Important Questions for Class 6 Science Chapter 6 Changes Around us
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Multiple Choice Questions
Which of the following is a desirable and undesirable changes?
(a) Burning of House
(d) Burning of cooking gas
(e) rusting of iron
(f) souring of milk
(g) rottening of fruits
(e) breaking of glass tumbler
The process of converting solid directly into gas
Which of the following is a slow and fast changes?
(a) burning of paper
(b) formation of coal
(c) growth of the baby
(d) Rusting of iron
(e) Burning a matchstick
(f) Switching on the bulb
Which of the following is an example of non periodic change?
(c) truck accident
(d) Rotation of fan
(e) Movement of earth around sun
(f) Phases of moon
The process of converting gas directly into solid?
Which one of these is not true?
(a)Change in which heat is given out is called exothermic changes.
(b) Changes that cannot be reversed is called irreversible changes
(c) Iron contracts on heating and expand on cooling
(d) None of these
Which of the following is a reversible change?
(a) burning of forests
(b) Ripening of fruits
(c) burning of candle
(d) Melting of ice
Match the column
(P) Changes in which heat is liberated
(Q) change in which new substance is formed
(Y) Endothermic Changes
(R) changes take place by absorption of heat
(Z) exothermic changes
Which of these are correct?
(a) P -> X, Q -> Y, R -> Z
(b) P -> Y, Q -> X, R -> Z
(c) P -> Z, Q -> Y, R -> X
(d) P -> Z, Q -> X, R -> Y
Iron rim is made slightly smaller than the wooden wheel. The rim is usually heated before fixing into the wooden wheel, because on heating the iron rim
(a) expands and fits onto the wooden wheel.
(b) contracts and fits onto the wooden wheel.
(c) no change in the size takes place.
(d) expands first, then on cooling contracts and fits onto the wooden wheel.
Salt can be separated from its solution (salt dissolved in water), because
(a) mixing of salt in water is a change that can be reversed by heating and melting of salt.
(b) mixing of salt in water is a change that cannot be reversed.
(c) mixing of salt in water is a permanent change.
(d) mixing of salt in water is a change that can be reversed by evaporation.
1. Desirable changes (d)
Undesirable changes All rest of them
3. Slow changes (b),(c),(d)
Fast changes (a),(e),(f)
4. (a) (b) (c)
SHORT ANSWER TYPE QUESTION
How to achieve tight fit of the handle in tools like iron axle? Question 12
With the help of examples explain what is periodic and what is non periodic changes. Question 13 Name few changes that Rajesh observed while burning a candle. Question 14
A bag of cement & a bag of sand was mixed together with water. Was the change that occurred reversible or irreversible? Can we use any method of separation that you learned in previous chapter to separate those ingredients? Question 15
Why do we classify the changes taking place around us? Check your Answers(11-15)
11.In order to make tools like an axe, the ring of its iron blade is heated which allows it to expand, then the wooden handle is inserted inside the ring and the iron is allowed to cool which makes it contract and tightly grip the wooden handle.
12. example of periodic change is occurring of day & night, changing of season, these changes occur or repeat itself after a fixed interval of time. While example of non-periodic changes would be occurrence of cyclone, eruption of volcano, tsunami, these changes doesn’t have a fixed interval of time after which it repeats itself.
13.He observed melting of wax, which is a reversible physical change,
He also observed solidification of the melted wax as it cooled down
Next, he saw the burning of flame which is irreversible chemical change.
14.It's an irreversible change.
No, we cannot get back the original ingredients as chemical change takes place and the new item formed has no similarity with original ingredients.
15.We classify the changes taking place around us so that we can have better understanding of these changes.
Is recycling of paper/plastics or any other product is a reversible change? Question 17
‘Though trees are planted after deforestation then can it be considered as a reversible change?’ Justify the statement Question 18
list two irreversible physical changes. Question 19
Do you think we break molecules when we turn chalk into chalk powder? Question 20
Rashi while performing a chemistry experiment had put the hot test tube under cold water which immediately cracked. Why do you think the test tube cracked? Check your Answers(16-20)
16.No, recycling of any product is not a reversible change. Though after recycling paper we get back paper and after recycling plastic we get plastic but it is never like the original product.
17.No, deforestation can’t be considered as a reversible change because no same tree can be planted after felling or cutting.
18.Grinding of wood into sawdust
Breaking of a glass beaker into pieces
19.No, because no new substance is formed, molecules of chalk and chalk powder are same.
20.this is due to contraction when outer surface of glass comes in direct contact with the cold water then it contracts more compared to the inner surface of the glass i.e. not direct contact with the cold water.