NEET NEET SOLVED PAPER 2013

  • question_answer
    In a common emitter (CE) amplifier having a voltage gain G, the transistor used has trans conductance 0.03 mho and current gain 25. If the above transistor is replaced with another one with trans conductance 0.02 mho and current gain 20, the voltage gain will

    A) \[\frac{2}{3}G\]

    B) \[1.5G\]

    C) \[\frac{1}{3}G\]

    D) \[\frac{5}{4}G\]

    Correct Answer: A

    Solution :

    As\[{{A}_{v}}=\beta \frac{{{R}_{L}}}{{{R}_{i}}}\]         \[\left[ \because {{g}_{m}}=\frac{\Delta {{l}_{c}}}{\Delta {{V}_{B}}}=\frac{\Delta {{l}_{c}}}{\Delta {{l}_{B}}{{R}_{i}}} \right]\] or \[G=\left( \frac{\beta }{{{R}_{i}}} \right){{R}_{L}}\] \[\left[ \because {{g}_{m}}=\frac{\beta }{{{R}_{i}}} \right]\] \[\Rightarrow \] \[G={{g}_{m}}{{R}_{L}}\] \[\Rightarrow \] \[G\propto {{g}_{m}}\] \[\therefore \] \[\frac{{{G}_{2}}}{{{G}_{1}}}=\frac{{{g}_{{{m}_{1}}}}}{{{g}_{{{m}_{2}}}}}\] \[\Rightarrow \] \[{{G}_{2}}=\frac{0.02}{0.03}\times G\] \[\therefore \]Voltage gain \[{{G}_{2}}=\frac{2}{3}G\]


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