CMC Medical CMC-Medical Ludhiana Solved Paper-2008

  • question_answer
    If the wavelength of the first line of the Balmer series of hydrogen is 6561\[\overset{\text{o}}{\mathop{\text{A}}}\,\], the wavelength of the second line of the series should be

    A)  13122 \[\overset{\text{o}}{\mathop{\text{A}}}\,\]                        

    B)  3280 \[\overset{\text{o}}{\mathop{\text{A}}}\,\]

    C)  4860 \[\overset{\text{o}}{\mathop{\text{A}}}\,\]                          

    D)  2187 \[\overset{\text{o}}{\mathop{\text{A}}}\,\]

    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 \[\Rightarrow \]                               \[\frac{1}{{{\lambda }_{1}}}=R\left[ \frac{1}{{{2}^{2}}}-\frac{1}{{{3}^{2}}} \right]\]                                 \[=\frac{5R}{36}\] For second line, n = 4 \[\frac{1}{{{\lambda }_{2}}}=R\left[ \frac{1}{{{2}^{2}}}-\frac{1}{{{4}^{2}}} \right]=\frac{3R}{16}\] \[\therefore \]  \[\frac{{{\lambda }_{2}}}{{{\lambda }_{1}}}=\frac{20}{27}\] \[\Rightarrow \]               \[{{\lambda }_{2}}=\frac{20}{27}\times 6561=4860\overset{\text{o}}{\mathop{\text{A}}}\,\]


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