Page 108 - Physics - XI

Procedure

(a) Setting the capillary rise tube apparatus
1. Clean the capillary tubes and fl at bottom glass dish in caustic soda and nitric acid and then rinse with
water.

2. Fill the glass dish with water (dust free) and place it on the adjustable stand whose height can be
adjusted. Make its base horizontal by levelling screw.
3. Mount the capillary tubes C whose diameters are ranging from 0.1 mm to 0.5 mm on a glass plate with
the help of rubber bands. Set the glass plate vertically over the dish containing water by holding it in a
clamp stand and adjust the position of the adjustable stand so that the ends of capillary tubes are well
within water as shown in Fig. 4.1.

4. Mount a fi ne needle on the glass plate which is parallel to the capillary tube so that its tip just touches
the water surface as shown in Fig. 4.1.
(b) Measurement of capillary rise

5. Find the least count of a travelling microscope for horizontal and vertical scale and note them.

6. Raise the microscope to a suitable height, keeping its axis horizontal and view the water meniscus in
the fi rst capillary tube (which has maximum rise).
7. After this, with the help of a microscope, let the horizontal cross wire to just touch the central part of
the concave meniscus (It looks convex through the microscope as shown in Fig. 4.2). Take the reading
on the vertical scale of the microscope.

8. Now, move the microscope horizontally and bring it in front of the second capillary tube.
9. Lower the microscope and repeat step 7 for the second capillary tube.

10. Now, repeat steps 8 and 9 for the third capillary tube.
11. Now, move the microscope horizontally and bring it in front of the needle.

R
Horizontal Needle
cross wire d Q
P
S

Fig. 4.2: Inverted meniscus in Fig. 4.3: Needle with its pointed Fig. 4.4: Measurement of diameter
the capillary tube seen end just touches the of the capillary tube
through microscope water surface

12. Now, lower the microscope till the horizontal cross-wire is midway between the pointed end of the
needle and its image in water as shown in Fig. 4.3. Note this reading of the microscope on the vertical
scale. This gives the position of the free surface of the water.
13. Note the temperature of the water with the help of the thermometer.

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