Q16 of 24 Page 75

The sap in trees, which consists mainly of water in summer, rises in a system of capillaries of radius r = 2.5×10-5 m. The surface tension of sap is T = 7.28×10-2 Nm–1 and the angle of contact is 0°. Does surface tension alone account for the supply of water to the top of all trees?

Given:


Radius = r = 2.5×10-5 m


The surface tension of sap = T = 7.28×10-2 Nm-1


angle of contact = 0°


The maximum height h to which sap can rise due to capillary action is given by,


where ρ is density of water.



Since, a lot of trees have heights greater than 0.6m, surface tension does not alone account for the supply of water to the top of all trees.


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