JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2011

  • question_answer
        A soap bubble oscillates with time period T, which in turn depends on the pressure p, density\[\rho \]and surface tension o. Which of the following correctly represents the expression for\[{{T}^{2}}\]?

    A)  \[\frac{\rho {{\sigma }^{2}}}{{{p}^{3}}}\]                             

    B)  \[\frac{\rho {{\sigma }^{3}}}{\sigma }\]

    C)  \[\frac{{{\rho }^{3}}\sigma }{\rho }\]                     

    D)  \[\frac{\rho }{{{p}^{3}}\sigma }\]

    Correct Answer: A

    Solution :

                    Here, \[{{T}^{2}}={{p}^{a}}{{\rho }^{b}}{{\sigma }^{c}}\]                                                ?.(i) Putting the dimensions of R.H.S. quantities, we get                 \[={{[M{{L}^{-1}}{{T}^{-2}}]}^{a}}{{[M{{L}^{-3}}]}^{b}}{{[M{{T}^{-2}}]}^{c}}\]                 \[=[{{M}^{a+b+c}}{{L}^{-a-3b}}{{T}^{-2a-2c}}]\] Hence, \[a+b+c=0\]                 \[-a-3b=0\] and         \[-2a-2c=2\] On solving, we get \[a=-3,\text{ }b=1\]and\[c=2\] So, after putting the values of a, b and c in Eq. (i), we get  \[{{T}^{2}}=\frac{\rho {{\sigma }^{2}}}{{{p}^{3}}}\]


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