Page 109 - Physics - XI

(c) Measurement of internal diameter of capillary tube

14. Place the capillary tube horizontally on the adjustable stand.
15. Focus the microscope on a fi ne hole of the tube and measure its internal diameter in two mutually
perpendicular directions PQ and RS as shown in Fig. 4.5. Repeat this procedure to fi nd out the internal
diameters of the other two capillary tubes.

16. Record all the observations in the observation tables.

Observations

Least count of the travelling microscope = L.C. = ______ cm

Table for calculation of height of the water risen in the capillary tubes

S. No. of Reading of water meniscus Reading of the tip of the needle h = h – h
Capillary 1 2
tube Main scale No. of V.S. Total Main No. of V.S. Total reading
reading division reading scale division h =
2
A coinciding h = (A + n × reading coinciding (A′ + n′ ×
1
'n' L.C.) A′ n′ L.C. )
(cm) (cm) (cm) (cm) (cm)

1.
2.

3.

Table for calculation of internal diameter of the capillary tubes

S. No. of Microscope reading (cm) Horizontal Vertical Mean Mean radius
Capillary diameter diameter diameter d
tube P Q R S d = PQ d = RS d+ d r = 2
1 2 d = 1 2
2 (cm)
(cm) (cm) (cm)

1.
2.

3.

Temperature of the water = t°C = ______ °C

Density of the water at temperature t°C = ρ = ______ g cm –3

Calculations
We have the relation

r
rh g

T = 3 = ______ dynes/cm = ______ × 10 Nm –1
–3
2
Now, substitute the values of h and r for each capillary and calculate the value of T.

Mean value of T = T + 1 T + 2 T 3 = ______ dynes/cm = ______ Nm –1
3
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