Science [5 Marks Each] QUE-ANS

1. Yes, by condensation water vapour can be converted into water.
2. Yes, by evaporation water converted into its vapour form.
3. Yes, by freezing water converted into ice.
4. Not possible.

1. Made a dough this change cannot be reversed.
2. Rolled the dough to make a chapatti. This change can be reversed.
3. Baked the chapatti on a pan, this change cannot be reversed.
4. Dried the chapatti and ground it in a grinder to make powder, this change cannot be reversed.

To explain the differences between changes that can or cannot be reversed, some examples are given below:

1. If we inflate a balloon, the size and shape of the balloon undergoes a change. However, the original size and shape of the balloon can be obtained back by allowing the air to escape from the balloon. This means that the change that occurs by inflating a balloon can be reversed. But, if the balloon bursts after being inflated, then its original size and shape cannot be obtained back. Thus, in this case, the change cannot be reversed.
2. If we fold a piece of paper, then the shape and size of the paper undergoes a change. In this case, the original shape and size of the original paper can be obtained back. Thus, this change can be reversed. However, if we cut the piece of paper, the change in the shape and size of the paper cannot be reversed.
3. After we roll out a chapatti from a ball of dough, the chapatti can be converted back into a ball. Thus, the change occurring here can be reversed. But, if we cook the chapatti on a tawa, then it cannot be converted back into a ball of dough. Thus, the change is irreversible.

Fixing of a metal rim on an wooden wheel and fixing of wooden handles in iron blade in agricultural tools are such examples.
The iron blade of these tools has a ring in which the wooden handle is fixed. Normally, the ring is slightly smaller in size than the wooden handle. To fix the handle, the ring is heated and it becomes slightly larger in size (expands). Now, the handle easily fits into the ring. When the ring cools down, it contracts and fits tightly onto the handle.
Such a change is also used for fixing the metal rim on a wooden wheel of a«cart as shown in Fig. Again the metal rim is made slightly smaller than the wooden wheel. On heating, the rim expands and fits onto the wheel. Cold water is then poured over the rim, which contracts and fits tightly onto the wheel.

The example of each case is as follows:

1. Heating of an iron rod.
2. Baking of chapatti.
3. Formation of ice from water.
4. Formation of salt solution.
5. Mixing of cement and water.

Reversed changes are as follows:

1. Simba blew balloons and put them on the wall.

4. Making of some flowers by origami (paper folding) to decorate the house.
5. Her father made dough balls.
6. Mother rolled the dough balls to make puries
7. Mother heated oil in a pan.

Changes that cannot be reversed are as follows:

2. Some of the balloons got burst.

3. Paheli cut colourful strips of paper and put them on the wall with the help of tape.

8. Father fried the puries in hot oil.