JEE Main & Advanced AIEEE Solved Paper-2008

  • question_answer
    Suppose an electron is attracted towards the origin by a force \[\frac{k}{r}\] where 'k' is a constant and 'r' is the distance of the electron from the origin. By applying Bohr model to this system, the radius of the \[{{n}^{th}}\] orbital of the electron is found to be \['{{r}_{n}}'\] and the kinetic energy of the electron to be \['{{T}_{n}}'\]. Then which of the following is true?       AIEEE  Solved  Paper-2007

    A) \[{{T}_{n}}\propto \frac{1}{n},\,{{r}_{n}}\propto n\]

    B) \[{{T}_{n}}\propto \frac{1}{n},\,{{r}_{n}}\propto {{n}^{2}}\]

    C) \[{{T}_{n}}\propto \frac{1}{{{n}^{2}}},\,{{r}_{n}}\propto {{n}^{2}}\]

    D) \[{{T}_{n}}\] independent of \[n,\,{{r}_{n}}\propto n\]

    Correct Answer: D

    Solution :

    \[L=\frac{nh}{2\pi }\Rightarrow mv{{r}_{n}}=\frac{nh}{2\pi }\]                 Also, \[\frac{m{{v}^{2}}}{{{r}_{n}}}=\frac{k}{{{r}_{n}}}\Rightarrow m{{v}^{2}}=k\Rightarrow {{T}_{n}}=\frac{1}{2}m{{v}^{2}}=\frac{1}{2}k\],  which is independent of n. \[{{r}_{n}}=\frac{nh}{2\pi mv}=\frac{nh}{2\pi \sqrt{km}}\] \[\therefore \,\,\,{{r}_{n}}\propto n\]


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