VISCOSITY OF A LIQUID BY STOKE’S METHOD
To determine the co-efficient of viscosity of the given liquid by stoke’s method
A long cylindrical glass jar, highly viscous liquid, metre scale, spherical ball, stop clock, thread.
η - Coefficient of viscosity of liquid (N s m–2)
r → radius of spherical ball ( m )
δ→ density of the steel sphere ( kg m–3 )
σ→ density of the liquid ( kg m–3 )
g → acceleration due to gravity (9.8 m s–2 )
V → mean terminal velocity ( m s–1 )
· A long cylindrical glass jar with markings is taken.
· Fill the glass jar with the given experimental liquid.
· Two points A and B are marked on the jar. The mark A is made well below the surface of the liquid so that when the ball reaches A it would have acquired terminal velocity V.
· The radius of the metal spherical ball is determined using screw gauge.
· The spherical ball is dropped gently into the liquid.
· Start the stop clock when the ball crosses the point A. Stop the clock when the ball reaches B.
· Note the distance between A and B and use it to calculate terminal velocity.
· Now repeat the experiment for different distances between A and B. Make sure that the point A is below the terminal stage.
To find Terminal Velocity:
Density of the spherical ball δ = ________ kg m−3
Density of the given liquid σ = ________ kg m−3
Coefficient of viscosity of the liquid η = 2r2g(δ −σ) / 9V = = ________ N s m–2
The coefficient of viscosity of the given liquid by stoke’s method η = ________ Nsm–2