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 .

Answer

A, B, C, D

Explanation

(a) Factor ` beta `
` beta = (Delta i_c) / (Delta i_b) `
Substituiting the given values, we have
` beta = (2 xx 10^(-3)) / (20 xx 10^(-6)) = 100`
(b) Input Resistance `R_"in"
`R_"in" = (Delta V_(BE) )/( Delta i_b) =( 20 xx 10^(-3)) / (20 xx 10^(-6)) `
` 10^(3) Omega `
` 1 k Omega`
( c) Transconductance `g_m `
` g_m = (Delta i_c )/( Delta V_(BE)) = (2 xx 10^(-3)) / (20 xx 10^(-3))
` = 0.1 mho `
(d ) Voltage Gain ` A_V `
` A_V = beta (R_"out" / R_"in" ) `
Substituting the values we have ,
` A_V = (100) ((5 xx 10^(3) )/( 1 xx 10^(3) )) `
` = 500 `