J & K CET Engineering J and K - CET Engineering Solved Paper-2006

  • question_answer
    The shortest wavelength in Lyman series is\[91.2\text{ }nm\]. The longest wavelength of the series   is                                  

    A)  \[121.6\text{ }nm\]    

    B)  \[182.4\text{ }nm\]

    C)  \[243.4\text{ }nm\]    

    D)  \[364.8\text{ }nm\]

    Correct Answer: A

    Solution :

    The wavelength (X) of lines is given by \[\frac{1}{\lambda }=R\left( \frac{1}{{{1}^{2}}}-\frac{1}{{{n}^{2}}} \right)\] For Lyman series, the shortest wavelength is for \[n=\infty \] and longest is for \[n=2\]. \[\therefore \] \[\frac{1}{{{\lambda }_{S}}}=R\left( \frac{1}{{{1}^{2}}} \right)\] ?..(i) \[\frac{1}{{{\lambda }_{L}}}=R\left( \frac{1}{1}-\frac{1}{{{2}^{2}}} \right)=\frac{3}{4}R\] ??(ii) Dividing Eq. (ii) by Eq. (i) we; get \[\frac{{{\lambda }_{L}}}{{{\lambda }_{S}}}=\frac{4}{3}\] Given, \[{{\lambda }_{S}}=91.2nm\] \[\Rightarrow \] \[{{\lambda }_{L}}=91.2\times \frac{4}{3}=121.6nm\]


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