Punjab Medical Punjab - MET Solved Paper-2004

  • question_answer
    Taking Rydbergs constant \[{{R}_{H}}=1.097\times {{10}^{7}}m\] first and second wavelength of Balmer series in hydrogen spectrum, is:

    A) \[2000\overset{\text{o}}{\mathop{\text{A}}}\,,\,\,3000\overset{\text{o}}{\mathop{\text{A}}}\,\]         

    B) \[1575\overset{\text{o}}{\mathop{\text{A}}}\,,\,\,2960\overset{\text{o}}{\mathop{\text{A}}}\,\]

    C) \[6529\overset{\text{o}}{\mathop{\text{A}}}\,,\,\,4280\overset{\text{o}}{\mathop{\text{A}}}\,\]         

    D) \[6552\overset{\text{o}}{\mathop{\text{A}}}\,,\,\,4863\overset{\text{o}}{\mathop{\text{A}}}\,\]

    Correct Answer: D

    Solution :

    The wavelength of the lines in Balmer series is represented by,                 \[\frac{1}{\lambda }={{R}_{H}}\left[ \frac{1}{{{2}^{2}}}-\frac{1}{{{n}_{2}}^{2}} \right]\] For first wavelength                 \[\frac{1}{{{\lambda }_{1}}}=1.097\times {{10}^{7}}\left[ \frac{1}{{{2}^{2}}}-\frac{1}{{{3}^{2}}} \right]\]                       \[=1.524\times {{10}^{6}}m\] or            \[{{\lambda }_{1}}=\frac{1}{1.524\times {{10}^{6}}}=6.562\times {{10}^{-7}}\] or            \[{{\lambda }_{1}}=6562\overset{\text{o}}{\mathop{\text{A}}}\,\] For second wavelength                 \[\frac{1}{{{\lambda }_{1}}}=1.097\times {{10}^{-7}}\left[ \frac{1}{{{2}^{2}}}-\frac{1}{{{4}^{2}}} \right]\]                      \[=2.056\times {{10}^{6}}\] or            \[{{\lambda }_{2}}=\frac{1}{2.056\times {{10}^{6}}}\] or            \[{{\lambda }_{2}}=4.863-7\times 10\times {{10}^{-10}}\] or            \[{{\lambda }_{2}}=4863\overset{\text{o}}{\mathop{\text{A}}}\,\]


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