Date :
Stoke's Law
Enrolment No. :
AIM : To determine the coefficient of viscosity of the given liquid using Stoke’s method.
APPARATUS : A long glass jar filled with viscous liquid , metre scale , small spherical metal balls ,
micrometer screw gauge , stopwatch.
DIAGRAM :
FORMULA :
𝜂=
2 𝑟 2 𝑔( 𝑑−𝜌 )
9
𝑣
where 𝝶 = coefficient of viscosity , 𝝆 = density of viscous liquid ,
d = density of metal balls , g = acceleration due to gravity ,
r = radius of metal sphere ball , v = terminal velocity
OBSERVATIONS : 1 ) Density of metal ball ( d ) = 7.9 g/cm3
2 ) Density of viscous liquid ( 𝝆 ) = 1.26 g/cm3
3 ) Pitch of the screw ( a ) = 0.05 cm
4 ) Number of divisions on circular scale ( b ) = 50
Stoke’s Law
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5 ) Least count of screw gauge = ( a/b ) = 0.001 cm
6 ) …………………………..Zero error = Z =
cm
7 ) Acceleration due to gravity ( g ) = 980 cm/s2
OBSERVATION TABLE NO. 1 : ( To find radius of metal ball )
Obs.
No.
Main Scale
Reading
( X ) cm
Coinciding
Circular
division ( n )
Circular Scale
Reading
( Y= n x L. C.) cm
Total
Reading
(X+Y+Z)
cm
Mean
Diameter
(X+Y+Z)
( D ) cm
Mean
radius
𝐷
( r = ) cm
1
2
3
OBSERVATION TABLE NO. 2 : ( To find terminal velocity )
Obs.
No.
Distance
between two
mark B and C
i.e. ‘S’ ( cm )
Time taken by
ball to cover
distance BC ( S )
i.e. ‘t’ ( s )
Terminal
velocity
Mean
v=
cm/s
𝑠
𝑡
𝑣
cm/s
1
2
3
4
CALCULATION :
Stoke’s Law
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2
PROCEDURE :
1 ) Measure the diameter of metal ball through three different planes and then
calculate mean radius of it.
2 ) Release a ball gently on the liquid surface at the centre of jar.
3 ) When a ball just crosses a marking ‘A’ , start the stopwatch & when it reaches at
the marking ‘B’ stop the stopwatch. Note down the time taken by ball ‘t’.
4 ) Repeat the same procedure for other 3 – 4 balls.
5 ) Find out the terminal velocity i.e. mean v and finally find out the coefficient of
viscosity by calculation.
RESULT : 1 ) The coefficient of viscosity of the given liquid = ……………………. poise
Stoke’s Law
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