_{C}$ − + − + P N P E$_{B}$ E$_{C}$ − + − + I$_{B}$ I$_{C}$ I$_{C}$ 11-12 Figure 11-27.  The effect of applying a small voltage to bias the emitter-base junction of a transistor (top). A circuit diagram for this  same transistor (bottom).  Figure 11-26.  Typical transistors, diagrams of a PNP and NPN transistor, and the symbol for those transistors when depicted in an  electronic circuit diagram. 