In a transistor, comparing the doping of emitter, base and collector, the part which is heavily doped and that which is lightly doped are respectively

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In a transistor, the emitter is heavily doped so that it can inject a large number of charge carriers into the base. The base is lightly doped and kept very thin to reduce the recombination of charge carriers. The collector is moderately doped and is the largest in size to dissipate heat. Thus, the heavily doped part is the emitter and the lightly doped part is the base. Answer: emitter and base