Changes Around Us

Punjab State Board PSEB 6th Class Science Book Solutions Changes Around Us Textbook Exercise Questions and Answers.

PSEB Solutions for Class 6 Science Chapter 6 Changes Around Us

Science Guide for Class 6 PSEB Changes Around Us Intext Questions and Answers

Think and Answer (Textbook Page No. 53)

Question 1.
Before preparing roti your mother makes a ball from the dough. Can the ball be reversed into dough?
Answer:
Yes, the ball can be reversed into the dough.

Question 2.
You make a toy boat from a piece of paper. Can you obtain back the paper in original form?
Answer:
Yes, we can obtain back the paper in original form.

Think and Answer (Textbook Page No. 54)

Question 1.
Observe the height of students of class 5th and of class 8th. Is the change in height a reversible or irreversible change ?
Answer:
The change in height is an irreversible change.

Question 2.
Is burning of candle reversible or irreversible change ?
Answer:
The burning of candle is an irreversible change.

Think and Answer (Textbook Page No. 55)

Question 1.
Which type of change is involved in tearing of paper ?
Answer:
Physical change.

Question 2.
Which type of change is involved in melting of ice to water ?
Answer:
Physical change.

Think and Answer (Textbook Page No. 56)

Question 1.
What type of change is observed in formation of paneer from milk ?
Answer:
Irreversible change.

Question 2.
Name the change involved in formation of wax from burning candles.
Answer:
Physical change.

Think and Answer (Textbook Page No. 57)

Question 1.
Have you seen Bunsen Burner in the shop of goldsmith? What is its purpose there ?
Answer:
It is used for melting of gold.

Question 2.
When you put clinical thermometer in your mouth, why do Mercury in the thermometer rises and why it falls down when you take it out ? (noted that Mercury is a metal which is liquid at room temperature)
Answer:
Metals expand on heating and contract on cooling. When we put clinical thermometer in our mouth due to higher temperature inside the mouth the mercury in the thermometer rises. When we take out the mercury falls because the outside temperature is lower than the temperature of the mouth.

PSEB 6th Class Science Guide Changes Around Us Textbook Questions and Answers

1. Fill in the Blanks:

(a) A new substance is always formed in …………….. change.
Answer:
chemical

(b) Melting of ice is ……………… and ……………… change.
Answer:
physical, reversible

(c) Burning of paper is ……………… change.
Answer:
chemical/irreversible

(d) On heating, metals ………………
Answer:
expand

(e) Change that is repeated after regular interval of time is known as …………….
Answer:
periodic change

Write True or False:

(a) Converting milk into paneer is a reversible change.
Answer:
False

(b) Rusting of iron is a slow change.
Answer:
True

(c) Metals contract on heating.
Answer:
False

(d) Melting of snow from mountains is a natural change.
Answer:
True

(e) Bursting of crackers is a fast change.
Answer:
True

3. Match the Column A with Column B:

Column A	Column B
1. Freezing of water	(a) Non-periodic
2. Milk to curd	(b) Physical and reversible
3. Burning of matchstick	(c) Periodic
4. Earthquake	(d) Fast
5. Change of season	(e) Chemical.

Answer:

Column A	Column B
1. Freezing of water	(b) Physical and reversible
2. Milk to curd	(e) Chemical.
3. Burning of matchstick	(d) Fast
4. Earthquake	(a) Non-periodic
5. Change of season	(c) Periodic.

4. Choose the Correct Answer:

Question (i)
Cooking of food is which type of change ?
(a) Physical
(b) Fast
(c) Reversible
(d) Irreversible.
Answer:
(d) Irreversible.

Question (ii)
Which of the following is change a non-periodic ?
(a) Heart beat
(b) Earthquake
(c) Occurence of day and night
(d) Motion of pendulum.
Answer:
(b) Earthquake

Question (iii)
Which of the following expand on heating ?
(a) Wood
(b) Paper
(c) Metal
(d) Cloth.
Answer:
(c) Metal

Question (iv)
Rusting of iron is which type of change ?
(a) Reversible
(b) Slow
(c) Periodic
(d) Fast.
Answer:
(b) Slow

Question (v)
Growth in plants and animals is which type of change :
(a) Slow
(b) Reversible
(c) Chemical
(d) Periodic.
Answer:
(a) Slow

5. Very Short Answer Type Questions:

Question (i)
What are changes ?
Answer:
Change is an act by which a thing becomes different from its previous one.

Question (ii)
Define slow and fast changes with examples.
Answer:
Slow changes are those which takes more time to happen. For example, growing of tree, a baby becoming adult, etc.
Fast changes are those that happen very fast. For example, burning of match stick, bursting of crackers, etc.

Question (iii)
Give two examples of reversible change.
Answer:
Melting of ice and expansion of metals on heating.

Question (iv)
Why, the iron rim is slightly smaller in diameter than the wooden wheels ?
Answer:
The metal rim used is slightly smaller in diameter than the wooden wheels because
on heating the rim expands and can easily lie on the wheels. When the rim cools, it contracts and fits tightly onto the wheel.

