Changes Around Us

Q25. Write reversible or irreversible for each of the following change:

Ans.

Q26. Classify the change as slow or fast change.

Q27. What is evaporation? What kind of change it is? Give a reason in support of your answer.

Ans. Evaporation is the process in which water changes to gaseous state due to an increase in temperature.

Yes, it is a reversible change because water vapor can be converted back into water on cooling.

Q28. How curd is formed? Is it a reversible change?

Ans. A small quantity of curd is added to warm milk. The milk is stirred and is set aside for a few hours at a warm place. In a few hours, the milk changes into curd. This change is irreversible.

Q29. Iron blade of tools has a ring in which the wooden handle is fixed. Why the ring is made slightly smaller in size than wooden handle?

Ans. Iron blade of tools has a ring in which the wooden handle is fixed. The ring is made slightly smaller in size than wooden handle because handle fits easily as it expands on heating and contracts on cooling.

Q30. Why a thick layer of Plaster of Paris is applied over the bandage to keep the fractured bone immobilized?

Ans. When water is added to Plaster of Paris, it sets into a hard mass thus it keeps the fractured bone on its place and prevents it from moving while it heals. That’s why a thick layer of Plaster of Paris is applied over the bandage to keep the fractured bone immobilized.

Q31. Differentiate between toy aeroplane made by folding paper and toy aeroplane cutout. 

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Q32. Differentiate between making chocolates of different shapes and baking cakes of different shapes.

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