The input resistance of a common emitter transistor amplifier, if the output resistance is `500 kOmega`, the current gain `alpha=0.98` and the power gain is `6.0625 xx 10^(6)` is

Options

A. `198 Omega`
B. `300Omega`
C. `100Omega`
D. `400Omega`

Answer

A

Explanation

Voltage gain `=A_(V)=beta(R_(o))/(R_(i))`
Also, current gain `=beta=(alpha)/(1-alpha)=(0.98)/(1-0.98)=49`
`A_(V)=(49)((500xx10^(3))/(R_(i)))`
Power gain = current gain `xx` voltage gain
Power gain `=6.0625xx10(6)=49xx((500xx10^(3))/(R_(i)))xx49`
`rArr" "R_(i)=198Omega`