Haryana PMT Haryana PMT Solved Paper-2011

  • question_answer
    The root mean square velocity of the molecules               in a sample of helium is \[\frac{5}{7}\]th that of the                 molecules in a simple of hydrogen. If the              temperature of hydrogen sample is \[0{}^\circ C\] then                 that of helium sample is about

    A) \[100{}^\circ C\]

    B) \[273{}^\circ C\]

    C) \[173\text{ }K\]                               

    D) \[0{}^\circ C\]

    Correct Answer: D

    Solution :

    \[\frac{{{v}_{He}}}{v{{H}_{2}}}=\frac{\sqrt{\frac{3R{{T}_{He}}}{{{M}_{He}}}}}{\sqrt{\frac{3RT{{H}_{2}}}{M{{H}_{2}}}}}=\sqrt{\frac{{{M}_{H2}}}{{{M}_{He}}}.\frac{{{T}_{He}}}{{{T}_{H2}}}}\]                 \[\frac{{{v}_{He}}}{{{v}_{H2}}}\sqrt{\frac{2}{4}\times \frac{{{T}_{He}}}{273}}\]                                 \[\frac{5}{7}=\sqrt{\frac{{{T}_{He}}}{2\times 273}}\]                 \[\Rightarrow \]               \[{{T}_{He}}=\frac{25\times 273\times 2}{49}\]                                 \[\approx \text{278K=}{{\text{5}}^{\text{0}}}\text{C}\cong {{\text{0}}^{\text{0}}}\text{C}\]


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