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A Question on surface tension

  1. Nov 17, 2016 #1
    1. The problem statement, all variables and given/known data

    Water rises in a capillary tube to certain height such that the upward surface due to surface tension is balanced by 7.5 X 10-4N
    Force due to weight of the liquid. If the surface tension of water is 6 X 10-2Nm-1,the inner circumference of the capillary must be

    2. Relevant equations

    pexcess=2T/rcosθ


    3. The attempt at a solution

    I thought that the force of the excess pressure which causes the movement of liquid must be equal to the weight of the liquid.I know excess pressure is 2T/r (θ=0 for water),but how to find the force of this pressure?Is my approach right?

    Can we just like that multiply 2T/r with πr2because it is not plain liquid but a meniscus?
     
  2. jcsd
  3. Nov 17, 2016 #2
    Yes. The upward force is ##(2\pi r) T##. Think of the surface as a membrane with a tensile force per unit length of T.
     
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