Question

The output voltage of a voltage amplifier has been found to decrease by 20% when a load resistance of 1 k is connected. What is the value of the amplifier output resistance?

Answer 1

We use the voltage division problem  between the load resistance, amplifier output resistance as

$V_{out} = V_{amlifire} \times \frac{R_{load} }{R_{load} + R_{out} }$.

Here, $V_{out}$ is the output voltage, $V_{amlifire}$ is the amplifier voltage, $R_{load}$ is the load resistance and $R_{out}$ is the amplifier output resistance.

Therefore,

$1-\frac{20}{100} = \frac{1 \ k\Omega }{1 \ k\Omega +R_{out} } \\\\ R_{out} = \frac{1 \ k\Omega }{0.8} -1 \ k\Omega =1250 \Omega -1000 \Omega =250 \Omega$.

Thus, the amplifier output resistance is $250 \ \Omega$.