Chapter 14: Water (Solutions)
Posted on : 13-06-2018 Posted by : Admin

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1. Fill up the blanks in the following:

(a) The process of changing of water into its vapour is called evaporation.

(b) The process of changing water vapour into water is called condensation.

(c) No rainfall for a year or more may lead to drought in that region.

(d) Excessive rains may cause floods.     

2. State for each of the following whether it is due to evaporation or condensation:

(a) Water drops appear on the outer surface of a glass containing cold water. Condensation

(b) Steam rising from wet clothes while they are ironed. Evaporation

(c) Fog appearing on a cold winter morning. Condensation

(d) Blackboard dries up after wiping it. Evaporation

(e) Steam rising from a hot girdle when water is sprinkled on it. Evaporation

3. Which of the following statements are “true”?

(a) Water vapour is present in air only during the monsoon. (False)

(b) Water evaporates into air from oceans, rivers and lakes but not from the soil. (False)

(c) The process of water changing into its vapour is called evaporation. (True)

(d) The evaporation of water takes place only in sunlight. (False)

(e) Water vapour condenses to form tiny droplets of water in the upper layers of air where it is cooler. (True)

4. Suppose you want to dry your school uniform quickly. Would spreading it near an anghiti or heater help? If yes, how

Answer: Yes, spreading it near anghiti or heater will help in drying the school uniform quickly as the heat will vaporize the water of the wet clothes.

5. Take out a cooled bottle of water from refrigerator and keep it on a table. After some time you notice a puddle of water around it. Why??

Answer: When we take out a cooled bottle of water from refrigerator and keep it on a table, we can notice a puddle of water around it after sometime. It is due to the phenomenon of condensation. This is because the air around the bottle gets condensed after hitting the cooled bottle.

6. To clean their spectacles, people often breathe out on glasses to make them wet. Explain why the glasses become wet.

Answer: The exhaled air contains water vapour. Thus water vapor released during the exhalation hits the glasses of the spectacles and then gets condensed in the presence of air surrounding it. Consequently the glasses are made moist thus easy to clean.

7. How are clouds formed?

Answer: Clouds are formed due to the process of CONDENSATION. Condensation plays an important role in bringing water back to the surface of earth. As we go higher from the surface of the earth, it gets cooler. When the air moves up, it gets cooler and cooler. At sufficient heights, the air becomes so cool that the water vapour present in it condenses to form tiny drops of water called droplets. It is these tiny droplets that remain floating in air and appear to us as clouds.

8. When does a drought occur?

Answer: If it does not rain in a region for a year or more, the soil continues to lose water by evaporation and transpiration. Since it is not being brought back by rain, the soil becomes dry. The level of water in ponds and wells of the region goes down and some of them may even dry up. The ground water may also become scarce. This may lead to drought.

In drought conditions, it is difficult to get food and fodder. People and animals would not have enough food and water. Even there would not be any water to grow crops.

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