Question

The output resistance of a common emitter transistor amplifier, if the input resistance is $ 200\,\Omega $ ( $ \alpha =0.98 $ and power gain is $ 5\times {{10}^{6}}, $ is)

• A. $ 516\,k\Omega $
• B. $ 216\,k\Omega $
• C. $ 300\,k\Omega $
• D. $ 416\,k\Omega $

Answer 1

Answer: (D)

We know that Voltage gain,
$ \Delta V=\beta \frac{{{R}_{o}}}{{{R}_{i}}} $
Also, $ \beta =\frac{\alpha }{1-\alpha }=\frac{0.98}{1-0.98}=49 $
$ \Delta V=(49)\left( \frac{{{R}_{0}}}{200} \right) $
Power gain AP
$ \Delta P $ = Current gain $ (\beta )\times $ voltage gain $ (\Delta V) $
$ \Rightarrow $ $ 5\times {{10}^{6}}=49\times 49\times \frac{{{R}_{o}}}{200} $
$ \Rightarrow $ $ {{R}_{e}}=\frac{5\times {{10}^{6}}\times 200}{49\times 49}=0.416\times {{10}^{6}}\simeq 416\,k\Omega $