KVPY Sample Paper KVPY Stream-SX Model Paper-26

  • question_answer
    The average life of an excited state of hydrogen atom is of the order of \[{{10}^{-8}}s\]. The number of revolutions made by an electron when it is in state n = 2 and before it suffers a transition to state n= 1, are

    A) \[2.28\times {{10}^{6}}\]

    B) \[22.8\times {{10}^{6}}\]

    C) \[8.23\times {{10}^{6}}\]         

    D) \[2.82\times {{10}^{6}}\]

    Correct Answer: C

    Solution :

    velocity of electron, \[{{V}_{n}}=2.19\times {{10}^{6}}\frac{Z}{n}m{{s}^{-1}}\] (Z=1 for H)
    The distance, travelled by the electron in second Bohr?s orbit in \[{{10}^{-8}}s\]\[=\frac{2.19\times {{10}^{6}}\times 1.0\times {{10}^{-8}}}{2}m=1.095\times {{10}^{-2}}m\]
    The circumference of second orbit \[=2\pi {{r}_{2}}=2\pi \times (0.529\times {{10}^{-10}}\times {{2}^{2}})\]
    \[=13.30\times {{10}^{-10}}m\]
    Number of revolutions \[=\frac{1.95\times {{10}^{-2}}}{13.3\times {{10}^{-10}}}=8.23\times {{10}^{6}}\]


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