Question

A transistor has a base current of 1mA and emitter current 90 mA. The collector current will be
A. 90mA
B. 1mA
C. 89mA
D. 91mA

Answer 1

A transistor is a semiconductor device which is used as a component in many electrical circuits. To solve this question, obtain the relation between the collector current, bae current and the emitter current of a transistor. Then put the given values on the obtained expression to find the answer.

Complete step by step answer:
Given in the question that, the base current of the transistor is ${{I}_{b}}=1mA$
The emitter current of the transistor is, ${{I}_{e}}=90mA$
The relation between the collector current and the emitter current and the base current of a transistor can be mathematically expressed as,
$\begin{aligned} & {{I}_{e}}={{I}_{c}}+{{I}_{b}} \\\ & {{I}_{c}}={{I}_{e}}-{{I}_{b}} \\\ & {{I}_{c}}=90mA-1mA \\\ & {{I}_{c}}=89mA \\\ \end{aligned}$
So, the collector current of the transistor is 89 mA.
Hence, the correct answer is option C.

Additional Information
We have two types of transistors. NPN transistor and PNP transistor.
The emitter of a transistor transfers the large part of the majority charge carriers. The collector of the transistors collects the most of the majority charge carriers transferred by the emitter. The middle section of the transistor between the emitter and the collector is known as base. The emitter of the transistor is very highly doped, the collector is moderately doped and the base of the transistor is very lightly doped. The emitter base junction injects a large amount of charge carriers into the base because the emitter base junction is heavily doped and moderate in size.

Note:
A transistor can be used as an amplifier. An amplifier amplifies the input signal or current and amplifies it to a larger value of current. In hearing aids, loudspeakers etch we use transistors as an amplifier. Transistors can also work as switches in an electrical circuit.