Class-6 Science, Chapter-6 Changes Around Us, Solutions and Additional Exercises in line with NCERT book / CBSE Syllabus
Chapter 6
Changes Around Us
Changes Around Us
=========================================================
Additional Exercises
Exercises from
Textbook
Tables from Textbook
Additional Exercises
Choose the correct answer:
1-
Blooming of flowers
is-
a.
Slow change (√)
b.
Fast change
c.
Reversible change
2-
Sharpening a pencil is
a-
a.
Chemical change
b.
Irreversible change
(√)
c.
Slow change
3-
Which of these changes
can be reversed?
a.
Raw egg to boiled egg
b.
Batter to idli
c.
Cold milk to hot milk
(√)
4-
Which of these changes
is irreversible?
a.
Grain to flour (√)
b.
Woolen yarn to knitted
sweater
c.
Stretched rubber band
to its normal size
5-
Change in periods in
your school is-
a.
Non-periodic
b.
Periodic (√)
c.
Reversible
Classify the following changes as reversible
and irreversible changes-
·
Falling of fruit from
tree
·
Maturing of age
·
Glowing of bulb when
switched on and vanishing of light when switched off.
·
Melting of wax on
heating and its solidification on cooling.
·
Burning of paper
leaving behind ashes.
·
Combustion of
fragrance sticks or candles.
Ans- Reversible
changes-
·
Glowing of bulb when
switched on and vanishing of light when switched off.
·
Melting of wax on
heating and its solidification on cooling.
Irreversible Changes-
·
Falling of fruit from
tree
·
Maturing of age
·
Burning of paper
leaving behind ashes.
·
Combustion of
fragrance sticks or candles.
Distinguish between-
(a) Reversible and Irreversible Change
(b) Slow and Fast Change
(c) Periodic and Non-periodic Change
(d) Physical and Chemical Change
Reversible change
|
Irreversible change
|
The changes which are possible in reverse
direction are called reversible changes
|
Changes which are not possible in reverse
direction are called Irreversible changes.
|
Melting of Ice into water is a reversible
change.
|
Falling of fruits from a tree is a
reversible change.
|
Slow change
|
Fast change
|
Changes which may take hours, day- night,
months or years are said to be slow changes.
|
Changes which are instant and occur speedily
are said to be fast changes.
|
Germination of a seed is a slow change.
|
lighting a matchstick is a fast change.
|
Periodic change
|
Non- periodic change
|
Changes which occur after a definite time
interval are called periodic changes.
|
Changes which do not reoccur after a definite
time interval are called non-periodic changes.
|
Periodic changes can be predicted.
|
Non-periodic changes cannot be predicted.
|
Occurrence of days and nights, change in
season and phases of moon are periodic changes
|
Accident, illness, changes due to earthquake
are non periodic changes.
|
Physical change
|
chemical change
|
A temporary change in which only the state,
shape or size of a substance changes and no new substance is formed is termed
as physical change.
|
A
permanent change which results in formation of new substance which differs in
properties from the original substances are called chemical changes.
|
Melting of wax and grinding of sugar are
physical changes.
|
Rusting
of iron and formation of curd from milk are chemical changes
|
Fill in the blanks-
(a) Rusting of iron is irreversible
chemical change. (reversible /
irreversible)
(b) Change in Seasons is a slow and periodic
change. (slow_periodic / fast_ non-periodic)
(c) Ignition of a matchstick is a fast change. (slow/fast)
(d) Melting of ice is a physical and reversible change.(physical_reversible
/ chemical_irreversible)
(e) The human heart - beat is a periodic change. (periodic
/ non-periodic)
(f)
Glowing of an electric bulb is a fast
change. (slow / fast)
Give reasons for the following-
Metal rim is made slightly smaller than wooden
wheel?
Ans- Metal rim is made slightly smaller than the wooden
wheel. On heating, the rim expands and fits onto the wheel. Cold water is then
poured over the rim, which contracts and fits tightly onto the wheel.
