PHYSICS [3 Mark Question Answer]

The force of attraction between the molecules of a similar kind is called a force of cohesion.
Example:The forces between water molecules.
This force of cohesion keeps the molecules of the substance bind together.
The force of attraction between different types of molecules is called a force of adhesion.
Example: When a glass filled with water is emptied some water particles remain stuck to the glass due to the adhesion between water molecules and glass.

Take 100 ml of water in a measuring cylinder. Add 20 grams of salt in the water gently and stir it well so as to dissolve the salt well in water. It is noticed that the level of water does not change. It shows that the particles of salt occupy spaces between the particles of water.

		Solids	Liquids	Gases
(a)	Compressibility	Not compressible	Negligibly compressible	Highly compressible
(b)	Fluidity	Not possible	Can flow	Can flow
(c)	Rigidity	Highly rigid	Less rigid	Not rigid
(d)	expansion on heating	Low	More than solids	More than liquids

The three states of matter are solids, liquids, and gases.
Solids: A solid has a definite shape and definite volume.
Example: wood, stone, iron, ice, etc
Liquid: A liquid has a definite volume but no definite shape.
Example: water, juice, milk, oil, etc.
Gases: A gas neither has definite shape nor a definite volume.
Example: air, hydrogen, oxygen, water vapour, etc.

Here the molecules are far apart from each other i.e. have the greatest intermolecular distance which results in the weakest intermolecular forces of attraction. The molecules as are not

bound by any strong force move about freely and thus gases do not have a definite shape and also do not have any definite volume.

Here the molecules are less tightly packed as compared to solids and also there is the lesser force of intermolecular attraction. The intermolecular distance is greater than that in the solids. Thus, they do not have a definite shape but acquire the shape of the vessel in which they are contained but have a definite volume at a given temperature.

Here the molecules are very tightly packed that there is no or very less intermolecular space and there is a high intermolecular force of attraction (force of cohesion).
The molecules do not move about their mean position and thus solids have a definite shape and volume.

Take a beaker. Fill it partly with water. Add some lycopodium powder in the beaker containing water. Stir the contents of the beaker with a glass rod. Take out a few drops of this suspension on a glass plate. Place it on the table and illuminate it with a table lamp. Observe the glass plate through a microscope. It is found that the fine particles of lycopodium powder move rapidly in a random manner and their path is zig zag as shown in the figure below.