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

  • question_answer
    One thousand small water drops of equal radii combine to form a big drop. The ratio of final surface energy to the total initial surface energy is                 [MP PET 1997; KCET 1999]

    A) 1000 : 1          

    B)              1 : 1000

    C)             10 : 1  

    D)             1 : 10

    Correct Answer: D

    Solution :

                    As volume remain constant therefore \[R={{n}^{1/3}}r\] \[\frac{\text{surface energy of one big drop}}{\text{surface energy of }n\text{ drop}}=\frac{4\pi {{R}^{2}}T}{n\times 4\pi {{r}^{2}}T}\]             \[\frac{{{R}^{2}}}{n{{r}^{2}}}=\frac{{{n}^{2/3}}{{r}^{2}}}{n{{r}^{2}}}\]= \[\frac{1}{{{n}^{1/3}}}=\frac{1}{{{(1000)}^{1/3}}}=\frac{1}{10}\]


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