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 droughts 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.
(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.
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.
4). Suppose you want to dry your school uniform quickly. Would spreading it near an anghiti or heater help? If yes, how?
Yes. Evaporation is rapid at high temperatures. Therefore, to dry the school uniform quickly, spread the uniform near the anghiti or heater.
5). Take out a cooled bottle of water from the refrigerator and keep it on a table. After some time you notice a droplets of water around it. Why?
The cooled bottle of water has a cold surface as compared to the surrounding temperature. The water vapour present in the surrounding air condenses on the surface of the bottle. This goes on continuously and after some time we can see droplets of water around the surface.
6). To clean their spectacles, people often breathe out on glasses to make them wet. Explain why the glasses become wet.
The breath-out gas contains water vapour. The water vapour condenses on the spectacles and the glass becomes wet. It becomes easier to clean wet glass.
7). How are clouds formed?
As air rises higher from the surface of the earth, it gets cooler. As it 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 the air and appear to us as clouds.
8). When does a drought occur?
If it does not rain in a region for a year or more, 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 groundwater may also become scarce. This may lead to drought.
1). Fill in the blanks
i). On heating, water changes into its vapour.
ii). Evaporation takes place from all open surfaces of water.
iii). Evaporation of water is a slow process.
iv). Water vapour enters the air through the processes of evaporation and transpiration.
v). Snow in the mountains melts into water.
vi). In drought conditions, it is difficult to get food and fodder.
2). Write whether True or False.
i). Our water requirement is limited to households only.
ii). Water is used in industries for producing almost all the things that we use.
iii). The water in the oceans and seas has many salts dissolved in it.
iv). Water in the seas and oceans is fit for drinking.
v). Water that we use is not salty.
vi). Water vapour carries away the salts with it.
vii). The process of evaporation plays an important role in bringing water back to the surface of the earth.
Answer the following.
1). What are the sources of water?
The sources of water are seas, oceans, rivers, ponds, lakes, wells, tube wells, etc.
2). Name the uses of water?
Water is used for drinking, bathing, washing, agriculture and the industries.
3). Seawater is saline. Give reason.
The water in the oceans and seas has many salts dissolved in it. Therefore seawater is saline.
4). Seawater is not fit for drinking. Give reason.
The water in the oceans and seas has many salts dissolved in it. Therefore Seawater is not fit for drinking.
5). Write a note on the water cycle.
Water from the ocean and surface of the earth goes into the air as vapour; returns as rain, hail or snow and finally goes back to the oceans. The circulation of water in this manner is known as the water cycle.
6). Write the main effects of floods.
The effects of floods are as follows.
i). Rise in the level of water in rivers, lakes and floods.
ii). The crop fields, forests, villages and cities get submerged by water.
iii). Floods cause damage to crops, animals, property and human life.
7). Write about different methods of rainwater harvesting.
Two techniques of rainwater harvesting are as follows.
1). Rooftop rainwater harvesting: In this system, the rainwater is collected from the rooftop to a storage tank, through pipes. This water may contain soil from the roof and need filtering before it is used. Instead of collecting rainwater in the tank, the pipes can go directly into a pit in the ground. This then seeps into the soil to recharge or refill the groundwater.
2). Another option is to allow water to go into the ground directly from the roadside drains that collect rainwater.
2) Define the following
The process of conversion of water vapour to water is called condensation.
The change of water to water vapour is called as evaporation.
The loss of water in the form of water vapour through the holes present in the leaves is called transpiration.
4). Rainwater harvesting.
Collecting the rainwater and using it some other time is called as rainwater harvesting.
A part of the rainwater that seeps into the ground accumulates and is called groundwater.
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