Question

One way in which the operation of a n-p-n transistor differs from that of a p-n-p is that,
A. The emitter junction injects minority carriers into the base region of the p-n-p
B. The emitter injects holes into the base of the p-n-p and electrons into the base region of n-p-n
C. The emitter injects holes into the base of n-p- n
D. The emitter junction is reversed biased in n-p-n

Answer 1

Hint: Transistor is a three terminal device. The three terminals of a transistor are emitter, base and collector. Now these three junctions are made from semiconductors and the semiconductor used is not intrinsic but doped, so, it can be either n type or the p type. Then we can have n-p-n transistors or p-n-p transistors. Depending upon the biasing of the transistor we came to know whether majority charge carriers or the minority charge carriers are playing the dominant role.

Complete answer:
The given transistor is n-p-n type and thus the emitter base junction is forward biased and collector base junction is reverse biased. When connected to an external source then an emitter which has electrons as majority charge carriers, injects holes into the base and collector injects electrons into the base. While in the case of a p-n-p transistor, the case is just exactly opposite.

Hence, the correct option is B.

Note: The emitter is largest in size while the base is the smallest in size. The base size is determined by the doping. Also, the region between the emitter base junction and the collector base junction is separated by a region called the depletion region which is devoid of majority charge carriers and contains only minority charge carriers. One of the most important uses of n-p-n transistors is in the form of an amplifier.