Physics - Semiconductors Question with Solution | TestHub

In a common emitter transistor amplifier, the input signal is applied between the base and the emitter, and the output is taken across the collector and the emitter.

When the input voltage increases during the positive half cycle, the forward bias across the base-emitter junction increases. This leads to an increase in the base current, which in turn causes a large increase in the collector current.

The output voltage is given by $V_{CE}=V_{CC}-I_C{R}_L$. As the collector current $I_C$ increases, the voltage drop across the load resistor $R_L$ increases, causing the output voltage $V_{CE}$ to decrease.

Thus, a positive change in the input voltage results in a negative change in the output voltage. This means that the output voltage is $180^{\circ }$ or ${\pi }^c$ out of phase with the input voltage.

Answer: ${\pi }^c$