JEE Main & Advanced Physics Fluid Mechanics, Surface Tension & Viscosity / द्रव यांत्रिकी, भूतल तनाव और चिपचिपापन Question Bank Self Evaluation Test - Mechanical Properties of Fluids

  • question_answer
    Two capillary of length L and 2L and of radius R and 2R are connected in series. The net rate of flow of fluid through them will be (given rate to the flow through single capillary, \[X=\frac{\pi P{{R}^{4}}}{8\eta L}\])

    A) \[\frac{8}{9}X\]

    B) \[\frac{9}{8}X\]

    C) \[\frac{5}{7}X\]

    D) \[\frac{7}{5}X\]  

    Correct Answer: A

    Solution :

    [a] Fluid resistance is given by \[R=\frac{8\eta L}{\pi {{r}^{4}}}\] When two capillary tubes of same size are joined in series, then equivalent fluid resistance is \[{{R}_{S}}=\frac{8\eta L}{\pi {{R}^{4}}}+\frac{8\eta \times 2L}{\pi {{(2R)}^{4}}}=\left( \frac{8\eta L}{\pi {{R}^{4}}} \right)\times \frac{9}{8}\] \[Rate\,of\,flow=\frac{P}{{{R}_{S}}}=\frac{\pi P{{R}^{4}}}{8\eta L}\times \frac{8}{9}=\frac{8}{9}X\left[ as\,X=\frac{\pi P{{R}^{4}}}{8\eta L} \right]\]


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