शनिवार, 22 जुलाई 2017


Question 1.Fill up the blanks in the following:
(a)The process of changing or 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: Fill up the blanks in the following:
(a)The process of changing or 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 drought.
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 form 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 water droplets of water in the upper layers of air where it is cooler.
Answer: (a) =F, (b) =F, (c) =T, (d) =F, (e) =T.
Question 4.Suppose you want to dry your school uniform quickly. Would spreading it near an anghiti or heater help? If yes how?
Answer: Spreading it near heater or anghiti will help because due to more heat around, evaporation will be faster.
Question 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: The cold surface of cooled air around it, and the water vapour of the air condenses on the surface of the bottle.
Question 6.To clean their spectacles, people often breathe out on glasses to make them wet. Explain why the glasses become wet?
Answer: The moist air coming out form mouth condenses on glasses to make glasses wet.
Question 7.How are clouds formed?
Answer: The process of condensation plays an important role in formation of cloud. As water vapour goes 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 water droplets. It is these tiny droplets that remain floating in air and appear to us as clouds.
Question 8. When does a drought occur?
Answer: If it does not rain for one or two years, the soil continuous 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 scare. This may lead to drought.

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