RAJASTHAN PMT Rajasthan - PMT Solved Paper-2009

  • question_answer
    If the frequency of\[{{K}_{\alpha ,}}\] X-ray of the element of atomic number 31 is\[f,\] then the frequency of\[{{K}_{\alpha ,}}\] X-ray for atomic number 51 is

    A)  25/9 \[f\]                           

    B)  16/25\[f\]

    C)  9/25 \[f\]           

    D)         zero

    Correct Answer: A

    Solution :

    Wavelength of\[{{K}_{\alpha }},\]\[X-\]ray \[\propto \frac{1}{{{(Z-1)}^{2}}}\] \[\therefore \]  \[\frac{{{\lambda }_{2}}}{{{\lambda }_{1}}}=\frac{{{(Z-1)}^{2}}}{{{({{Z}_{2}}-1)}^{2}}}\] But,        \[\lambda \propto \frac{1}{frequency(f)}\] \[\therefore \]  \[\frac{{{f}_{1}}}{{{f}_{2}}}=\frac{{{({{Z}_{1}}-1)}^{2}}}{{{({{Z}_{2}}-1)}^{2}}}\] or            \[\frac{f}{{{f}_{2}}}=\frac{{{(31-1)}^{2}}}{{{(51-1)}^{2}}}=\frac{900}{2500}\] \[\therefore \]  \[{{f}_{2}}=\frac{25}{9}f\]


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