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

  • question_answer
    A hydrogen like atom of atomic number Z is in an excited state of quantum number 2n. It can emit a maximum energy photon of 204 eV. If it makes a transition to quantum state n, a photon of energy 40.8 eV is emitted. The value of  n will be                   [Based onIIT-JEE (Mains) 2000]

    A)            1    

    B)            2

    C)            3    

    D)            4

    Correct Answer: B

    Solution :

               Let ground state energy (in eV) be \[{{E}_{1}}\]                    Then from the given condition                    \[{{E}_{2n}}-{{E}_{1}}=204\,eV\] or \[\frac{{{E}_{1}}}{4{{n}^{2}}}-{{E}_{1}}=204\,eV\]                    Þ \[{{E}_{1}}\left( \frac{1}{4{{n}^{2}}}-1 \right)=204\,eV\]                       ?..(i)                    and \[{{E}_{2n}}-{{E}_{n}}=40.8\,eV\]                    Þ \[\frac{{{E}_{1}}}{4{{n}^{2}}}-\frac{{{E}_{1}}}{{{n}^{2}}}={{E}_{1}}\left( -\frac{3}{4{{n}^{2}}} \right)=40.8\,eV\]            ?..(ii)                    From equation (i) and (ii),  \[\frac{1-\frac{1}{4{{n}^{2}}}}{\frac{3}{4{{n}^{2}}}}=5\] Þ \[n=2\]


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