BHU PMT BHU PMT (Screening) Solved Paper-2008

  • question_answer
    The wavelength of the\[{{K}_{\alpha }}\]line for an element of atomic number 43 is\[\lambda .\]Then the wavelength of the\[{{K}_{\alpha }}\]line for an element of atomic number

    A)  \[\left( \frac{43}{29} \right)\lambda \]                 

    B)  \[\left( \frac{42}{28} \right)\lambda \]

    C)   \[\left( \frac{9}{4} \right)\lambda \]                     

    D)  \[\left( \frac{4}{9} \right)\lambda \]

    Correct Answer: C

    Solution :

                     Mosele/s law is given by \[\sqrt{v}=a(Z-b)\] For\[{{K}_{a}}\]line,\[b=1\]                 \[\sqrt{v}=a(Z-1)\] Squaring, we get                 \[v={{a}^{2}}{{(Z-1)}^{2}}\] or            \[\frac{c}{\lambda }={{a}^{2}}{{(Z-1)}^{2}}\] or            \[\lambda =\frac{c}{{{a}^{2}}{{(z-1)}^{2}}}\] For\[Z=43,\]wavelength\[=\lambda \] \[\therefore \]  \[\lambda =\frac{c}{{{a}^{2}}{{(43-1)}^{2}}}\] Or           \[\lambda =\frac{c}{{{a}^{2}}{{(42)}^{2}}}\] For\[Z=29,\]wavelength \[=\lambda '\] \[\lambda '=\frac{c}{{{a}^{2}}{{(29-1)}^{2}}}\]                   Or           \[\lambda '=\frac{c}{{{a}^{2}}{{(28)}^{2}}}\]                        ...(ii) Dividing Eq. (ii) by Eq. (i), we get \[\frac{\lambda '}{\lambda }={{\left( \frac{42}{28} \right)}^{2}}={{\left( \frac{3}{2} \right)}^{2}}\] \[\therefore \]  \[\lambda '=\left( \frac{9}{4} \right)\lambda \]                                 


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