question_answer 47)

                  The sap in trees, which consists mainly of water in summer, rises in a system of capillaries of radius \[r=2.5\times {{10}^{5}}m\]. The surface tension of sap is \[T=7.28\times {{10}^{-2}}\,N{{m}^{-1}}\] and the angle of contact is \[{{0}^{o}}\]. Does surface tension alone account for the supply of water to the top of all trees?                

Answer:

                  Height through which sap rises is given by                 \[h=\,\frac{2T\,\,\cos \,\,\theta }{r\,\rho \,g}\,\,=\,\frac{2\times \,7.28\,\times \,{{10}^{-2}}\times 1}{2.5\,\,\times {{10}^{-5}}\,\times \,{{10}^{3}}\,\times \,10}\]                 \[(\because \,\cos {{0}^{o}}\,=1)\]                 \[=0.58\,m\]                 No. because many trees are teller than this height.