VIT Engineering VIT Engineering Solved Paper-2010

  • question_answer
    According to the Bohrs theory of hydrogen atom, the speed of the electron, energy and the radius of its orbit vary with the principal quantum number n, respectively, as

    A)  \[\frac{1}{n},\frac{1}{{{n}^{2}}},{{n}^{2}}\]

    B)  \[\frac{1}{n},{{n}^{2}}\frac{1}{{{n}^{2}}}\]

    C)  \[{{n}^{2}},\frac{1}{{{n}^{2}}},{{n}^{2}}\]      

    D)  \[n,\frac{1}{{{n}^{2}}},\frac{1}{{{n}^{2}}}\]  

    Correct Answer: A

    Solution :

    According to Bohrs theory of hydrogen atom, (i) The speed of the electron in the nth orbit is  \[{{v}_{n}}=\frac{1}{n}\,\frac{{{e}^{2}}}{4\pi {{\varepsilon }_{0}}(h/2\pi )}\] or \[{{v}_{n}}\alpha \frac{1}{n}\]        (ii) The energy of the electron in the nth orbit is          \[{{E}_{n}}=-\frac{m{{e}^{4}}}{8{{n}^{2}}\varepsilon _{0}^{2}{{h}^{2}}}=\frac{-13.6}{{{n}^{2}}}eV\] or \[{{E}_{n}}\,\,\alpha \,\,\frac{1}{{{n}^{2}}}\] (iii) The radius of the electron in the nth orbit is \[{{r}_{n}}=\frac{{{n}^{2}}{{h}^{2}}{{\varepsilon }_{0}}}{\pi m{{e}^{2}}}={{n}^{2}}{{a}_{0}}\] where \[{{a}_{0}}=\frac{{{h}^{2}}{{\varepsilon }_{0}}}{\pi me}=5.29\times {{10}^{-11}}m,\], is called Bohrs radius,                                           or                     \[{{r}_{n}}\,\,\alpha \,\,\,{{n}^{2}}\]


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