Question

16. Which of the following does not accurately describe transistors?

A. Both NPN and PNP transistors consist of an emitter, base, and collector.

B. Both NPN and PNP transistors consist of P-type and N-type material.

C. Both NPN and PNP transistors operate in the same manner but with interchanged terminals and opposite directions of voltage and current.

D. Both NPN and PNP transistors consist of a base composed of an N-type material.


20.Combining which of the following substances with germanium will cause the germanium to emit free electrons?


A. Bismuth

B. Gallium

C. Aluminum

D. Indium

Answer 1

16. Answer is "D".

• There are two types of transistors as NPN type and PNP type. Both types have three parts as emitter (E), base (B), and collector (C).

• Both transistors have both N-type and P-type materials. In NPN transistors, base is a P-type material while PNP transistors have N-type material as the base.

• Both NPN and PNP transistors operate in the same manner but they have interchanged terminals and opposite directions of voltage and current.

20. Answer is "A - Bismuth".

In transistors, applying an impurity to a pure element to enhance the conductivity is called doping.

There are two types of doping as n-doping and p-doping.

n-doping -

Impurity has more valence electrons than the element of semiconductor. Example is silicon (4 valence electrons) with phosphorus (impurity with 5 valence electrons)

p-doping -

Impurity has less number of valence electrons than the element of semiconductor. Example is Si (4 valence electrons) with B (3 valence electron impurity).

Here, germanium has 6 valence electrons. To emit free electrons, germanium should combine with substance which has less number of valence electrons as bismuth (5 valence electrons).