Calculating Capillary Height with Surface Tension: A Question on Homework

[vijayram]

Homework Statement

[/B]
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

Homework Equations

p_excess=2T/rcosθ

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?

 

[Chestermiller]

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.