Haryana PMT Haryana PMT Solved Paper-2003

  • question_answer
    Given the wavelength of first member of Lyman series is \[1215\overset{\text{o}}{\mathop{\text{A}}}\,\]. The wavelength of Ha line is :

    A) \[6561\overset{\text{o}}{\mathop{\text{A}}}\,\]

    B) \[5464\overset{\text{o}}{\mathop{\text{A}}}\,\]

    C) \[800\overset{\text{o}}{\mathop{\text{A}}}\,\]

    D) \[4840\overset{\text{o}}{\mathop{\text{A}}}\,\]

    Correct Answer: A

    Solution :

                    Using relation \[\frac{1}{\lambda }=R\left( \frac{1}{{{n}_{1}}^{2}{{n}_{2}}^{2}} \right)\] For Lyman series \[{{n}_{1}}=1,\,{{n}_{2}}=2\] So,          \[\frac{1}{{{\lambda }_{L}}}=R\left( \frac{1}{{{1}^{2}}}-\frac{1}{{{2}^{2}}} \right)=\frac{3R}{4}\]       ??(1) For \[{{H}_{\alpha }}\] line \[{{n}_{1}}=2,{{n}_{2}}=3\]                 \[\frac{1}{{{\lambda }_{H\alpha }}}=R\left( \frac{1}{{{2}^{2}}}-\frac{1}{{{3}^{2}}} \right)=\frac{5R}{36}\]        ?..(2) From Eqs. (1) and (2),  \[\frac{{{\lambda }_{H\alpha }}}{{{\lambda }_{L}}}=\frac{3}{4}\times \frac{36}{5}\]                 \[=\frac{27}{5}\]                 \[{{\lambda }_{H\alpha }}=\frac{27}{5}\times 1215\]                 \[=6561\overset{\text{o}}{\mathop{\text{A}}}\,\]


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