Page 114 - Physics - XI

9. Density of the viscous liquid used in the tube = ______ kg m –3
10. Density of experimental viscous liquid, ρ = ______ kg m –3

Table for measurement of time of fall of steel balls
S. No. Diameter of Square of Time taken for covering distance h = ... m Terminal
of spherical balls the radius between rubber bands velocity,
steel of the A and B A and C B and C Mean time, h
ball d (cm) r= d (m) balls t (s) t (s) t = t – t t+ t v= t
2 r (m ) 1 2 3 (s) 1 t= 1 2 3 (s) (ms )
2
2
2
–1
1.
2.
3.

4.
5.

6.

Graph and Calculations
Plot a graph between r and v by taking r along X-axis and v along Y-axis. We will get a straight line.
2
2
Since, the slope of the graph,
BC v Y
tan θ = =
AB r 2 C

2 ( )
Also, coeffi cient of viscosity, η = g
9 v
2
r v (ms –1 )

2 ( ) A θ
It can be rewritten as, η = 9 tan g = ___ poise B

X
2 r slope O r (m )
2
2
Error =
r slope Fig. 5.3: Graph between r and v
2
Standard value of η =___ Nsm –2
Percentage error in η = ___ %
∴ The fi nal value of coeffi cient of viscosity, η = ___ P

Result

1. The graph between terminal velocity (v) and (radius) comes to be a straight line.
2
2. The value of coeffi cient of viscosity for glycerine at temperature T°C is ___ ___ poise.

Precautions
1. The steel ball-bearings should be of small size so that they take longer time to fall through the given
distance.

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