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A transistor is used in common-emitter m...

A transistor is used in common-emitter mode in an amplifier circuit. When a signal 20mV is added to the base-emmiter voltage,the base current changes by `20(mu)A `and the collector current changes by 2mA.The load resistance is `5k(Omega)`.Calculate (a)the factor`(beta)`(b)the input resistance `R_(BE),`(c) the transconductance and (d) the voltage gain .

Text Solution

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(a)`beta`=(Delta)I_(C)/(Delta)I_(B)=2mA/20(mu)A=100.`
(b)The input resistance `R_(BE)=((Delta)V_(BE))/((Delta)I_(B)`
`20mV/20(mu)A=1k(Omega).`
(c )Transconductance`=(Delta)I_(C)/V_(BE)`
=2ma/20mV=0.1mho.`
(d)the change signal voltage is `R_L(Delta)I_c`
`=(5k Omega)(2mA)=10V.`
The applied signal vlotage =20mV.
Thus,the voltage gain is,
`10V/20mV=500.`
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