Question

The current gain in the common emitter amplifier mode of a transistor is $10$. The input impedance is $20k\Omega$ and load of resistance is $100k\Omega$. The power gain is :

• A. $300$
• B. $500$
• C. $200$
• D. $100$

Answer 1

Answer: (B)

$500$

The power gain is defined as the ratio of change in output to the change in input power.
Since, $P=VI$
Therefore,
Power gain $=$ Current gain $\times$ Voltage gain
$=\beta \times \beta \left(\frac{R_{out}}{R_{in}}\right)={\beta }^2\left(\frac{R_{out}}{R_{in}}\right)$
Given, $\beta =10$, $R_{in}=20k\Omega$ and $R_{out}=100k\Omega$
$\therefore$ Power gain $={\left(10\right)}^2\left(\frac{100}{20}\right)=100\times 5=500$