To determine the co-efficient of viscosity of water by poiseull’s capillary flow method
When a liquid flows through a capillary tube of length l and radius r then the volume of liquid flowing per second is given by,
η = Co-efficient of viscosity
P = Pressure difference between two ends = hρg
g = acceleration due to gravity
h = difference in height between the two arms of the apparatus = (h2-h1)
ρ = density of liquid
Viscosity apparatus, Travelling microscope, cathetometer, measuring cylinder, stopwatch.
- Measure the length of the capillary tube with the help of a meter scale.
- Measure the radius of the sample capillary tube with the help of the travelling microscope. Determine the Vernier Constant of the microscope. Place the tube on a stand facing the microscope. Focus the orifice. Take reading of the top, down and right ends of the circular orifice.
- Place the water tank of the viscosity apparatus at a certain level. Allow the water to come out of the tube at a very slow rate (drop by drop). Wait until the water levels at two arms of the manometer take steady values.
- Collect water from the output end in a measuring cylinder for a fixed time, say T = 4 minutes. Measure the volume. From that calculate the volume of water collected per second.
- Change the height of the water tank several times and repeat steps 3 and 4.
- Draw a graph with h in abscissa and V in ordinate. The curve should be a straight line passing through the orifice. If there is a curvature for high values of h, use the linear portion to calculate the slope.
Vernier constant of the travelling microscope:
Measurement of radius of Capillary tube: