An amplifier is represented by the circuit shown in Fig. Here `r_(i)` is the input resistance of the amplifier and the voltage `V_(i)` is appearing across it. This voltage is amplified by a factor `A_(V)` and appears across the load as voltage `V_(0)`

An external voltage `V_(s)` is applied at the input terminals of the amplifier via series resistance `R_(S)`. What will be the apparent gain `A_(V)(=V_(0)//V_(s))` of the ampilifier in terms of `A_(V), R_(S)` and `r_(i).`

Explanation

Voltage gain, `A_(V)=V_(0)/V_(i)=400`
or `V_(0)=400V_(i)`
If `V_(s)` is the voltage of the source, then voltage across the input of the amplifier is
`V_(i)=(V_(s)xxr_(i))/(r_(i)R_(s))`
or `V_(s)=((r_(i)+R_(s))V_(i))/r_(i)`
Apparent voltage gain of amplifier,
`A_(V)^(')=V_(0)/V_(s)=(400V_(i)xxr_(i))/((r_(i)+R_(s))V_(i))=(400r_(i))/(r_(i)+R_(s))=(400xx100)/(100+300)=100`