Capillary Rise Method
Capillary Rise Method is suitable for measuring the surface tension and not for interfacial tension When a capillary tube is immersed in a liquid such as water contained in a beaker, the liquid immediately rises up the tube to a certain height Fig. This rise of the liquid in the tube occurs because the force of adhesion between the water molecules and capillary wall is greater than the force of cohesion between the water molecules. By measuring the rise in the capillary, it is possible to determine the surface tension of the liquid.
The liquid in the capillary tube continues to rise till the upward movement is just balanced by the downward force of gravity due to the weight of the liquid. Thus, there are two opposing forces acting against each other, the upward force due to surface tension and the counteracting force due to the weight of the column of liquid in the tube.
Force due to surface tension The surface tension at any point on the circumference of the capillary tube is given by....
γcosθ
γcosθ
where θ is the angle between the surface of the liquid and the capillary wall. Then the total upward forcé along the inside circumference of the capillary is given by....
2πrγ cos θ
where r is the inside radius of the capillary tube
When a liquid such as water wets the surface of the capillary tube, the e is taken as unity. Ther the upward force is given by....
When a liquid such as water wets the surface of the capillary tube, the e is taken as unity. Ther the upward force is given by....
2πrγ
if you have any doubts please let me now