Question

In which of the configuration of a transistor, the power gain is highest?
A) Common base
B) Common emitter
C) Common collector
D) Same in all the three.

Answer 1

Hint:In common emitter configuration, input is applied between base and emitter and output is taken from the collector and emitter. Here, the emitter of the transistor is common to both input and output circuits and hence the name common emitter connection.

Complete step by step answer:
In a transistor there are three terminals namely emitter, base and collector. To construct a transistor circuit, we require four terminals; two for the input and two for the output. This difficulty can be solved by making one terminal of the transistor common to both input and output terminals. The input is fed between this common terminal and one of the two terminals. The output is produced between the common terminal and the remaining terminal. Accordingly; a transistor can be connected in a circuit in the following three configurations.
Common base (CB) configuration.
Common emitter (CE) configuration.
Common collector (CC) configuration.
The CE configuration is the most widely used configuration and n-p-n transistors are the most commonly used transistors.

Common emitter transistors are used most widely, because a common emitter transistor amplifier provides high current gain, high voltage gain and high power gain. This type of transistor gives for a small change in input there is small change in output. The output voltage is 180 degree out of phase with the input voltage.

therefore Correct option is (B)

Note:In CE mode, collector current $I_c$ is the output current and base current $I_B$ is the input current. The current gain depends on whether the current flowing is dc or ac.
An amplifier is a device that increases the amplitude of the ac signal. The process of increasing the amplitude of an ac signal is called amplification.
Power gain is the ratio of output power to its input power.