JEE Main & Advanced Physics Wave Mechanics Question Bank Critical Thinking

  • question_answer
    Oxygen is 16 times heavier than hydrogen. Equal volumes of hydrogen and oxygen are mixed. The ratio of speed of sound in the mixture to that in hydrogen is         [KCET 2004]

    A)            \[\sqrt{\frac{1}{8}}\]        

    B)            \[\sqrt{\frac{32}{17}}\]

    C)            \[\sqrt{8}\]                           

    D)            \[\sqrt{\frac{2}{17}}\]

    Correct Answer: A

    Solution :

                Density of mixture \[={{\rho }_{mix}}=\frac{{{V}_{{{O}_{2}}}}{{\rho }_{{{O}_{2}}}}+{{V}_{{{H}_{2}}}}{{\rho }_{{{H}_{2}}}}}{{{V}_{{{O}_{2}}}}+{{V}_{{{H}_{2}}}}}\]                    \[=\frac{V\left( {{\rho }_{{{O}_{2}}}}+{{\rho }_{{{H}_{2}}}} \right)}{2\,V}=\frac{{{\rho }_{{{O}_{2}}}}+{{\rho }_{{{H}_{2}}}}}{2}\](since\[{{V}_{{{O}_{2}}}}={{V}_{{{H}_{2}}}}=V\])                    \[=\frac{{{\rho }_{{{H}_{2}}}}+16{{\rho }_{{{H}_{2}}}}}{2}=8.5{{\rho }_{{{H}_{2}}}}\]Þ \[v\propto \frac{1}{\sqrt{\rho }}\]                    Þ\[\frac{{{V}_{mix}}}{{{V}_{{{H}_{2}}}}}=\sqrt{\frac{{{\rho }_{{{H}_{2}}}}}{{{\rho }_{mxn}}}}=\sqrt{\frac{{{\rho }_{{{H}_{2}}}}}{8.5{{\rho }_{{{H}_{2}}}}}}\approx \sqrt{\frac{1}{8}}\]


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