Exercises:
Q1: 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 _________________.
Ans:
(a) evaporation
(b) condensation
(c) drought
(d) flood
Q2: 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.
Ans:
(a) condensation
(b) evaporation
(c) condensation
(d) evaporation
(e) evaporation
Q3: 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.( )
Ans:
(a) False
(b) False
(c) True
(d) False
(e) True
Q4: Suppose you want to dry your school uniform quickly. Would spreading it near an anghiti or heater help? If yes, how?
Ans: Yes, spreading it near an anghiti or heater it would obsorb more heat from its surrounding, because heat causes faster evaporation.
Q5: 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?
Ans: When cooled bottle is kept out side, the air touches its cold surface. the air around it also becomes cooled, by which the process of condensation takes place causes a puddle of water around it.
Q6: To clean their spectacles, people often breathe out on glasses to make them wet. Explain why the glasses become wet.
Ans: The moist air coming out from mouthcondenses on glasses to make glass wet.
Q7: How are clouds formed?
Ans: The process of condensation plays an important role in the formation of cloud. The upper atmosphere is colder than the earth surface and it around. When water vapour goes higher from the surface of the earth, coming contact of cooled air at sufficient hight it also gets cooler. 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
Q8: When does a drought occur?
Ans: If it does not rain in a region for a year or more, The soil continues to lose water to lose water by evaporation and transpiration. Since it is not being brought back by rain, the soil becomes dry. The level or water in ponds and wells of region goes down and some of them may even dry up. The ground water may also become scarce. This situation may lead to drought.
