Question

In a transistor,

Options

•  the emitter has the least concentration of impurity

• the collector has the least concentration of impurity

• the base has the least concentration of impurity

• all the three regions have equal concentrations of impurity.

Answer 1

the base has the least concentration of impurity

When the emitter of a transistor is forward biassed, the majority carriers move from the emitter to the collector through the base. As the base is thin and lightly doped, only small amount of a combination of electrons and holes takes place, leading to weak base current. This makes the collector current equal to the emitter current.
If we make any other choice for least concentration of impurity, we will have a low value of collector current. Thus, the purpose of a transistor will not be fulfilled.