Manipal Medical Manipal Medical Solved Paper-2014

  • question_answer
    At what temperature hydrogen molecules will escape from the earth's surface? (Take   mass   of   hydrogen   molecule \[=0.34\times {{10}^{-26}}\]kg,   Boltzmann  constant \[=1.38\times {{10}^{-23}}\] J/K, radius of the earth \[=6.4\times {{10}^{6}}\]m and acceleration due to gravity \[=9.8m/{{s}^{2}}\])

    A) \[10\,K\]                                

    B) \[{{10}^{2}}K\]

    C) \[{{10}^{3}}\,K\]                                 

    D) \[{{10}^{4}}\,K\]

    Correct Answer: D

    Solution :

    The root   mean square velocity of gas \[{{v}_{rms}}=\sqrt{\frac{3KT}{m}}\]                          ?. (i) Escape velocity of gas molecules \[{{v}_{es}}=\sqrt{2g{{R}_{e}}}\]                          ? (ii) At the root mean square velocity of gas, molecule must be equal to the escape velocity. From Eq. (i) and (ii), we get \[\sqrt{\frac{3KT}{m}}=\sqrt{2g{{R}_{e}}}\] \[T=\frac{2g{{R}_{e}}m}{3K}\] \[T=\frac{2\times 9.8\times 6.4\times {{10}^{6}}\times 0.34\times {{10}^{-26}}}{3(1.38\times {{10}^{-23}})}={{10}^{4}}K\]


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