JEE Main & Advanced JEE Main Paper (Held On 25 April 2013)

  • question_answer
                    A 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature. It will emit:     JEE Main Online Paper ( Held On 25  April 2013 )

    A)                 2 lines in the Lyman series and I line in the Balmar series

    B)                                        3 lines in the Lyman series

    C)                                        1 line in the Lyman series and 2 lines in the balmar series

    D)                                        3 lines in the balmer series

    Correct Answer: A

    Solution :

                    \[E=\frac{hc}{\lambda }\Rightarrow \lambda =\frac{hc}{E}=\frac{6.62\times {{10}^{-34}}\times 3\times {{10}^{8}}}{12.5\times 1.6\times {{10}^{-19}}}\] \[=993{\AA}\] \[\frac{1}{\lambda }=R\left( \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right)\] (where Rydberg constant, \[R=1.097\times {{10}^{7}}\]) or\[\frac{1}{993\times {{10}^{-10}}}=1.097\times {{10}^{7}}\left( \frac{1}{{{1}^{2}}}-\frac{1}{n_{2}^{2}} \right)\] Solving we get \[{{n}_{2}}=3\]Spectral lines Total number of spectral lines =3 Two lines in Lyman series for \[{{n}_{1}}=1,{{n}_{2}}=2\]and \[{{n}_{1}}=1,{{n}_{2}}=3\] and one in Balmer series for \[{{n}_{1}}=2,{{n}_{2}}=3\]


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