Page 144 - Physics - XI

Procedure
1. Clean and dry a round bottom fl ask. C Final level

2. Make a small hole in the rubber cork and fi x the given A Initial level
glass capillary tube in it. B level falls up to B
3. Fill the round bottom fl ask completely with glycerine Clamp Capillary tube
so that no air bubbles are present inside the fl ask. stand
Fix the fl ask vertically in the clamp stand as shown Rubber cork
in Fig. 3.1. Trough
4. Fix the rubber cork tightly in the mouth of the fl ask Hot water
so that about 10 to 15 cm of the glass capillary tube Glycerine
is outside the fl ask. Some glycerine will rise in the Round bottom fl ask
capillary tube. Mark the initial level of the glycerine
in the capillary tube as A. Fig. 3.1: Expansion of glycerine

5. Now, place the fl ask containing the glycerine in the trough fi lled with hot water and hold the fl ask in
position with the help of the clamp stand as shown in Fig. 3.1.
6. Observe and record carefully what happens to the level of glycerine in the glass capillary tube after the
fl ask is immersed in hot water bath.

Observations

1. The level of the glycerine in the glass capillary tube falls fi rst. Carefully mark the level B up to which
the glycerine level falls.
2. After occupying the position B, the glycerine level will begin to rise and occupies a stationary position
C (level C is higher than the initial level A).

Result
1. The level of glycerine falls initially on account of the expansion of the fl ask. Thus, fall in the level
of glycerine, i.e. A to B gives the expansion of the fl ask. Thus, when the fl ask expands, its volume
increases and hence some glycerine from the capillary tube falls back into the fl ask so that the level of
glycerine falls to position B.

2. After expansion of the fl ask, expansion of the glycerine takes place so that glycerine level in the
capillary tube occupies a position C. As the expansion of glycerine is more than the expansion of the
glass fl ask so the position C is higher than the initial level A.
3. So, in actual practice glycerine expands in real terms not from level A to level C, but from level B to
level C. Hence, BC gives the real expansion of the glycerine. We have
BC = AC + AB

or Real expansion = Apparent expansion of liquid + Expansion of the vessel

Precautions

1. The glass tube should have a narrow bore.
2. The glycerine should be fi lled completely in the fl ask so that it rises in the capillary tube.

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