AFMC AFMC Solved Paper-2000

  • question_answer
    At \[{{27}^{0}}C\] temperature the kinetic energy of an ideal gas is E1. If the temperature is increased to 327°C then the kinetic energy will be :

    A) \[\frac{{{E}_{1}}}{\sqrt{2}}\]                                      

    B) \[\sqrt{2}{{E}_{1}}\]

    C) \[2{{E}_{1}}\]                                    

    D) \[\frac{{{E}_{1}}}{2}\]

    Correct Answer: C

    Solution :

                     Let the mass of 1 g molecule of a gas be M, and its mean square velocity be \[{{v}^{2}},\]then kinetic energy of 1 g molecule of gas is \[\frac{1}{2}M{{v}^{2}}=\frac{1}{2}M\left( \frac{3RT}{M} \right)=\frac{3}{2}RT\] There are N-molecules in 1 g molecule of gas. Thus, average kinetic energy of one molecule \[=\frac{(3/2)RT}{N}\] \[=\frac{3}{2}\left( \frac{R}{N} \right)T\] where, (R/N) = k is Boltzmann's constant. \[\therefore \]                  \[KE=\frac{3}{2}kT.\] Given,      \[{{T}_{1}}=27{{\,}^{o}}C=273+27=300\,K\]                \[{{T}_{2}}=327{{\,}^{o}}C=273+327=600\,K\] \[\therefore \]     \[\frac{{{(KE)}_{2}}}{{{(KE)}_{1}}}=\frac{600}{300}=\frac{2}{1}\] \[\Rightarrow \]         \[{{(KE)}_{2}}=2{{(KE)}_{1}}\] \[\Rightarrow \]       \[{{E}_{2}}=2{{E}_{1}}\]


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