Page 145 - Physics - XI

3. No air bubbles should be present inside the fl ask.

4. There should be no leakage of glycerine from anywhere.

Sources of Error

1. Heating of the glycerine may not be uniform.
2. Temperature of the hot water bath may not be steady.

ACTIVITY - 4

Aim

To study the eff ect of detergent on surface tension of water by observing capillary rise.

Apparatus and Materials Required

A capillary tube of uniform bore, beaker of 250 mL, 15/30 plastic scale, clamp stand, distilled water, and
small quantity of solid/liquid detergent

Principle/Theory
When we add a small quantity of detergent powder or liquid detergent
in distilled water, the surface tension of solution is found less than Rubber Capillary
tube
that of distilled water. For a given capillary tube, the rise of liquid in band

the capillary tube is directly proportional to the surface tension of Scale
r rdg rhdg Clamp h 2
the liquid T h . . Therefore, when we add stand

32cos 2cos h
detergent to water, its surface tension decreases. More is the decrease Rubber
band h 1
in surface tension, less would be the rise of detergent solution in the
capillary tube. Hence, if we take equally concentrated solutions of Water
diff erent detergents in water, rise of solution in the capillaries of the
same bore would be the least for the best detergent and maximum
for the worst detergent. Fig. 4.1: Experimental set up to
study capillary rise in water
Procedure
1. Clean and rinse a capillary tube of uniform bore with distilled water. The capillary tube must be dry
and free from grease, oil, etc. and it should be open from both the ends. Clean and rinse the beaker with
water.

2. Pour water to fi ll the beaker up to half.
3. Using rubber bands, mount the plastic scale with the capillary tube.
4. Now, with the help of a clamp stand, hold the scale with capillary in vertical position.

5. The half-fi lled beaker is placed below the lower end of the scale and gradually lower down the scale
till its lower end gets immersed below the surface of water in the beaker.

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