CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2010

  • question_answer
    The wave number of the spectral line in the emission spectrum of hydrogen will be equal to \[\frac{8}{9}\] times the Rydberg's constant if the electron jumps from

    A) \[n=3\] to \[n=1\]           

    B) \[n=10\] to \[n=1\]

    C) \[n=9\] to \[n=1\]           

    D) \[n=2\] to \[n=1\]

    Correct Answer: A

    Solution :

    Wave number of spectral line in emission spectrum of hydrogen,                 \[\overline{v}={{R}_{H}}\left( \frac{1}{{{n}^{2}}}-\frac{1}{n_{2}^{2}} \right)\]                      …. (i) Given,   \[\overline{v}=\frac{8}{9}{{R}_{H}}\] On putting the value of v in Eq. (i), we get                                 \[\frac{8}{9}{{R}_{H}}={{R}_{H}}\left( \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right)\]                                 \[\frac{8}{9}=\frac{1}{{{(1)}^{2}}}-\frac{1}{n_{2}^{2}}\]                                 \[\frac{8}{9}-1=-\frac{1}{n_{2}^{2}}\]                                 \[\frac{1}{3}-\frac{1}{{{n}_{2}}}\]                 \[\therefore \]  \[{{n}_{2}}=3\] Hence, electron jumps from \[{{n}_{2}}=3\] to \[{{n}_{1}}=1\]


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