SCIENCE Ch 6. Changes around Us WORKBOOK ANSWER

 Ch 6. Changes around Us 

Objective type questions

1. Multiple choice questions 

(a) Which of the following is not an example of an irreversible physical change? i. crushing of wood into sawdust ii. cutting of grass 

iii. heating an iron rod iv. grinding of wheat into flour Ans: heating an iron rod 

(b) In which of the following examples, a physical and a chemical change is  occurring simultaneously? 

i. rusting of iron ii. burning of candle 

iii. dissolving salt in water iv. adding baking soda to vinegar Ans: burning of candle 

2. State whether true or false. Correct the false statements. 

(a) Application of heat can bring about both physical and chemical changes.  Ans: True  

(b) Reversible physical changes are the changes in which the original form of the  substance cannot be restored. 

Ans: False 

Reversible physical changes are the changes in which the original form of  the substance can be restored. 

3. Give two examples of : 

(a) Physical changes 

Ans: breaking of glass, tearing of paper, freezing of water, melting of ice 

(b) Man-made changes 

Ans: Cutting of wood, making of paper, growing food in fields, burning fuels  and making dams 

(c) Slow changes 

ans: Growth of plants and animals, Formation of rocks, soil and fossil fuels,  Formation of mountains, Soil erosion 

4. In the following questions, two statements are given- one labelled  Assertion (A) and the other labelled Reason (R). Read the statements  carefully and choose the correct alternative (A), (B), (C) and (D) as given  below. 

(A) Both A and R are true and R is correct explanation of the assertion. (B) Both A and R are true but R is not the correct explanation of the assertion. (C) A is true but R is false. 

(D) A is false but R is true. 

(a) Assertion: Rotting of food is an example of an undesirable change. Reason: Changes that are useful to us are known as undesirable changes. (C) A is true but R is false. 

(b) Assertion: Adding baking soda to vinegar results in a chemical change with the  evolution of carbon dioxide gas. 

Reason: When two or more substances are mixed they may react with each  other to form a new substance. 

(A) Both A and R are true and R is correct explanation of the assertion. 

Theory type questions

5. Answer in brief: 

(a) What is a change? Explain why water cycle is considered as an example of  reversible change. 

Ans: ∙ The transformation either in the appearance, properties or functions of  a substance is called a change. 

∙ The water cycle is based on the interconversion of the three physical  states of water. 

∙ Processes such as melting, boiling, evaporation, freezing, condensation  that are part of the water cycle are reversible changes. 

∙ In these changes, there is a change in the state of matter but a new  substance is not formed. 

(b) ‘ The property of solids to expand and contract is used in making the wooden  wheel of a cart. Explain. 

Ans: ∙ The diameter of the metal rim is kept slightly smaller than the  diameter of the wooden wheel.  

∙ When the metal rim is heated, it expands and can easily be placed on  

the wooden wheel.  

∙ Cold water is then poured to cool the metal rim. Once cooled it  contracts and fits tightly onto the wheel. This helps in the smooth  movement of the wheel and less wear and tear of the wood.  

∙ In making of a spade, the iron blade is heated so that it expands and  fits onto the wooden handle. After cooling the iron blade contracts and  remains firmly attached to the handle. 

(c) Differentiate between: 

i. Physical change and Chemical change 

Ans: 

Physical change	chemical change
There is no change in the identity  of the substance (matter)   undergoing the change.	The identity of the substance   undergoing the change is lost.
No new products are formed, only  the form (state) of the substance  changes.	New products with completely  different properties from the one  started with are formed.
Most physical changes can be  reversed by simple methods.	Most chemical changes cannot be reversed by simple methods.

ii. \Natural and Artificial changes  

Ans: 

natural changes	artificial changes
The changes around us that take  place without any human efforts;  are called natural changes.	The changes which occur only with  human effort are called man-made  changes or artificial changes.
ex: Change of seasons, transition  from day to night, blowing of  winds, earthquakes	ex: cutting of wood, making of paper,  growing food in fields, burning fuels  and making dams

6. Give reasons for the following: 

(a) Gaps are left between railway tracks. 

