Sunday, 5 June 2011

Water : Class VI Science Lesson 14:

NCERT Class VI Science textbook:
Lesson 14: Water.

Exercise


1.Question. Fill up the blanks.
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.

2.Question. State for each of the following weather 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 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.Question.Which of the following state mentioned are "True"?
Answer.(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 from tiny droplets of water in the upper layer of air where it is cooler. (True)

4.Question.Suppose you want to dry your school uniform quickly. Would spreading it near an anghiti or heather help? if   Yes, how?
Answer. spreading it near an anghiti will help, because due to more heat around, evaporation will be faster.

5.Question. 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 cool surface of cooled bottle cools the air around it, and the water vapour of the air condenses on the surface of the bottle.
 
6.Question. To clean their spectacles,people often breath out on glasses to make them wet. Explain while the glasses become wet ?
Answer. The most air coming out from mouth condenses on glasses to make glasses wet.

7.Question.How are clouds formed?
Answer.The process of condensation plays  an important role information 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 hights the air becomes so cool That the vapour present in  it condenses to from drops of water called droplets. It is these tiny droplets that remain floating in air and appear to us as cloud.

8.Question. When does a drought occur?
Answer. It does not rain for on two or year, 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.

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