NCERT Solutions Class 6 Science Chapter 6 Changes Around us

NCERT Solutions for Class 6 Science for chapter 6 Changes Around us

Question.1 

To walk through a water logged area, you usually shorten the length of your dress by folding it. Can this change be reversed?

Answer.

Yes, the length of dress can again be increased by unfolding it. Therefore, it is a reversible change.

Question.2

You accidentally dropped your favourite toy and broke it. This is change you did not want. Can this change be reversed?

Answer.

No, this change cannot be reversed.

Question.3

Some changes are listed in the following table. For each change, write in the blank column, whether the change can be reversed or not. 

Answer. 

Question.4

A drawing sheet changes when you draw a picture on it. Can you reverse this change?

Answer.

If we draw a picture on a drawing sheet with a pencil, then the picture can be erased with an eraser. Therefore, we can get back the original drawing sheet. If we draw a picture on a drawing sheet with a pen, then the original drawing sheet cannot be obtained as we cannot erase ink.

Question.5

Give examples to explain the differences between changes that can or cannot be reversed.

Answer.

1. Formation of curd from milk is an irreversible change as a new product (curd) is formed. Neither any bacteria nor any change in conditions can convert curd back into milk.

2. Take a piece of paper and fold it to make a toy aeroplan We can get back the original piece of paper by unfolding it. Take the same piece of paper and draw an aeroplane on it, cut along its outline. In this condition we cannot get back the original piece of paper as pieces of paper cannot be rejoined.

3. Take some dough and make a ball. Try to roll out a chapati. After we roll out a chapati from a ball of dough, the chapati can be converted back to ball. Once we cook the chapati, it 
cannot be converted back to ball.

Question.6

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 immobilised. Can the change in POP be reversed?

Answer.

No, the change in POP cannot be reversed. Plaster of Paris (POP) has a property of setting into a hard mass on wetting with water due to the formation of a new compound called gypsum. Once the POP is hardened, it cannot be converted back into POP. Hence, it is an irreversible change.

Question.7

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?

Answer.

Cement sets into a hard mass on mixing with water. The hard mass obtained cannot be converted back to cement. Therefore, It is essential to keep cement away from rain otherwise it will change into a hard mass which is of no use.