Question

Differentiate between NPN and PNP transistors.

Answer 1

Hint: When the anodes of the two diodes are fused, the transistor is called an NPN transistor. When the cathodes of the two diodes are fused, the transistor is called a PNP transistor.

Complete step by step answer:
A transistor is a semiconductor device, which is formed by fusing two junction diodes. When the anodes of the two diodes are fused, the transistor is called an NPN transistor. When the cathodes of the two diodes are fused, the transistor is called a PNP transistor.
A transistor consists of three parts – a collector, an emitter and a base. The middle part is base.
Let us discuss the differences between a PNP and a NPN transistor.
(i) The first difference is that a PNP transistor consists of two p-type diodes with a n-type diode in between them, whereas a NPN transistor consists of two n-type diodes with a p-type diode in between them.
(ii) In a PNP transistor, the current flows from the emitter to the collector. Whereas in a NPN transistor, the current flows from collector to emitter.
(iii) In PNP transistors, the majority charge carriers are holes. Whereas the majority charge carriers in a NPN transistor are electrons.

Note: Note that holes here does not mean literal holes inside the transistors. Holes are the positive charge developed due the vacancy of electrons.
Note that the current in NPN transistors is due to the movement of electrons and the current in PNP transistors is due to the movement of holes.