A clean capillary tube of uniform bore is fixed vertically with its lower end dipping into water taken in a beaker. A needle N is also fixed with the capillary tube as shown in the Figure. The tube is raised or lowered until the tip of the needle just touches the water surface.
A travelling microscope M is focused on the meniscus of the water in the capillary tube. The reading R1 corresponding to the lower meniscus is noted. The microscope is lowered and focused on the tip of the needle and the corresponding reading is taken as R2. The difference between R1 and R2 gives the capillary rise h.
The radius of the capillary tube is determined using the travelling microscope. If ρ is the density of water then the surface tension of water is given by T = hrρg /2 where g is the acceleration due to gravity.
