Water rises to a height h in a capillary tube lowered vertically into water to a depth l (fig) The lower end of the tube is closed, then taken out of water and opened again. The length of the water column remaining in the tube will be-
A] 2h if l>=h and l+h if l<=h
B] h if l>=h and l+h if l<=h
C] 4h if l>=h and l - h if l<=h
D] h/2 if l>=h and l+ h if l<=h

image

[A]

please explain.......

P at A = P at B = P at C = Patm
Upward surface tension force on the liquid column from the tube at the upper surface balances the weight of the liquid column in between points A and B.When the tube is taken out a convex surface is formed at the bottom.Surface tension force on the liquid at this surface also is in upward direction only and has the same magnitude as that on the upper surface and hence can balance the weight of a column of same length(as P at B = P at C, weight of additional length of the liquid column must be balanced by the surface tension force at the lower surface.

Post edited by: niraj001, at: 2008/02/23 11:47