CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2002

  • question_answer
     If \[{{l}_{1}},{{l}_{2}},{{l}_{3}},\]are the lengths of the emitter, base and collector of a transistor, then:

    A) \[{{l}_{3}}<{{l}_{2}}<{{l}_{1}}\]                  

    B) \[{{l}_{1}}={{l}_{2}}={{l}_{3}}\]

    C)  \[{{l}_{3}}<{{l}_{1}}<{{l}_{2}}\]                 

    D) (d \[{{l}_{3}}<{{l}_{1}}<{{l}_{2}}\]

    Correct Answer: C

    Solution :

    Ebers-Moll equation for transistor parameter. \[{{I}_{E}}={{I}_{pn}}(o)+{{I}_{np}}(o)\] \[{{a}_{11}}=Ae\left( \frac{{{D}_{p}}{{P}_{no}}}{W}+\frac{{{D}_{n}}n{{E}_{o}}}{{{L}_{E}}} \right)\] \[{{a}_{12}}=-\frac{Ae{{D}_{p}}{{P}_{no}}}{W}={{a}_{21}}\] \[{{a}_{22}}=Ae\left( \frac{{{D}_{p}}{{P}_{no}}}{W}+\frac{{{D}_{n}}{{n}_{Co}}}{{{L}_{C}}} \right)\] Here \[{{D}_{p}}({{D}_{n}})=\]diffusion constant for hole\[(\bar{e}){{m}^{2}}/\sec .\] \[W=\]base width \[{{L}_{E}},{{L}_{C}},{{L}_{B}}=\]Length of minority carries in E, C and B. Here \[{{L}_{B}}<{{L}_{E}}<{{L}_{C}}\] \[{{l}_{3}}>{{l}_{1}}>{{l}_{2}}\] Collector   ? is in 1-5 mm. Base       ? in \[\mu m.\] Emitter     ? 1 to 2 mm.


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