Ans: Heat causes metals to expand. Gaps are left between railway tracks to  allow the expansion of the metal during summer. Otherwise, the tracks  would bend and may cause accidents. Hence gaps are left between the  railway tracks. 

(b) Melting of ice is a reversible process. 

Ans: Ice kept out of the refrigerator, begins to melt and changes into water. If  the same water is put back into the freezer, it changes back to ice. Hence,  melting of ice is a reversible process.

Picture based questions

7.

(a) What causes the change in the object as seen in the picture? 

Ans: Pressure 

(b) Describe the changes in the object at the molecular level. 

Ans: ∙ When we apply pressure, the molecules of a substance undergo a  change in terms of their position.  

∙ In most cases, the substance regains its original state or shape as soon  as the pressure is released. 

  

Activity based question 

  

8. Picture A Picture B Picture C 

Why does the metal ball slip through the ring in picture A but not in picture C? Ans: On heating, the ball expands and increases in diameter. This restricts the  ball from slipping through the ring in picture C. After cooling, the metal  ball contracts and slips through the ring in picture A. 

Fun based questions

9. Classify the changes given below into fast and slow changes. 

Burning of paper	Fast
Change in weather	Slow
Spinning of top	fast
Occurrence of day and night	slow

HOTS 

10. 

(a) How will you separate two steel vessels that are stuck to each other? Ans: The two steel vessels can be separated from each other by heating since  heating results in the expansion of metal vessel. 

(b) Sonam mixes all the materials required to make a chocolate cake and then she  bakes the mixture in the oven. List different types of changes taking place while  making the cake. 

Ans: chemical ,irreversible, slow and desirable 

 

SCIENCE CHAPTER 6 CHANGES AROUND US TEXTBOOK ANSWER

 

SCIENCE CHAPTER 6 CHANGES AROUND US

Q.4 classify following in physical and chemical changes 

 

Physical changes	Chemical changes
Melting of an ice-cream Melting of wax Lighting of a bulb Formation of fog Formation of cloud	Baking of cake Burning a paper Boiling of egg Lighting of matchsticks Formation of coal Curdling of milk

Q.5 Answer the following questions in short.

a.) list three main causes of change

Ans. 1) Pressure 

         2) Heat

         3) Mixing

b) Give two examples of each of the following

  i) Man-made changes – 1)Cooking

                                              2)Making  dams

ii) Reversible changes – 1) Melting ice

                                           2) Water cycle

iii) Undesirable changes – 1) Earthquake

                                               2) Rotting of food  

c) State one difference between desirable changes and undesirable changes.

Q.6 Define the  following

a) Irreversible changes :- A change that can not be reversed 

Example :- cooking of food

b) Fast change :-changes those occur in short time are called fast changes.

Example :- floods ,burning of fossil fuels

c) Chemical changes :- A change in which both physical and chemical properties are altered and a new substance is formed ia called chemical changes. Example :- Rusting of iron

Q.7 Give reasons 

1. Digestion is a chemical change as well as a physical change 

      In digestion process food is physically  broken down by chewing and chemically broken down by digestive enzymes in the saliva and the acid in the stomach

2. Metals are used for making tools

     Because metal melts on heating and contracts on cooling. That’s why its easy to mould metal in any shape 

Q.8 

a)How is the melting of wax is different from burning of wax?

       Melting of wax is physical change because only physical state is changing from solid to liquid but burning of wax is chemical change because in burning, wax reacts with oxygen present in surroundings and forms carbon dioxide and ash.

b) How does mixing bring about a change? Explain with the help of a example.

When substances are mixed together, it can result either in a physical change or a chemical change. Example: If iron and sulphur are mixed, no chemical change occurs. But when the mixture is heated, it glows after some time and a black substance is formed which is different from iron and sulphur.

c) Why are gaps left between railway tracks?

