BCECE Engineering BCECE Engineering Solved Paper-2013

  • question_answer
    Wave number of spectral line for a given transition is \[x\,c{{m}^{-1}}\]for \[\text{H}{{\text{e}}^{\text{+}}}\text{,}\]then its value for \[B{{e}^{3+}}\](isoelectronic of\[H{{e}^{+}},\]) for same transition is

    A) \[\frac{x}{4}c{{m}^{-1}}\]            

    B)        \[x\,c{{m}^{-1}}\]

    C) \[4x\,c{{m}^{-1}}\]         

    D)        \[16x\,c{{m}^{-1}}\]

    Correct Answer: C

    Solution :

    \[\bar{v}\](wave number) \[={{\bar{R}}_{H}}{{Z}^{2}}\left[ \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right]\] \[{{\bar{v}}_{1}}(H{{e}^{+}},Z=2)={{\bar{R}}_{H}}{{(2)}^{2}}\left[ \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right]\] \[{{\bar{v}}_{2}}(B{{e}^{3+}},Z=4)={{\bar{R}}_{H}}={{(4)}^{2}}\left[ \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right]\] \[\therefore \]  \[\frac{{{v}_{2}}}{{{v}_{1}}}=\frac{{{(4)}^{2}}}{{{(2)}^{2}}}\] \[=\frac{16}{4}=4\]                 \[\therefore \]  \[{{\bar{v}}_{2}}=4{{\bar{v}}_{1}}\]                                 \[{{\bar{v}}_{2}}=4\times c{{m}^{-1}}\]


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