**Objective:**

To determine the co-efficient of viscosity of water by poiseull’s capillary flow method

**Theory:**

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,

where,

η = Co-efficient of viscosity

P = Pressure difference between two ends = hρg

g = acceleration due to gravity

where,

h = difference in height between the two arms of the apparatus = (h_{2}-h_{1})

ρ = density of liquid

**Apparatus: **

Viscosity apparatus, Travelling microscope, cathetometer, measuring cylinder, stopwatch.

**Procedure:**

- 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.

**Experimental Results:**

** Vernier constant of the travelling microscope:**

**Measurement of radius of Capillary tube:**

**Calculation:**

**Percentage error:**