JEE Main & Advanced Physics Nuclear Physics And Radioactivity Question Bank Critical Thinking

  • question_answer
    A double charged lithium atom is equivalent to hydrogen whose atomic number is 3. The wavelength of required radiation for emitting electron from first to third Bohr orbit in \[L{{i}^{++}}\] will be (Ionisation energy of hydrogen atom is 13.6eV)                                                                       [UPSEAT 1999]

    A)            182.51 Å                                 

    B)            177.17 Å

    C)            142.25 Å                                 

    D)            113.74 Å

    Correct Answer: D

    Solution :

               \[{{E}_{n}}=-13.6\frac{{{Z}^{2}}}{{{n}^{2}}}eV.\] Required energy for said transition                    \[\Delta E={{E}_{3}}-{{E}_{1}}=13.6\ {{Z}^{2}}\left[ \frac{1}{{{1}^{2}}}-\frac{1}{{{3}^{2}}} \right]\]                    \[\Rightarrow \Delta E=13.6\times {{3}^{2}}\left[ \frac{8}{9} \right]=108.8\ eV\]                    \[\Rightarrow \Delta E=108.8\times 1.6\times {{10}^{-19}}J\]                    Now \[\Delta E=\frac{hc}{\lambda }=108.8\times 1.6\times {{10}^{-19}}\]                    \[\Rightarrow \lambda =\frac{6.6\times {{10}^{-34}}\times 3\times {{10}^{8}}}{108.8\times 1.6\times {{10}^{-19}}}=0.11374\times {{10}^{-7}}m\]\[=113.74{\AA}\]


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