RAJASTHAN ­ PET Rajasthan PET Solved Paper-2002

  • question_answer
    800 identical water drops are combined to form a big drop. Then, the ratio of the final surface energy to the initial surface energy of all the drops together is

    A)  1 : 10            

    B)  1 : 15

    C)  1 : 20            

    D)  1 : 25

    Correct Answer: C

    Solution :

     Surface energy \[W=AT\] \[\frac{{{W}_{1}}}{{{W}_{2}}}=\frac{{{A}_{1}}}{{{A}_{2}}}=\frac{n\times 4\pi {{r}^{2}}}{4\pi {{R}^{2}}}=\frac{n{{r}^{2}}}{{{R}^{2}}}\] But,         \[R=r\times {{n}^{1/3}}\] \[\therefore \] \[\frac{{{W}_{1}}}{{{W}_{2}}}=\frac{n{{r}^{2}}}{{{r}^{2}}{{n}^{2/3}}}={{n}^{1/3}}={{(8000)}^{1/3}}\] \[\frac{{{W}_{2}}}{{{W}_{1}}}=\frac{1}{20}\]


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