    Metal expands and contracts due to temperature changes. That’s why  There is gaps between rail sections to allow for expansion and contraction of the metal in summer and winter due to temperature changes. 

Q.11 HOTS( Higher Order Thinking Skills)

Why is the burning of LPG gas considered to be both physical and a chemical change ? 

      A change in which both physical and chemical changes occur is burning of LPG gas. Liquefied petroleum gas is filled in the cylinder in the form of a liquid. When these liquids come out of the cylinder in the form of vapors, physical change takes place. When these vapors are mixed with air and burn, chemical change takes place.

The Deccan and the South Indian Kingdoms

 

The Deccan and the South Indian Kingdoms

Textual Exercise

Choose the appropriate option.

a) _____________were also known as the Andhras.

i) Chalukyas

ii) Cholas

iii) Satvahanas

iv) Cheras

b) The Chalukyan king plundered the Pallava capital, Kanchi.

 i) Pulakesin II

ii) Pulakesin I

iii) Kirtivarman II

iv) Vikramaditya

c) The inscription of Kharavela of Kalinga also given information about the South Indian kingdoms.

i) Tanjavur

ii) Hathigumpha

iii) Aihole

iv) Junagadh

d) The last ruler _________was Aparajitavarman.

i) Pallava

 ii) Pandya

iii) Chera

iv) Chola

e) The _______________of the Sangam period were popular.

i) handicrafts

ii) paintings

iii) sculptures

iv) monuments

2. Fill in the blanks.

a) The first Sangam was held at Madurai.

b) Tolkappiyam written by Tolkappiyar is the earliest Tamil literature.

c) Avvaiyar was the title given to the most legendary poetess of the Tamil literature.

3. Match the columns. Column A Column B a) Karikala i) Modern Kerala b) Cheras ii) Sittalai Sattanar c) Simhavishnu iii) Kallanai dam d) Manimekalai iv) Pallava dynasty 86

4. Answer the following questions in 10 to 20 words.

a) Name the foreign authors who wrote about the commercial contacts between the West and the South India.

Ans. Greek authors such as Megasthenes, Ptolemy, Pliny and Strabo wrote about the commercial contacts between the West and the South India.

b) Write the name of the source that gives information on the Chera rulers.

Ans. The Pugalur inscription of the fi rst century CE gives information about the three generations of Chera rulers. Padirruppattu is yet another important source that furnishes information on Chera kings.

c) Why did the Pandyan rule begin to decline?

Ans. The Pandyan rule started to decline due to the invasion of the Kalabhras.

5. Answer the following questions in 50 to 70 words.

a) Write a brief note on Gautamiputra Satakarni.

·       Gautamiputra Satakarni was the greatest ruler of the Satavahana dynasty.

·       His reign lasted for a period of 24 years from 106 CE to 130 CE.

·       He annexed the whole of Deccan and expanded his kingdom.

·       Although he was a champion of Brahmanism; he gave donations to the Buddhists.

·       The Nashik and the Nanaghad inscriptions provide valuable information about the rule of Gautamiputra Satakarni.

b) Write about on the rise of the Bhakti sect in South India.

·       From 7th century onwards, the Bhakti sect spread throughout India, particularly in the South.

·       Bhakti meant total surrender of the devotees to God.

·       In South India, the Nayanars and Alvars were the noted saints of the Bhakti sect.

·       The Nayanars, the devotees of Lord Shiva, wrote poetry in praise of Lord Shiva; the Alvars were the worshippers of Lord Vishnu.

·       During this period, devotional poetry developed.

c) Discuss about the trade during the Sangam period.

·       The well organised internal and external trade flourished during the Sangam period and that resulted in a great demand for these products.

·       Merchants used carts and animals to carry goods from place to place.

·       The barter system was an important feature of internal trade.

·       External trade was carried between South India and the Roman Empire. The port cities of Puhar, Tondi, Musiri, Korkai, Arikkamedu and Marakkanam became centres of foreign trade.

·       Roman coins were found in all parts of Tamil Nadu, which reveal the extent of the trade.