Page 143 - Physics - XI

Observations

Metal Bending upwards or Metal which is on outer
S. No.
Upper side Lower side downwards side (expands more)

1. Brass Iron Downwards Brass
2. Iron Brass Upwards Brass

Result
1. On heating, the given bi-metallic strip bends in the form of an arc showing that the two metals forming
it expand unequally.

2. It would be observed that the metal (brass) which expands more forms outer side of the bi-metallic
strip.

Precautions

1. The length of bi-metallic strip should be large as compared to its width or thickness.
2. The bi-metallic strip must be riveted at a large number of places.

3. One end of the strip must be rigidly clamped.
4. Heating of whole bi-metallic strip should be uniform.

Sources of Error

1. The rivets may be loose.

2. Heating of strip may not be uniform.

ACTIVITY- 3

Aim

To note the change in level of liquid in a container on heating and interpret the observations.

Apparatus and Materials Required
A round bottom glass fl ask of about 500 mL capacity, a long glass capillary tube of about 20 cm long and
1 mm internal radius, clamp stand, a rubber cork, a trough, glycerine, hot water, stand for holding the fl ask,

a thermometer, and strip of graph paper

Principle/Theory
When a glass fl ask containing a liquid is heated by placing it in a hot water, the level of liquid fi rst falls and
then level of liquid rises. When we heat the liquid, the glass fl ask gets heated up and expands, so the level
of the liquid falls. After this, the liquid starts heating and expands also. Expansion of liquid is more than
that of glass, so fi nally the liquid level rises above the initial level.
A liquid is always contained in a vessel. If we neglect the expansion of the vessel, the expansion of the

liquid is called its apparent expansion. If we also consider the expansion of the vessel, the expansion of
liquid is called real expansion. Hence,
Real expansion of liquid = Expansion of vessel + Apparent expansion of liquid
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