SURFACE TENSION BY CAPILLARY RISE METHOD
To determine surface tension of a liquid by capillary rise method.
A beaker of Water, capillary tube, vernier microscope, two holed rubber stopper, a knitting needle, a short rubber tubing and retort clamp.
The surface tension of the liquid T = hrσg/2 N m-1
T → Surface tension of the liquid (N m–1)
h → height of the liquid in the capillary tube (m)
r → radius of the capillary tube (m)
σ → Density of water (kg m–3) (σ = 1000 kg m–3)
g → Acceleration due to gravity (g = 9.8 m s–2)
· A clean and dry capillary tube is taken and fixed in a stand
· A beaker containing water is placed on an adjustable platform and the capillary tube is dipped inside the beaker so that a little amount of water is raised inside.
· Fix a needle near the capillary tube so that the needle touches the water surface
· A Vernier microscope is focused at the water meniscus level and the corresponding reading is taken after making the cross wire coincidence.
· Vernier microscope is focused to the tip of the needle and again reading is taken and noted.
· The difference between the two readings of the vertical scale gives the height (h) of the liquid raised in the tube.
· Now to find the radius of the tube, lower the height of the support base and remove the beaker, carefully rotate the capillary tube so that the immersed lower end face towards you.
· Focus the tube using Vernier microscope to clearly see the inner walls of the tube.
· Let the vertical cross wire coincide with the left side inner walls of the tube. Note down the reading (L1)
· Turn the microscope screws in horizontal direction to view the right side inner wall of the tube. Note the reading (R1). Thus the radius of the tube can be calculated as ½(L1-R1).
· Finally calculate the surface tension using the given formula.
To measure height of the liquid (h)
Least count of the microscope = ________ × 0.001cm
Radius of the capillary tube
Mean rise of the liquid in the capillary tube h = _________ cm
= _________ m
Diameter of the capillary tube 2r = _________ cm
Radius of the capillary tube r = _________ m
Density of the liquid σ = 1000 kg m-3
Acceleration due to gravity g = 9.8 m s-2
Surface tension T = hrσg/2
Surface tension of the given liquid by capillary rise method T =________N m–1