JEE Main & Advanced Physics Atomic Physics Question Bank Atomic Structure

  • question_answer
    Every series of hydrogen spectrum has an upper and  lower limit in wavelength. The spectral series which has an upper limit of wavelength equal to 18752 Å is            [MP PMT 1993]

    A)            Balmer series                       

    B)            Lyman series

    C)            Paschen series                    

    D)            Pfund series (Rydberg constant \[R=1.097\times {{10}^{7}}\]per metre)

    Correct Answer: C

    Solution :

                       \[\frac{1}{\lambda }=R\,\left[ \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right]\] \[\Rightarrow \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}}=\frac{1}{R\lambda }\]                    \[=\frac{1}{1.097\times {{10}^{7}}\times 18752\times {{10}^{-10}}}\]\[=0.0486=\frac{7}{144}.\] But            \[\frac{1}{{{3}^{2}}}-\frac{1}{{{4}^{2}}}=\frac{7}{144}\Rightarrow {{n}_{1}}=3\] and n2 = 4 (Paschen series)


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