JEE Main & Advanced Physics Fluid Mechanics, Surface Tension & Viscosity / द्रव यांत्रिकी, भूतल तनाव और चिपचिपापन Question Bank Surface Energy

  • question_answer
    8000 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           [EAMCET (Engg.) 2000]

    A) 1 : 10 

    B)                      1 : 15

    C)             1 : 20  

    D)             1 : 25

    Correct Answer: C

    Solution :

                    As volume remains constant \[{{R}^{3}}=8000{{r}^{3}}\]\[\therefore R=20r\] \[\frac{\text{Surface energy of one big drop}}{\text{Surface energy of 8000 small drop}}=\frac{4\pi {{R}^{2}}T}{8000\ 4\pi {{r}^{2}}T}\] \[=\frac{{{R}^{2}}}{8000{{r}^{2}}}=\frac{{{\left( 20r \right)}^{2}}}{8000{{r}^{2}}}=\frac{1}{20}\]


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