To determine the coefficient of viscosity of a liquid by stokes method
Answers
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.
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