Question (v)
Give two examples of chemical change.
Answer:
Converting milk into cheese and curd, cooking of vegetables.

6. Short Answer Type Questions:

Question (i)
Give differences between periodic and non-periodic changes with examples.
Answer:
Periodic change. Changes that are repeated after regular interval of time are called periodic changes.
Examples are change of day and night, swinging of pendulum of clock, beating of heart, change of seasons.

Non-periodic change. Changes that are not repeated after regular interval of time are called non-periodic changes.
Examples are occurrence of earthquakes, occurrence of rain, etc.

Question (ii)
Give differences between reversible and irreversible changes with examples.
Answer:
Reversible change. When a change in a substance can be reversed by changing the conditions it is said to be a reversible change.
Examples are melting of ice, evaporation of water, etc.

Irreversible Change. If a substance after change cannot be brought back to its original state then the change is said to be an irreversible change.
Examples are cooking of food, converting milk into cheese and curd, etc.

Question (iii)
Why a candle in reduces in size on burning ?
Answer:
On burning, some of the wax melts and some of it changes to carbon dioxide and water. Due to these changes the size of the candle reduces on burning.

Question (iv)
Give differentce between physical and chemical changes with examples.
Answer:
Physical Change.
Physical change is a temporary change in which no new substance is formed and chemical composition of the original substance remains the same. During this change colour, shape, size, state, etc. may change. It is a reversible change. Melting of ice, blowing of balloon, stretching of rubber, tearing of paper, folding a paper, etc. are some of the examples of physical changes.

Chemical changes.
Any change which is permanent, in which new substances are formed whose physical and chemical properties are completely different from those of the original substance is called a chemical change. Chemical changes are irreversible in nature.
Ripening of mango, cooking of food, converting milk to paneer, growth of plants, etc. are some of the examples of chemical changes.

7. Long Answer Type Question:

Question (i)
What is expansion ? Define thermal expansion ? Explain with two examples.
Answer:
Expansion. It can be defined as the increase in the dimension of a body when
subjected to high temperature and high pressure. For example blowing of balloon, stretching of spring.
When expansion is due to increase in temperature it is called as thermal expansion.
We can explain this with the help of many examples.

• When we put clinical thermometer in our mouth, the level of mercury increases. This is because mercury is a metal and metals expand on heating.
• A metal ball which can pass through a ring on heating becomes larger in size and cannot pass through the same ring.

PSEB Solutions for Class 6 Science Changes Around Us Important Questions and Answers

Multiple Choice Questions:

Question 1.
Balloon bursts:
(a) when we blow it.
(b) when we put water into it.
(c) when it is pricked.
(d) all the above.
Answer:
(c) when it is pricked.

Question 2.
Water changes into vapours:
(a) on cooling
(b) on heating
(c) by both (i) and (ii)
(d) none.
Answer:
(b) on heating

Question 3.
Cow dung changes to biogas. It is an example of:
(a) Reversible change
(b) Irreversible change
(c) both
(d) none.
Answer:
(b) Irreversible change

Fill in the Blanks:

(a) When a fully blown balloon is pricked, it ………………
Answer:
bursts

(b) Pencil changes its …………….. and size with repeated use.
Answer:
shape

(c) Iron is heated till it becomes red hot and soft to be ……………… into a desired shape.
Answer:
beaten

(d) Ice ……………. when it is heated.
Answer:
melts

(e) The change of milk to paneer is a ……………….. change.
Answer:
irreversible

(f) When two substances are mixed together, they undergo …………… only on heating.
Answer:
changes

Write (T) against true and (F) against false statement:

(a) Salt cannot be separated from its solution.
Answer:
False

(b) Flowers bloom and wither away.
Answer:
True

(c) A baked roti is an example of irreversible change.
Answer:
True

(d) When a candle bums, its size decreases.
Answer:
True

(e) Iron expands on heating.
Answer:
True

(f) Many changes occur due to some magical power.
False

Very Short Answer Type Questions

Question 1.
What type of a change is cooking of food ?
Answer:
Irreversible change.

Question 2.
What happens when we blow a balloon ?
Answer:
It expands and grows in size.

Question 3.
Can rolled out roti be reversed to dough ?
Answer:
Yes.

Question 4.
Give an example of irreversible change.
Answer:
Cutting of paper into bits.

Question 5.
When candle burns which change takes place ?
Answer:
Irreversible change.

Question 6.
Define solution.
Answer:
Solution. A clear homogeneous mixture of solid and liquid is called solution. For example, salt dissolved in water.

Question 7.
What type of change is a change of climate ?
Answer:
Slow change.

Question 8.
What type of change is a cooking of food ?
Answer:
Irreversible change.

Question 9.
What type of change is rusting of iron ?
Answer:
Irreversible change. During rusting a reddish brown substance iron oxide is formed.

Question 10.
State whether burning of a piece of paper is a reversible or an irreversible change.
Answer:
Burning of a piece of paper is an irreversible change.

