Given:
Voltage gain (Av) = 50
Input impedance (Zi) = 100 ohms
Power gain (Ap) = 1250

To find:
Output impedance (Zo)

Solution:

Formula:
Power gain (Ap) = Voltage gain (Av)^2 / Input impedance (Zi)

Substituting the given values in the formula, we get:
1250 = 50^2 / 100
1250 = 2500 / Zi
Zi = 2 ohms

Formula:
Output impedance (Zo) = Input impedance (Zi) / Voltage gain (Av)

Substituting the given values in the formula, we get:
Zo = 2 / 50
Zo = 0.04 ohms

Therefore, the output impedance of the common emitter amplifier is 0.04 ohms.

Explanation:

- Common emitter amplifier: It is a type of transistor amplifier in which the emitter terminal is common to both the input and output circuits.
- Voltage gain (Av): It is the ratio of output voltage to input voltage of the amplifier. In this case, the voltage gain is given as 50.
- Input impedance (Zi): It is the impedance offered by the input circuit of the amplifier to the signal source. In this case, the input impedance is given as 100 ohms.
- Power gain (Ap): It is the ratio of output power to input power of the amplifier. In this case, the power gain is given as 1250.
- Output impedance (Zo): It is the impedance offered by the output circuit of the amplifier to the load. We need to find this value.

Using the formula for power gain, we can calculate the input impedance of the amplifier as 2 ohms.
Using the formula for output impedance, we can calculate the output impedance of the amplifier as 0.04 ohms.

Hence, we have found the output impedance of the common emitter amplifier.