CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2003

  • question_answer
    In a n-p-n transistor amplifier, the collector current is 9 mA. If 90% of the electrons from the emitter reach the collector, then:

    A)  \[\alpha =0.9,\beta =9.0\]

    B)  the base current is 10 mA

    C)  the emitter current is 1 mA

    D)  \[\alpha =9.0,\text{ }\beta =0.9\]

    E)  \[\alpha =0.99,\text{ }\beta =99.0\]

    Correct Answer: A

    Solution :

    Let\[{{I}_{e}}\]be the emitter current. \[\therefore \]  \[\frac{90}{100}\times {{I}_{e}}={{I}_{c}}\] \[\Rightarrow \]               \[{{I}_{e}}=\frac{100{{I}_{c}}}{90}=\frac{10}{9}{{I}_{c}}\] \[\therefore \]  \[\alpha =\frac{{{I}_{c}}}{{{I}_{e}}}=\frac{9}{10}=0.9\] And        \[\beta =\frac{{{I}_{c}}}{{{I}_{b}}}=\frac{{{I}_{c}}}{{{I}_{e}}-{{I}_{c}}}\]                 \[=\frac{1}{\frac{{{I}_{e}}}{{{I}_{c}}}-1}\]                 \[=\frac{1}{10/9-1}\]                 \[=\frac{9}{1}=9\]


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