BHU PMT BHU PMT (Screening) Solved Paper-2011

  • question_answer
    An electron in hydrogen atom first jumps from second excited state to first excited state and then from first excited state to ground state. Let the ratio of wavelength, momentum and energy of photons emitted in these two cases be a, b and c respectively. Then

    A)  \[a=\frac{9}{4}\]                             

    B)  \[b=\frac{27}{5}\]

    C)  \[c=\frac{5}{27}\]                           

    D)  \[c=\frac{1}{a}=\frac{5}{27}\]

    Correct Answer: C

    Solution :

                     First transition is from\[n=3\]to\[n=2,\]second transition is from\[n=2\]to\[n=1\] \[\therefore \]  \[\frac{{{E}_{1}}}{{{E}_{2}}}=c=\frac{\frac{1}{{{2}^{2}}}-\frac{1}{{{3}^{2}}}}{\frac{1}{{{1}^{2}}}-\frac{1}{{{2}^{2}}}}\] or            \[c=\frac{5/36}{3/4}=\frac{5}{36}\times \frac{4}{3}=\frac{5}{27}\] As, \[p=\frac{E}{c'}\], therefore                 \[\frac{{{p}_{1}}}{{{p}_{2}}}=b=\frac{{{E}_{1}}}{{{E}_{2}}}=c,\]i.e., \[b=c=\frac{5}{27}\] As,          \[E=\frac{hc}{\lambda }\] \[\therefore \]  \[\lambda \propto \frac{1}{E}\]


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