JEE Main & Advanced Sample Paper JEE Main Sample Paper-32

  • question_answer
    If \[{{r}_{0}}\] be the radius of first Bohr's orbit of H-atom, the de-Broglie's wavelength of an electron revolving q in third Bohr's orbit will be:

    A) \[2\pi {{r}_{0}}\]       

    B)                    \[4\pi {{r}_{0}}\]

    C) \[6\pi {{r}_{0}}\]   

    D)    \[\pi {{r}_{0}}\]

    Correct Answer: C

    Solution :

    \[mvr\,=\frac{nh}{2\pi }\]                            ?(1)                 \[p=\frac{h}{\lambda }=mv\]                     ?(2) Placing the value of mv from Eq. (2) into Eq. (1) for 3rd orbit                 \[\frac{h}{\lambda }{{r}_{3}}=\frac{3h}{2\pi }\]                 \[\lambda =\frac{2\pi {{r}_{3}}}{3}\]                        \[{{r}_{3}}\,={{n}^{2}}{{r}_{0}}\,=9{{r}_{0}}\]                 So,          \[\lambda =\,\frac{2\pi .9{{r}_{0}}}{3}=6\pi {{r}_{0}}\]


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