Question 11.
Is printing a reversible or an irreversible change ?
Answer:
Printing is an irreversible change.

Question 12.
Can we say that ironing of a cloth is a reversible change ?
Answer:
Yes, ironing of a cloth is a reversible change.

Short Answer Type Questions

Question 1.
Name the various changes taking place in nature.
Answer:
Changes in nature.

1. Falling of leaves from trees.
2. Blooming of flowers.
3. Ripening of fruits.
4. Drying of wet clothes.
5. Growth of nails and hair.

Question 2.
Give examples of changes which can be reversed easily.
Answer:
Reversible changes.

1. Blowing air into a balloon.
2. Rolling out a roti.
3. Folding paper toys.
4. Melting of ice.

Question 3.
Write few changes which cannot be reversed at all.
Answer:
Irreversible Changes.

1. Growth of a person.
2. Baked roti.
3. Baked earthen pot in oven.
4. Burning of candle.

Question 4.
Why is curd formation an irreversible change ?
Answer:
Curd formation is done by adding little curd to warm milk. In this method, the milk sets into curd and curd cannot be churned back into milk. So curd formation is an irreversible change.

Question 5.
Classify the following changes :
(i) Heating black material (tar) for repairing a road.
(ii) Melting of ice cubes.
(iii) Growth of hair.
(iv) Heating wax.
(v) Burning of candle.
(vi) Burning of incense stick.
Answer:
(i) Reversible change.
(ii) Reversible Change.
(iii) Irreversible Change.
(iv) Reversible Change.
(v) Irreversible Change.
(vi) Irreversible Change.

Question 6.
Write some changes that you see around yourself.
Answer:

1. The flowers bloom
2. Nails grow
3. Hair grow
4. body weight increases or decreases
5. Leaves fall from tree
6. Colour of leaf changes from green to yellow etc.

Question 7.
Write few changes that cannot be reversed.
Answer:

1. Breaking of a glass.
2. Germination of seed.
3. Grain to its flour.

Question 8.
Write few changes which can be reversed.
Answer:

1. Cold milk to hot milk.
2. Melting of ice cream.
3. Stretched rubber band to its normal size.

Question 9.
Most physical changes are reversible. Give reasons with two examples.
Answer:
Most physical changes are reversible because no new products are formed. The original products can be obtained on reversing the reaction. For example,

• Water on freezing changes to ice and on heating ice, again water can be obtained.
• Wax melts on heating. On cooling, again the wax can be obtained.

Question 10.
Classify the following as reversible or irreversible changes :
(i) Growth of a plant.
(ii) Ploughing a field.
(iii) Melting of wax.
(iv) Falling of rain.
(v) Pulling of rubber string.
(vi) Breaking of a glass rod.
(vii) Cooking of food.
Answer:
Reversible changes : Ploughing a field, Melting of wax, Pulling of rubber string.

Irreversible changes : Growth of a plant, Falling of rain, Cooking of food, Breaking a glass rod.

Long Answer Type Questions

Question 1.
Explain the following terms :
(i) Reversible change
(ii) Irreversible change
(iii) Contraction
(iv) Evaporation
(v) Condensation
(vi) Combustion.
Answer:
(i) Reversible changes. The changes in which original substances can be recovered by reversing the process, are called reversible changes, e.g. when wax is heated, it melts and when the liquid wax is cooled, it solidifies.

(ii) Irreversible changes. The changes in which the original substance cannot be recovered by reversing the process are called irreversible changes, e.g. formation of ash by burning coal.

(iii) Contraction. It is the property of substance by which the size of the substances decreases on cooling.

(iv) Evaporation. The process of conversion of liquid into vapour state by heating is known as evaporation.

(v) Condensation. The process of conversion of vapours into liquid by cooling is known
as condensation.

(vi) Combustion. Some substances start burning on heating. This is called combustion. If we light a candle, the wax in the wick bums.

Question 2.
State the reason for following :
(i) Heating of metal rim to fix on wooden wheel.
(ii) Storing of cooked food in refrigerator.
(iii) Coating of iron sheet with tin before making a can.
(iv) Cutting of trees for fuel and furniture.
(v) Burning of a candle.
Answer:
(i) Metal rim is at first heated so that it increases in size. It is then slipped on wooden wheel. Water is poured on it so that iron rim contracts on cooling and fixes firmly to hold the wooden wheel.

(ii) Bacteria and microbes can easily spoil cooked food at room temperature. But in refrigerator, the temperature is low as compared to outside which prevents (inhibits) the growth of the microbes. So, cooked food is kept in refrigeration to prevent it from spoiling.

(iii) Iron sheet can easily rust in presence of air and moisture. But tin cannot rust. So, iron sheet is coated with tin to prevent from rusting.

(iv) Trees are being cut for fuel and other numerous wood items. But cutting of trees lead to many adverse effects, such as soil erosion, less rain fall, unfertile soil etc. So, cutting of trees must be banned.

(v) A candle burns involves both chemical and physical change. In it some wax melts into liquid form while some converts into gas which bum in air to give a flame.