JEE Main & Advanced Physics Atomic Physics Question Bank Atomic Structure

  • question_answer
    If the wavelength of the first line of the Balmer series of hydrogen is\[6561\ {AA}\], the wavelength of the second line of the series should be                                [CPMT 1984; DPMT 2004]

    A) \[13122\ {AA}\]                 

    B) \[3280\ {AA}\]

    C) \[4860\ {AA}\]                   

    D) \[2187\ {AA}\]

    Correct Answer: C

    Solution :

    The wavelength of spectral line in Balmer series is given by \[\frac{1}{\lambda }=R\,\left[ \frac{1}{{{2}^{2}}}-\frac{1}{{{n}^{2}}} \right]\] For first line of Balmer series, n = 3 Þ \[\frac{1}{{{\lambda }_{1}}}=R\,\left[ \frac{1}{{{2}^{2}}}-\frac{1}{{{3}^{2}}} \right]=\frac{5R}{36}\];     For second line n = 4. Þ \[\frac{1}{{{\lambda }_{2}}}=R\,\left[ \frac{1}{{{2}^{2}}}-\frac{1}{{{4}^{2}}} \right]=\frac{3R}{16}\]      \ \[\frac{{{\lambda }_{2}}}{{{\lambda }_{1}}}=\frac{20}{27}\Rightarrow {{\lambda }_{1}}=\frac{20}{27}\times 6561=4860\,{\AA}\]


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