Question

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?

Answer 1

Radius of capillarity r = `2.5 xx 10^-5` m

S = T = `7.8 xx 10^-2 Nm^-1`

g = 9.8 m/s²

h = `(25 cos θ)/(rpg)`

= `(2 xx 7.28 xx 10^-2 cos 0^circ)/(2.5 xx 10^-5 xx 10^3 xx 9.8)`

= `(2 xx 7.28 xx 10^(-2 + 5))/(25 xx 10^3 xx 98)`

h = `(104 xx 10^3)/(175 xx 10^3)`

= `104/175`

= 0.594 m

= 0.6 m

Most of the trees are more than 0.6 m in height. So capillary action alone cannot account for the rise of water in all other trees.