BCECE Medical BCECE Medical Solved Papers-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 \[\overset{o}{\mathop{A}}\,\]      

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

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

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

    Correct Answer: D

    Solution :

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


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