JEE Main & Advanced Physics Ray Optics JEE PYQ-Ray Optics

  • question_answer
    If the ratio of the concentration of electrons to that of holes in a semiconductor is\[\frac{7}{5}\]and the ratio of currents is \[\frac{7}{4}\], then what is the ratio of their drift velocities?        [AIEEE 2006]

    A) \[\frac{5}{8}\]

    B) \[\frac{4}{5}\]

    C) \[\frac{5}{4}\]

    D) \[\frac{4}{7}\]

    Correct Answer: C

    Solution :

    [c] \[l={{n}_{e}}A{{v}_{d}}\]
    \[\therefore \] \[\frac{{{l}_{e}}}{{{l}_{n}}}=\frac{{{n}_{e}}\times {{({{v}_{d}})}_{e}}}{{{n}_{h}}\times {{({{v}_{d}})}_{h}}}\]                       \[(\because {{A}_{1}}={{A}_{2}})\]
    Here    \[\frac{{{n}_{e}}}{{{n}_{h}}}=\frac{7}{5},\frac{{{l}_{e}}}{{{l}_{h}}}=\frac{7}{4}\]
    \[\therefore \]    \[\frac{7}{4}=\frac{7}{5}\times \frac{{{({{v}_{d}})}_{e}}}{{{({{v}_{d}})}_{h}}}\]
    \[\Rightarrow \] \[\frac{{{({{v}_{d}})}_{e}}}{{{({{v}_{d}})}_{h}}}=\frac{5}{7}\times \frac{7}{4}=\frac{5}{4}\]


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