CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2011

  • question_answer
    Which transition in the hydrogen atomic spectrum will have the same wavelength as the transition,\[n=4\]to\[n=2\]of\[H{{e}^{+}}\]spectrum?

    A)  \[n=4\]to\[n=3\]     

    B)         \[n=3\]to\[n=2\]

    C)  \[n=4\] to\[n=2\]   

    D)        \[n=3\]to \[n=1\]

    E) \[~n=2\] to\[n=1\]

    Correct Answer: E

    Solution :

    According to Rydbergs formula \[\frac{1}{\lambda }=R\left( \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right){{Z}^{2}}\] For\[H{{e}^{+}}\]ion;\[Z=2,{{n}_{1}}=2\]and \[{{n}_{2}}=4\] \[\therefore \]  \[\frac{1}{\lambda }=R\left( \frac{1}{{{2}^{2}}}-\frac{1}{{{4}^{2}}} \right)\times {{2}^{2}}\]                 \[=R\times \frac{3}{16}\times 4\]                 \[\frac{1}{\lambda }=\frac{3R}{4}\] Or           \[\lambda =\frac{4}{3R}\] For getting the same value of wavelength in hydrogen atomic spectrum, the values of\[{{n}_{1}}\]and\[{{n}_{2}}\]must be 1 and 2 respectively. \[\therefore \]  \[\frac{1}{\lambda }=R\left( \frac{1}{{{1}^{2}}}-\frac{1}{{{2}^{2}}} \right)\times {{1}^{2}}\]                 \[\frac{1}{\lambda }=\frac{3R}{4}\] Or           \[\lambda =\frac{4}{3R}\]


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