J & K CET Medical J & K - CET Medical Solved Paper-2007

  • question_answer
    If a is radius of first Bohr orbit in hydrogen atom, the radius of the third orbit is

    A)  3a                                         

    B)  9a         

    C)  27a                                       

    D)  81a

    Correct Answer: B

    Solution :

                     Radius of Bohr orbit is given by \[{{r}_{n}}=\left( \frac{{{\varepsilon }_{0}}{{h}^{2}}}{\pi m{{e}^{2}}} \right){{n}^{2}}\] The quantities in the bracket are constant. \[\therefore \]                  \[{{r}_{n}}\propto {{n}^{2}}\]     The expression gives the radius of nth Bohr orbit \[\therefore \]  \[\frac{{{r}_{1}}}{{{r}_{2}}}=\frac{n_{1}^{2}}{n_{2}^{2}}\] \[\Rightarrow \]               \[\frac{a}{{{r}_{2}}}=\frac{1}{{{3}^{2}}}\] \[{{r}^{2}}=9a\]


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