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NEET Physics Semiconducting Devices NEET PYQ-Semiconducting Devices

  • question_answer
    A transistor is operated in common emitter configuration at constant collector voltage \[{{V}_{c}}=1.5\text{ }V\] such that a change in the base current from \[100\,\,\mu A\]  to \[150\,\,\mu A\] produces a change in the collector current from 5 mA to 10 mA. The current gain \[(\beta )\] is:                                                                                     [AIPMT (S) 2006]

    A)  67     

    B)                   75       

    C)  100  

    D)  50

    Correct Answer: C

    Solution :

    AC current gain \[\beta \] is defined as the ratio of the collector to the base current at constant collector voltage,
                            \[\beta =\left( \frac{\Delta {{i}_{C}}}{\Delta {{i}_{B}}} \right){{v}_{c}}\]
    Given,   \[\Delta {{i}_{C}}=10\,mA-5\,mA=5\,mA\]
                            \[\Delta {{i}_{B}}=150\,\mu A-100\,\mu A=50\,\mu A\]
    \[\therefore \]      \[\beta =\frac{5\,mA}{50\times {{10}^{-3}}\,mA}=100\]
    Note:    In common emitter amplifier, the output voltage signal is \[{{180}^{o}}\] out of phase with the input voltage signal.


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