KVPY Sample Paper KVPY Stream-SX Model Paper-27

  • question_answer
    Hydrogen (H), deuterium [D], singly ionized helium \[\left( H{{e}^{+}} \right)\]and doubly ionized lithium \[\left( L{{i}^{++}} \right)\]all have one electron around the nucleus. Consider \[n=\text{2}\] to \[n=1\] transition. The wavelengths of emitted radiations are \[{{\lambda }_{1}},{{\lambda }_{2}},{{\lambda }_{3}}\]and \[{{\lambda }_{4}}\] respectively. Then approximately:

    A) \[{{\lambda }_{1}}={{\lambda }_{2}}=4{{\lambda }_{3}}=9{{\lambda }_{4}}\]

    B) \[4{{\lambda }_{1}}=2{{\lambda }_{2}}=2{{\lambda }_{3}}={{\lambda }_{4}}\]

    C) \[{{\lambda }_{1}}=2{{\lambda }_{2}}=2\surd 2{{\lambda }_{3}}=3\surd 2{{\lambda }_{4}}\]

    D) \[{{\lambda }_{1}}={{\lambda }_{2}}=2{{\lambda }_{3}}=3\surd 2{{\lambda }_{4}}\]

    Correct Answer: A

    Solution :

    \[{{Z}_{1}}=1,{{Z}_{2}}=1,{{Z}_{3}}=2\operatorname{and}\,{{Z}_{4}}=3\]
                \[\frac{1}{\lambda }=R{{Z}^{2}}\left( \frac{1}{{{1}^{2}}}-\frac{1}{{{2}^{2}}} \right)\]
    Or         \[\lambda =\frac{4}{3R{{Z}^{2}}}\]
    Or         \[\lambda {{Z}^{2}}=\operatorname{constant}\]
    So \[{{\lambda }_{1}}{{\left( 1 \right)}^{2}}={{\lambda }_{2}}{{\left( 1 \right)}^{2}}={{\lambda }_{3}}{{\left( 2 \right)}^{2}}=\lambda a\left( {{3}^{2}} \right)\]
    Or \[{{\lambda }_{1}}={{\lambda }_{2}}=4{{\lambda }_{3}}=9{{\lambda }_{4}}\]


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