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

  • question_answer
    Two capillaries of same length and radii in the ratio 1 : 2 are connected in series. A liquid flows through them in streamlined condition. If the pressure across the two extreme ends of the combination is 1 m of water, the pressure difference across first capillary is

    A)             9.4 m                                        

    B)             4.9 m

    C)             0.49 m                                      

    D)             0.94 m

    Correct Answer: D

    Solution :

                       Given, \[{{l}_{1}}={{l}_{2}}=1,\]and \[\frac{{{r}_{1}}}{{{r}_{2}}}=\frac{1}{2}\]                    \[V=\frac{\pi {{P}_{1}}r_{1}^{4}}{8\eta l}=\frac{\pi {{P}_{2}}r_{2}^{4}}{8\eta l}\]Þ \[\frac{{{P}_{1}}}{{{P}_{2}}}={{\left( \frac{{{r}_{2}}}{{{r}_{1}}} \right)}^{4}}=16\]                    Þ \[{{P}_{1}}=16{{P}_{2}}\]                    Since both tubes are connected  in series, hence pressure difference across combination,                     \[P={{P}_{1}}+{{P}_{2}}\]Þ 1 = \[{{P}_{1}}+\frac{{{P}_{1}}}{16}\] Þ \[{{P}_{1}}=\frac{16}{17}=0.94m\]


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