Question

Explain the use of N-P-N transistors as an amplifier in common emitter mode under the following heads.

a. Labelled circuit diagram

b. Working

Answer 1

Hint: To solve this question we have to know about N-P-N transistors. We know that this is a semiconductor device that is generally used to amplify electronic signals or switch electrical power.

Complete step by step answer:

a) Labelled circuit diagram:

Here in this circuit we assumed that  $ {{I}_{b}} $  is the base current.

Again,  $ {{I}_{e}} $  is the emitter current.

 $ {{I}_{c}} $  is equal to collector current

X and Y are the batteries for the forward and the reverse biasing the junctions respectively. 

Now, we are considering that,  $ {{R}_{out}} $  is the load resistance. 

b) Working: we know that, in the positive half cycle of input alternating potential, the potential of base with respect to the emitter becomes more positive due to which the emitter current which is  $ {{I}_{c}} $  increases. So, we can say that with the increase of emitter current the collector current decreases. For this, the voltage across the load resistance also increases and the collector voltage becomes less positive. Again on the other hand we can see, in the negative half cycle of input potential, the base voltage with respect to the emitter becomes less positive potential due to which the emitter current decreases.

Note: We can say that, with the decrease in emitter current, the collector current also decreases. Due to which the voltage across the load resistance decreases. Then the collector voltage becomes more positive. In this way, we can say, the phase difference between the input and output potential is one eighty degree