JEE Main & Advanced JEE Main Online Paper (Held On 23 April 2013)

  • question_answer
                    In the Bohr?s model of hydrogen- like atom the force between the nucleus and the electron is modified as                 \[\operatorname{F}=\frac{{{e}^{2}}}{4\pi {{\in }_{0}}}\left( \frac{1}{{{\operatorname{r}}^{2}}}+\frac{\beta }{{{\operatorname{r}}^{3}}} \right),\] Where \[\beta \]is a constant. For this atom, the radius of the \[{{\operatorname{n}}^{\operatorname{th}}}\] orbit in terms of the Bohr radius \[\left( {{a}_{0}}\frac{{{\in }_{0}}{{\operatorname{h}}^{2}}}{\operatorname{m}\pi {{e}^{2}}} \right)\] is     [JEE Main Online Paper ( Held On 23  April 2013 )

    A)                  \[{{\operatorname{r}}_{\operatorname{n}}}={{\operatorname{a}}_{0}}\operatorname{n}-\beta \]                     

    B)                                         \[{{\operatorname{r}}_{\operatorname{n}}}={{\operatorname{a}}_{0}}{{\operatorname{n}}^{2}}+\beta \]

    C)                                         \[{{\operatorname{r}}_{\operatorname{n}}}={{\operatorname{a}}_{0}}{{\operatorname{n}}^{2}}-\beta \]               

    D)                                         \[{{\operatorname{r}}_{\operatorname{n}}}={{\operatorname{a}}_{0}}\operatorname{n}+\beta \]

    Correct Answer: C

    Solution :

                      As\[F=\frac{m{{v}^{2}}}{r}=\frac{{{e}^{2}}}{4\pi {{\in }_{0}}}\left( \frac{1}{{{r}^{2}}}+\frac{B}{{{r}^{3}}} \right)\]  and\[mvr=\frac{nh}{2\pi }\Rightarrow v=\frac{nh}{2\pi mr}\]  \[\therefore \]\[m{{\left( \frac{nh}{2\pi mr} \right)}^{2}}\times \frac{1}{r}=\frac{{{e}^{2}}}{4\pi {{\in }_{0}}}\left( \frac{1}{{{r}^{2}}}+\frac{B}{{{r}^{3}}} \right)\] or,\[\frac{1}{{{r}^{2}}}+\frac{B}{{{r}^{3}}}=\frac{m{{n}^{2}}{{h}^{2}}4\pi {{\in }_{0}}}{4{{\pi }^{2}}{{m}^{2}}{{e}^{2}}{{r}^{3}}}\] or  \[\frac{{{a}_{0}}{{n}^{2}}}{{{r}^{3}}}=\frac{1}{{{r}^{2}}}+\frac{B}{{{r}^{3}}}\] \[\left( \because {{a}_{0}}=\frac{{{\in }_{0}}{{h}^{2}}}{m\pi {{e}^{2}}}\text{Given} \right)\]\[\therefore \]\[r={{a}_{0}}{{n}^{2}}-B\]            


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