Q198 / 200 · MHT CET - Medical 2026 (23 April Shift 2) · Physics
In a common emitter amplifier circuit using n-p-n transistor, the phase difference between the input and output voltages will be
- Correct answerA$180^\circ$
- B$135^\circ$
- C$90^\circ$
- D$45^\circ$
Solution
In a common emitter amplifier, the input signal is applied between the base and emitter, and the output is taken across the collector and emitter.
The output voltage is given by $V_{CE} = V_{CC} - I_C R_C$.
During the positive half cycle of the input signal, the forward bias across the base-emitter junction increases. This causes the base current $I_B$ to increase, which in turn increases the collector current $I_C$.
As $I_C$ increases, the voltage drop across the collector resistor $R_C$ increases. Consequently, the output voltage $V_{CE}$ decreases.
Thus, a positive input voltage results in a negative output voltage, indicating a phase reversal.
Therefore, the phase difference between the input and output voltages in a common emitter amplifier is $180^\circ$.
Answer: $180^\circ$
The output voltage is given by $V_{CE} = V_{CC} - I_C R_C$.
During the positive half cycle of the input signal, the forward bias across the base-emitter junction increases. This causes the base current $I_B$ to increase, which in turn increases the collector current $I_C$.
As $I_C$ increases, the voltage drop across the collector resistor $R_C$ increases. Consequently, the output voltage $V_{CE}$ decreases.
Thus, a positive input voltage results in a negative output voltage, indicating a phase reversal.
Therefore, the phase difference between the input and output voltages in a common emitter amplifier is $180^\circ$.
Answer: $180^\circ$
Hence, the correct answer is option: 'A'.