Chapter 14 Water
Question 1: Fill up the blanks in the following:a) The process of changing of water into its vapour is called _________________.
b) The process of changing water vapour into water is called _________________.
c) No rainfall for a year or more may lead to _________________ in that region.
d) Excessive rains may cause _________________.
Answer:
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 flood.
Question 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.
b) Steam rising from wet clothes while they are ironed.
c) Fog appearing on a cold winter morning.
d) Blackboard dries up after wiping it.
e) Steam rising from a hot girdle when water is sprinkled on it.
Answer:
a) Condensation
b) Evaporation
c) Condensation
d) Evaporation
e) Evaporation
Question 3: Which of the following statements are “true”?
a) Water vapour is present in air only during the monsoon. ( )
b) Water evaporates into air from oceans, rivers and lakes but not from the soil.( )
c) The process of water changing into its vapour, is called evaporation. ( )
d) The evaporation of water takes place only in sunlight. ( )
e) Water vapour condenses to form tiny droplets of water in the upper layers of air where it is cooler. ( )
Answer:
a) False
b) False
c) True
d) False
e) True
Question 4: Suppose you want to dry your school uniform quickly. Would spreading it near an anghiti or heater help? If yes, how?
Answer: Yes, anghiti or heater will help to dry the school uniform quickly as the air surrounding anghiti or heater will get heated. In heated area evaporation takes place faster.
Question 5: Take out a cooled bottle of water from refrigerator and keep it on a table. After some time you notice a droplets of water around it. Why?
Answer: The cooled water bottle has very cold surface. Due to cool surface there is condensation of water-vapour from air on the surface of water bottle because water vapour is present in atmosphere. The condensed water molecules spread around the bottle. So a puddle of water is noticed after sometime.
Question 6: To clean their spectacles, people often breathe out on glasses to make them wet. Explain why the glasses become wet.
Answer: The air we breathe out contains water vapour which condenses on the surface of the spectacles. So, the glass becomes wet and with the help of a small amount of water molecules, it becomes easier to clean the spectacles.
Question 7: How are clouds formed?
Answer: The process of 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. It so happens that many droplets of water come together to form larger sized drops of water. Some drops of water become so heavy that they begin to fall. These falling water-drops are, what we call rain. In special conditions, it may also fall as hail or snow. Thus, water in the form of vapour goes into air by evaporation and transpiration, forms clouds, and then comes back to the ground as rain, hail or snow.
Question 8: When does a drought occur?
Answer: If it does not rain for two or more years, 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.
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