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Question:

Draw a circuit diagram of a C.E. transistor amplifier. Briefly explain its working and write the expression for (i) current gain, (ii) voltage gain of the amplifier.

Solution:

Voltage gain = it is equal the ratio of small change in output voltage at collector to that of change in input voltage
AV=OutputvoltageInputvoltage=ΔVCEΔVEB=(ΔIC)RoutΔIBRin
AV=βAC×RoutRin
Where βACis AC current gain
Relation between input and output signals of n-p-n transistor amplifier, when positive half cycle is fed into input circuit, forward bias of emitter base circuit decrease, i.e collector current decrease , output voltage. Vo=VCE−ICRLDecrease in collector current cause increase of output voltage.