BCECE Engineering BCECE Engineering Solved Paper-2001

  • question_answer
    The energy gap of silicon is 1.14 eV. The maximum wavelength at which silicon will begin absorbing energy is:

    A)  \[18.855\,\overset{\text{o}}{\mathop{\text{A}}}\,\]    

    B)  \[108.55\,\overset{\text{o}}{\mathop{\text{A}}}\,\]    

    C)         \[1085.5\,\overset{\text{o}}{\mathop{\text{A}}}\,\]    

    D)         \[10855\,\overset{\text{o}}{\mathop{\text{A}}}\,\]

    Correct Answer: D

    Solution :

    Energy absorbed by silicon is given by \[\Delta \Epsilon =\frac{hc}{\lambda }\]or \[\lambda =\frac{hc}{\Delta \Epsilon }\] Here,     \[h=6.6\times {{10}^{-34}}\,J-s,\]\[c=3\times {{10}^{8}}\,m/s,\] \[\Delta \Epsilon =1.14\,eV=1.14\times 1.6\times {{10}^{-19}}J\] \[\therefore \]  \[\lambda =\frac{6.6\times {{10}^{-34}}\times 3\times {{10}^{8}}}{1.14\times 1.6\times {{10}^{-19}}}\]                                 \[=10.855\times {{10}^{-7}}\]                                 \[=10855\,\overset{\text{o}}{\mathop{\text{A}}}\,\] Note: After putting the values of and c in the expression for energy, we get \[\Delta E=\frac{12375}{\lambda (\overset{\text{o}}{\mathop{\text{A}}}\,)}eV\]                 or            \[\lambda =\frac{12375}{\Delta E(eV)}\overset{\text{o}}{\mathop{\text{A}}}\,\]


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