KVPY Sample Paper KVPY Stream-SX Model Paper-16

  • question_answer
    Temperature at which probability of having an atom in \[n=2\] state is 0.001 will be

    A) \[-\,273K\]

    B) \[300\,K\]

    C) \[1430\,K\]        

    D) \[14300\,K\]

    Correct Answer: D

    Solution :

    Given ratio of number of atoms m state 2 to number of atoms in state 1 is 0.001.
    So,       \[\frac{n\,({{E}_{2}})}{n\,({{E}_{1}})}=\frac{1}{1000}\]
    \[\Rightarrow \]            \[\frac{1}{1000}=\frac{{{N}_{2}}}{{{N}_{1}}}\cdot ({{e}^{-({{E}_{2}}-{{E}_{1}})/kT}})\] ?(i)
    where,\[{{N}_{2}}\]and \[{{N}_{1}}\]are number of possible electron states in \[n=2\] and n =1 quantum states.
    Also, \[{{E}_{2}}\] and \[{{E}_{1}}\] are energies in \[n=2\] and \[n=1\] quantum states.
    Here, \[{{N}_{2}}=8,\]\[{{N}_{1}}=2,\]\[{{E}_{2}}=\frac{{{E}_{1}}}{4}\]and
    \[{{E}_{1}}=-13.6eV\]
    \[k=8.62\times {{10}^{-\,5}}\frac{eV}{K}\]
    Taking log in Eq. (i), we have
    \[T=\frac{1}{k}\cdot \frac{\frac{3}{4}(-{{E}_{1}})}{\log \,(4000)}\]
    \[=\frac{\frac{3}{4}\times 13.6}{8.62\times {{10}^{-5}}\times \log 4000}\]
    \[=1.43\times {{10}^{4}}K\]
    \[=14300K\]


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