Why is the ring in iron tools smaller in size
than the wooden handle?
Ans- The ring in iron tools is slightly
smaller in size than the wooden handle. To fix the handle, the ring is heated
and it becomes slightly larger in size (expands). Now the handle easily fits
into the ring. When the ring cools down it contracts and fits tightly onto the
handle.
Exercises from Textbook
Q. To walk through a
waterlogged area, you usually shorten the length of your dress by folding
it. Can this change be reversed?
Ans- Yes, this change
can be reversed.
Q. You accidentally
dropped your favorite toy and broke it.
This is a change you did not want.
Can this stage be reversed?
Ans- No, this change
can not be reversed.
Some changes are
listed in the following table. For each
change, write in the blank column, whether the change can be reversed or not.
S.No.
|
Change
|
can be reversed (Yes\No)
|
1
|
The sawing of a piece of wood
|
No
|
2
|
The melting of ice candy
|
Yes
|
3
|
dissolving sugar in water
|
Yes
|
4
|
The cooking of food
|
No
|
5
|
The ripening of mango
|
No
|
6
|
Souring of milk
|
No
|
Q. A drawing sheet
changes when you draw a picture on it. Can you reverse this change?
Ans- No, the change
cannot be reversed after drawing on a sheet. However, if drawing is done with a
pencil, we can rub it.
Q. Give examples to
explain the difference between changes that can or can not be reversed.
Ans- Following
examples explain the difference between reversible and irreversible change:
Reversible change
|
Irreversible change
|
Blow a balloon and
see the change in its shape and size àThis change can be reversed by escaping air
from balloon.
|
Blow a balloon and
see the change in its shape and size à This change can not be reversed if we burst
the balloon by pricking it.
|
Take a sheet of
paper and make an aeroplane. à This change can be reversed by unfolding
paper.
|
On the same sheet of
paper if we draw and cut the outline of aeroplane. à This change can not be reversed.
|
Roll out a chapatti
from a ball of dough à we can change it into a ball of dough
again.
|
If we bake a roti on
tawa à we can not make the ball of dough again.
|
Q. A thick coating of
a paste of Plaster of Paris (POP) is applied over the bandage on a fractured
bone. It becomes hard on drying to keep the fractured bone immobilized. Can the
change in POP be reversed.
Ans- No, the change in
POP can not be reversed as it becomes hard on drying.
Q. A bag of cement
lying in the open gets wet due to rain during the night. The next day the sun
shines brightly. Do you think the changes, which have occurred in the cement,
could be reversed?
Ans- No, this change
can not be reversed as the cement hardens on drying after being wet.
Tables from Textbook
Table 6.1
some common changes
Change
|
can be
reversed
|
Raw egg boiled egg
|
no
|
Batter to Idli
|
no
|
Wet clothes to dry clothes
|
yes
|
Woolen yarn to knitted sweater
|
yes
|
Grain to its flour
|
no
|
Cold milk to hot milk
|
yes
|
Straight string to a coiled string
|
yes
|
Bud to flower
|
no
|
Milk to paneer
|
no
|
Cow dung to biogas
|
no
|
Stretched rubber band to its normal size
|
yes
|
Ice cream to molten ice cream
|
yes
|
Activity / Project
1.
Take a lemon, a paintbrush and a piece of paper. Cut the lemon
and squeeze out its juice in a cup. Dip the brush in the lemon juice and write
a message on the paper. Let the paper dry and you find that the letters of your
message become invisible. Now, press the paper with hot iron or vomit by
holding it above the flame of a candle (take care that it does not catch fire).
As paper gets warm, invisible letters change into dark brown colour. Identify
the changes that can be reversed.
2.
Observe preparation of dishes at your home. Identify two changes
that can be reversed.
3.
Record for one year of the seasonal changes in vegetables,
clothing, nature and events around you. Identify the changes that can or cannot
be reversed.
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