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CMC Medical CMC-Medical VELLORE Solved Paper-2014

  • question_answer
    Pure silicon at 300K has equal electron\[({{n}_{e}})\]and hole \[({{n}_{h}})\]concentration of \[1.5\times {{10}^{16}}{{m}^{-3}}.\] Doping by indium increase \[({{n}_{h}})\] to \[4.5\times {{10}^{22}}{{m}^{-3}}.\] The\[({{n}_{e}})\]in the doped silicon is

    A)  \[9\times {{10}^{5}}\]                  

    B)  \[5\times {{10}^{9}}\]

    C)  \[2.25\times {{10}^{11}}\]                          

    D)  \[3\times {{10}^{19}}\]

    Correct Answer: B

    Solution :

                    \[{{n}_{e}}{{n}_{h}}={{({{n}_{i}})}^{2}}\] \[{{n}_{e}}\times 4.5\times {{10}^{22}}={{(1.5\times {{10}^{16}})}^{2}}\]      \[{{n}_{e}}=\frac{2.25\times {{10}^{32}}}{4.5\times {{10}^{22}}}\]      \[{{n}_{e}}=5\times {{10}^{9}}\]


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