A`p-n-p` transistor is used in common-emitter mode in an amplifier circuuit. A change of `40muA` in the base current brings a change of `2mA` in collector current and `0.04V` in base-emitter volatage. Find the
(a) input resistance `r_(i)` and
(b) the base current amplification factor `(beta)`.
(c ) if a load of `6kOmega` is used, then also find the voltage gain of the amplifier.

Explanation

Given `DeltaI_(B)=40muA=40xx10^(-6)A`
`DeltaI_(C)=2mA=2xx10^(-3)A`
`DeltaV_(BE)=0.04"volt",R_(L)=6kOmega=6xx10^(3)Omega`
(1) input resistance `R_("input")=(DeltaV_(BE))/(DeltaI_(B))=(0.04)/(40xx10^(-6))=10^(3)Omega=1kOmega`
(2) Current amplification factor, `beta=(DeltaI_(C))/(DeltaI_(B))=(2xx10^(-3))/(40xx10^(-6))=50`
(3). Voltage gain in common-emitter configuration,
`A_(upsilon)=beta(R_(L))/(R_("inp."))=50xx(6xx10^(3))/(1xx10^(3))=300`