NCERT solution of class 9 chapter matter in our surrounding
Page no. 3
Question
1: Which
of the following are matter?
Chair,
air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume.
Answer
1:
Anything
that occupies space and has mass is called matter. Matter can exist in three
physical states—solid, liquid, and gaseous.
Chair
and almond are forms of matter in the solid state.
Cold
drink is a liquid state of matter.
Air
and smell of perfume are gaseous states of matter.
Question
2:
Give
reasons for the following observation:
The
smell of hot sizzling food reaches you several metres away, but to get the
smell from cold food you have to go close.
Answer
2:
Solids
diffuse at a very slow rate. But, if the temperature of the solid is increased,
then the rate of diffusion of the solid particles into air increases. This is
due to an increase in the kinetic energy of solid particles. Hence, the smell
of hot sizzling food reaches us even at a distance, but to get the smell from
cold food we have to go close.
Question
3:
A
diver is able to cut through water in a swimming pool. Which property of matter
does this observation show?
Answer
3:
The
ability of a diver to cut through water in a swimming pool shows that matter is
made up of particles.
Question
4:
What
are the characteristics of particles of matter?
Answer
4:
The
characteristics of particles of matter are:
Particles
of matter have spaces between them.
Particles
of matter are continuously moving.
Particles
of mater attract each other.
Page no.9
Question 1:
Convert
the following temperature to Celsius scale:
a)
300
K
b)
573
K
Answer
1:
a)
300
K = (300 − 273)°C = 27°C
b)
573
K = (573 − 273)°C = 300°C
Question
2:
What
is the physical state of water at:
a)
250°C
b)
100°C
Answer
2:
a)
Water
at 250°C exists in gaseous state.
b)
At
100°C, water can exist in both liquid and gaseous form. At this temperature,
after getting the heat equal to the latent heat of vaporization, water starts
changing from liquid state to gaseous state.
Question
3:
For
any substance, why does the temperature remain constant during the change of
state?
Answer
3:
During
a change of state, the temperature remains constant. This is because all the
heat supplied to increase the temperature is utilised (as latent heat) in changing
the state by overcoming the forces of attraction between the particles.
Therefore, this heat does not contribute in increasing the temperature of the
substance.
Question
4:
Suggest
a method to liquefy atmospheric gases.
Answer
4:
By
applying pressure and reducing the temperature, atmospheric gases
can be liquefied.
Page
no. 10
Question 1:
Why
does a desert cooler cool better on a hot dry day?
Answer
1:
When
a liquid evaporates, the particles of the liquid absorb energy from the
surroundings to compensate the loss of energy during evaporation. This makes
the surroundings cool.
In
a desert cooler, the water inside it is made to evaporate. This leads to
absorption of energy from the surroundings, thereby cooling the surroundings.
Again, we know that evaporation depends on the amount of water vapour present
in air (humidity). If the amount of water vapour present in air is less, then
evaporation is more. On a hot dry day, the amount of water vapour present in
air is less. Thus, water present inside the desert cooler evaporates more,
thereby cooling the surroundings more.
That
is why a desert cooler cools better on a hot dry day.
Question
2:
How
does water kept in an earthen pot (matka) become cool during summers?
Answer
2:
When
a liquid evaporates, the particles of the liquid absorb energy from the
container to compensate the loss of energy during evaporation. This makes the
remaining water cool.
There
are some pores in an earthen pot through which the liquid inside the pot
evaporates. This evaporation makes the water inside the pot cool. In this way,
water kept in an earthen pot becomes cool during summers.
Question
3:
Why
does our palm feel cold when we put some acetone or petrol or perfume on it?
Answer
3:
When
we put some acetone or petrol or perfume on our palm, it evaporates. During
evaporation, particles of the liquid absorb energy from the surrounding or the
surface of the palm to compensate for the loss of energy, making the
surroundings cool. Hence, our palm feels cold when we put some acetone or
petrol or perfume on it.
Question
4:
Why
are we able to sip hot tea or milk faster from a saucer than a cup?
Answer
4:
A
liquid has a larger surface area in a saucer than in a cup. Thus, it evaporates
faster and cools faster in a saucer than in a cup. For this reason, we are able
to sip hot tea or milk faster from a saucer than a cup.
Question
5:
What
type of clothes should we wear in summers?
Answer
5:
We
should wear cotton clothes in summers. During summers, we sweat more. On the
other hand, cotton is a good absorber of water. Thus, it absorbs sweat from our
body and exposes the liquid to the atmosphere, making evaporation faster.
During this evaporation, particles on the surface of the liquid gain energy
from our body surface, making the body cool
Question 1:
Convert
the following temperatures into the Celsius scale.
(a)
300
K (b) 573 K
Answer
1:
(a)
300
K = 300 – 273 = 27 0C
(b)
573
K = 573 – 273 = 300 0C
Question
2: Convert
the following temperatures into the Kelvin scale.
(a)
25OC
(b) 373OC
Answer
2:
(a)
25OC
= 25 + 273 = 298 K
(b)
373OC
= 373 + 273 = 646 K
Question
3: Give
reasons for the following observations.
(a)
Naphthalene
balls disappear with time without leaving any solid.
(b)
We
can get the smell of perfume sitting several meters away.
Answer
3:
(a)
Naphthalene
shows the property of sublimation. Evaporation of naphthalene takes place
easily and so it disappears during course of time without leaving a solid.
(b)
Perfumes
vaporize very fast and its vapours diffuse into air easily. That is why we can
smell perfume sitting several meters away.
Question
4 Arrange
the following in increasing order of forces of attraction between the particles
– water, sugar, oxygen.
Answer
4:
Oxygen
< Water < Sugar.
Question
5: What
is the physical state of water at —
(a)
25°C
(b) 0°C (c) 100°C?
Answer
5:
(a)
Liquid
(b)
Solid
and Liquid
(c)
Liquid
and Vapours
Question
6: Give
two reasons to justify:
(a)
Water
at room temperature is a liquid.
(b)
An
iron almirah is a solid at room temperature.
Answer
6:
(a)
Water
at room temperature is a liquid because it has fluidity and has definite volume
but no definite shape.
(b)
An
iron almirah is a solid at room temperature because it is rigid and has a
definite shape.
Question 7: Why is ice at 273 K
more effective in cooling than water at the same temperature?
Answer
7:
Ice
at 273 K is less energetic than water. It is because of the difference in the
latent heat of fusion which is present in water at the same temperature in the
form of extra energy.
Question
8: What
produces more severe burns, boiling water or steam?
Answer
8:
Steam
produces more severe burns than boiling water. This is because steam has more
energy than boiling water, present in it in the form of latent heat of
vaporization.
