LABAPPARA Materials Required

• A long cylindrical glass jar
• Transparent viscous fluid
• Metre scale
• Spherical ball
• Screw gauge
• Vernier calipers
• Stop clock
• Thread

Real Lab Procedure

• Find the least count and zero correction of the given screw guage.
• Find the diameter (d) of the ball using the screw gauge. Now, the radius(r) of ball can be calculated as ; r = d/2
• Clean the glass jar and fill it with the viscous fluid.
• Place a meter scale vertically beside the jar.
• Measure the inner diameter of the jar using a vernier calipers. Hence the inner radius of the jar R can be found.
• Mark two reference points A and B on the jar using two threads. The marking A is made well below the free surface of liquid, so that by the time when the ball reaches A, it would have acquired terminal velocity v.
• Adjust the position the thread B so that the distance between A and B is 60cm.
• The ball of known diameter is dropped gently in the liquid. It falls down in the liquid with accelerated velocity for about one-third of the height. Then it falls with uniform terminal velocity.
• When the ball crosses the point A, start the stop watch and the time taken by the ball to reach the point B is noted.
• If the distance moved by the ball is d and the time taken to travel is t, then velocity,

• Calculate the terminal velocity of the ball, v using the relation,

• Now, the coefficient of viscosity of the liquid can be calculated by using the formula,

• Now, repeat the experiment by changing the diameter of the ball. Calculate the value of r²/ v in each time.
• Plot a graph with r² along X axis and terminal velocity along Y axis. We can calculate the coefficient of viscosity of the liquid by using the slope of the graph.

Procedure

• Select the environment to perform the experiment from the ‘Select the Environment’ drop down list.
• Select the liquid for which the coefficient of viscosity is to be measured, from the ‘Select Viscous Liquid’ drop down list.
• Use the ‘Select jar diameter’ slider to change the diameter of the glass jar.
• Use the ‘Select ball diameter’ slider to change the diameter of the glass ball.
• Change the distance between A and B by dragging the corresponding arrows.
• Drag the glass ball towards the jar and drop it into the liquid in the jar.
• The stop watch runs automatically as the ball reaches the point A, and stops as it leaves the point B.
• The time shown in the stop watch is noted.
• Now, calculations are done as per the observation column and the coefficient of viscosity of the selected liquid can be found out.
• Enable the ‘Show result’ checkbox to view the coefficient of viscosity of the selected liquid.
• Click on the ‘Reset’ button to redo the experiment.

Observations

To find the inner diameter of the glass jar using vernier callipers:

Value of one main scale division            = ……mm

Number of divisions on the vernier          = …….

Least count (L.C.)                                = …….. mm

= ……… cm

Mean diameter of the glass jar, D = ………….. cm

To find the diameter of the sphere using screw gauge:

Pitch of the screw gauge                               = ………. mm

Number of divisions on the circular scale        = ………..

Least count of the screw gauge (L.C.)            =………… mm

Zero correction of the screw gauge (z)            = ………. mm

 To find the terminal velocity of the sphere :

Density of the liquid, ρ                             = ………..kg/m³

Density of the sphere, σ                          = ……….kg/m³

Distance travelled by the sphere, s           = ………. 10^-2 m

Calculations

Radius of the sphere, r                        = d/2

=………. mm

= ………×10^-3 m

Inner radius of the glass jar, R              = D/2

=……….. cm

=……….. ×10^-2 m

Coefficient of viscosity,

= …………. Nsm^-2

Square of radius versus Terminal velocity Graph :

Slope of the graph,

Coefficient of viscosity,

= …………… Nsm^-2

 Result

The coefficient of viscosity of the given liquid, η

By calculation, = ……………..Nsm^-2

From graph,     = ……………..Nsm^-2