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Question 1

Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume. 

The following are the Matter : Chair, air, almonds, cold drink, smell of perfume.

Question 2

Give reasons for the following observation:
The smell of hot sizzling food reaches you several metres away, but to get smell from cold food you have to go close.

The smell of hot sizzling food reaches us several metres away because food particles diffuse faster in air when hot and we smell it no time whereas cold food particles would take a very long time to diffuse and we have to go close to have a smell of it.

Question 3

A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

This shows that the particles of matter have space between them. This space is the maximum in the gases and the minimum in liquid. Thus, one cannot cut through a solid easily but a diver is able to cut easily through water in a swimming pool.

Question 4

What are the characteristics of the particles of matter?


The characteristics of the particles of matter are as follows:

Particles have matter have space between them.

They are continuously moving and thus possess kinetic energy.

They attract each other.

They can diffuse into one another.

Question 5

The mass per unit volume of a substance is called density. Arrange the following in order of increasing density- air, exhaust from chimneys, honey , water, chalk, cotton and iron.

The increasing order of density of the above is as follows
Air< exhaust from chimneys< cotton< water < honey< chalk < iron

Question 6

Tabulate the differences in the characteristics of states of matter
b. Comment upon the following:
rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density. 

Distinction between the three States of Matter on the basis of Particle Model
The main points of distinction between the solids, liquids and gases are given below:

S.NO Property Solid Liquid Gases
1 Shape They Have definite shape They do not have definite shape They do not have definite shape
2 Volume They have definite volume They do not have definite volume  They do not have definite volume
3 Density They have high density Liquids have less density than solids. Liquids have least density.
4 Kinetic energy of particles. Least More than solids Maximum
5 Compressibility Negligible Low High

It is the property of matter to resist the change of its shape.

It is the property of matter in which its volume is decreased by applying force.
It is the ability of matter to flow.

filling a gas container:- 
On filling a gas takes the shape of the container.

Having definite boundaries.

kinetic energy:-
It is the energy possessed by the particles of matter due to its motion.

It is the ratio of mass with per unit volume.

Question 7

Give reasons
a. A gas fills completely the vessel in which it is kept.
b. A gas exerts pressure on the walls of the container.
c. A wooden table should be called a solid.
d. We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert. 

There is no force of attraction between gas particles. So they are free to move and occupy all the space available to them. So it fills completely the vessel in which it is kept.
b. The gas particles are constantly moving randomly at high speeds in all directions and in this process they collide with each other and also walls of the container. The impact or force of the motion.
c. When wooden table is subjected to outside force it maintains its shape. So it is a solid.
d. Gas particles in the air are far apart. These have no force of attraction among themselves. But in a solid block of wood, the particles of wood are strongly held together and tremendous force needs to be applied to make them apart.

Question 8

Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why?

Ice which is a solid has vacant spaces between water molecules thus making ice lighter than water. So ice is lighter than water it floats on water.

Question 9

Convert the following temperature to Celsius scale.
a. 300K b. 573 K

a.300K = 300- 273 = 27oC
b. 573K = 573- 273 =300 o C

Question 10

What is the physical state of water at
a. 250o C
b. 100oC

a. At 250 o C the water becomes vapour. So water exists in vapour state at 250oC.
b.At 100 o C the water starts boiling and there exists an equilibrium between vapour state and liquid state.

Question 11

For any substance, why does the temperature remain constant during the change of state?

While changing the state of matter the heat given to the matter is used up in changing the state of matter. This is called latent heat.

Question 12

Suggest a method to liquefy atmospheric gases.

Atmospheric gases can be liquefied if a high pressure is applied at some low temperature.

Question 13

Why does a desert cooler cool better on a hot dry day?

There is a high temperature and low humidity on a hot dry day. Both these factors are responsible for increasing evaporation. This also means better cooling.

Question 14

How does the water kept in an earthern pot (matka) become cool during summers?

Earthern pot becomes cool during summer particularly in a hot day because water evaporation from the pot becomes easier. Since evaporation causes cooling matka becomes cool during summers.

Question 15

Why does our palm feel cold when we put some acetone or petrol or perfume on it?

Both acetone and perfume are volatile liquids. When kept on palm, they can absorb enough energy from the palm or surroundings and evaporate and leave the palm cool.

Question 16

Why are we able to sip hot tea or milk faster from a saucer rather than a cup?

The hot tea or milk when poured in saucer cover larger surface area on a saucer and resulting in increase of evaporation. So the tea or milk cool faster on a saucer and we can sip it more comfortably.

Question 17

What types of clothes should we wear during summer season?

We should wear cotton clothes during summer season because we perspire more to maintain the temperature of our body.

Question 18

Convert the following temperatures to Celsium scale.
(a) 300K (b) 573 K


(a) 300K =300 -273 = 27o C
(b) 573K = 573-273 = 300O C

Question 19

Convert the following temperatures to Kelvin scale.
a. 25o C   b. 373o C

a. 25oC = 25 + 273 = 298K
b. 373o C = 373 + 273 = 646 K

Question 20

Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any
(b) We can get the smell of perfume sitting several metres away.

a. Naphthalene balls sublimes from solid state to vapour state directly. So it disappears without leaving any solid.
b. Perfumes has high degree of vaporization and its vapour diffuse into air easily. So we can smell of perfume sitting several metres away.

Question 21

What is the physical state of water at—
(a) 25°C(b) 0°C (c) 
100°C ? 

The physical state of water at
25oC is liquid
0°C is solid
100°C is gas

Question 22

Give two reasons to justify—
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.

Water at room temperature is a liquid because it has fluidity and assumes the shape of the containing vessel.
b. An almirah is a solid because it is rigid and has a fixed shape.

Question 23

Why is ice at 273 K more effective in cooling than water at the same temperature? 

At 273 K ice is less energetic than water the difference being the latent heat of fusion.

Question 24

What produces more severe burns, boiling water or steam?

Steam is more energetic than boiling water so it produces more severe burns.

Question 25

Name A,B,C,D,E and F in the following diagram showing change  in its state .

A→Fusion or melting , B→Vaporization or boiling, C→Condensation, D→Solidification, E→Sublimation(Step 1), F→Sublimation(Step2).

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