Question 1 Define the term evaporation?
Question 2 How are clouds formed?
Question 3 Why do water drops appear on the outer surface of a glass containing ice-cold water?
Question 4 What is transpiration?
Question 5 We hang our wet clothes out to dry on a rope.What happens to the water in the clothes?
Question 6 Give few examples of evaporation in daily routine?
Question 7 What is condensation?
Question 8 Explain why, if we take out a bottle of water from a refrigerator and keep it on a table, we notice a puddle of water around it after sometime.
Question 9 How is dew and fog form?
Question 10 In order to clean spectacles, people often breathe out on glasses to make them wet.Explain, why, the spectacle glasses become wet?
Question 11 Explain why in cold winter morning, the cars that are parked in the open are wet although it has not rained in the night?
Question 12 Suppose you want to dry your school uniform quickly? Would spreading it near a heater or an angithi help? Give reason for your answer?
Also Read NCERT Solutions for Chapter 14 Water
Evaporation
When we spread wet clothes on a rope or wire , they dry up after some time. The water present in wet clothes seems to disappear. Water present in wet clothes evaporates by receiving heat from the sun (or surrounding air) to form water vapour. This water vapour goes into air. Gradually, all the water present in wet clothes evaporates and the clothes become dry. The changing of water into water vapour is called evaporation.
(1) The water spilled on the floor dries up and disappears due to evaporation.
(2) Water from wet roads and puddles near our homes and rooftops (formed during rains) also dries up and disappears by forming water vapour by the process of evaporation when the rain stops.
(3) The wet blackboard dries up after wiping it due to evaporation of water from its surface.
(4) The steam arising from wet clothes, while they are being ironed, is also a process of evaporation of water.
(5) If we want to dry our washed and wet school uniform quickly, we should spread it near a heater. The heat produced by heater will evaporate the water present in wet clothes faster rate due to which the uniform will get dry quickly.
(6) The common salt dissolved in water can be separated by the process of evaporation. When water having salt dissolved in it is heated on a burner, water evaporates (turns into vapour) rapidly and goes into the air, but the salt is left behind. This is because though water forms vapour easily on heating, salt does not form vapour (or gas) at all.
(7) When ocean water (or sea water) gets heated by the heat of the sun, then some of the ocean water evaporates to form water vapour which go into air. The salts present in the ocean water (or sea water) remain behind.
Transpiration
Plants take water from the soil to grow.Plants use a part of this water to make their food and retain some of it in their different parts. The remaining water is released by the plants into air as water vapour through the small pores in their leaves (called stomata).
The loss of water from plants as water vapour through the pores of their leaves is called transpiration. The process of transpiration puts a large amount of water vapour into the air.
Water vapour gets added to the air (or atmosphere) by the processes of evaporation and transpiration. Evaporation of water takes place from oceans, rivers ,lakes, ponds and soil whereas transpiration occurs from the leaves of plants and trees. Thus, water vapour is always present in the air.
Condensation
The mass of tiny droplets formed by the condensation of water vapour which we see floating high in the atmosphere is called a cloud. The formation of clouds involves the process of condensation. The changing of water vapour into liquid water on cooling, is called condensation.
Activity
Take a glass half filled with water and add some ice to it . Wipe the glass from outside with a piece of clean, dry cloth so as to make its outer surface completely dry. Allow this glass containing ice-cold water to stand undisturbed for about five minutes. We will see that a large number of tiny drops of water appear on the outer surface of the glass. The appearance of tiny water drops on the outer side of glass can be explained as follows : The air around the glass contains water vapour in it. When the water vapour present in air
come in contact with the cold, outside surface of glass, they get cooled and condense to form tiny drops of liquid water. Thus, water drops appear on the outer surface of a glass containing ice-cold water due to condensation (of water vapour present in air).
Condensation in daily life
(1) If we take out a bottle of ice-cold water from the refrigerator and keep it on a table, then a puddle of water is formed around it after some time. This is because when the water vapour present in air around the bottle comes in contact with the cold outer surface of bottle, it gets cooled and condenses to form liquid water which then forms a puddle of water around the bottle.
(2) We can see tiny drops of dew on the leaves of grass on the cold winter mornings. The formation of dew is also due to the condensation of water vapour present in air.
(3)During cold winter mornings, many times we see a thick white cloud like thing near the ground which reduces our visibility .This is called fog. Fog consists of a cloud of tiny water droplets suspended in the air near the ground. Fog is formed by the condensation of water vapour present in air near the ground during very cold winter morning.
(4) People often breathe out on spectacle glasses to make them wet before wiping with a piece of cloth. The spectacle glasses become wet because the water vapour present in our breath condenses on the glasses to form tiny droplets of water.
Formation of Clouds
(1) The process of condensation is involved in the formation of clouds in the sky and bringing back water to the surface of earth (in the form of rain, etc.)
(2) Water vapour formed by the process of evaporation (from oceans, rivers, lakes, ponds and soil), as well as by transpiration (from plants and trees), goes into air.
(3) The air containing water vapour is heated by the sun. Hot air, being lighter, rises high up in the atmosphere or sky.
(4) Now as we go higher and higher from the surface of earth, the temperature decreases, it becomes cooler and cooler. So, when the air containing water vapour rises to a high altitude in the atmosphere, the water vapour present in it gets cooled so much that it condenses to form tiny droplets of water.
(5) It is these tiny droplets of water, formed by the condensation of water vapour, which remain floating in air in the sky and appear to us as clouds. The tiny droplets of water in the clouds join together to form bigger drops of water.
(6) These drops of water fall down on the earth in the form of rain. During winter in very cold regions, the water drops in the sky freeze to form snow (ice). So, water also falls down to earth in the frozen state called snow. This is called snowfall, Snowfall occurs during winter in the extremely cold hilly areas of the earth. When snow lying on high mountains melts, it forms water. Sometimes the frozen water from the clouds also falls on the earth in the form of small, round pieces of ice called hail.
The snow which falls on high mountains melts slowly to form water. This water then flows down the mountains in the form of streams and rivers . Some of the rain water which falls on land also goes into rivers. Most of the rivers cover long distances on land and ultimately fall into a sea or an ocean. This is how most of the water which falls on the earth as rain goes back to the oceans.
The rain water also flows into lakes and ponds to fill them. It is also held by the soil. Some of the rain water which falls on earth seeps through the soil and goes under the surface of earth. Ultimately this water is stopped by some hard rocks and collects there. This water becomes available to us as ground water or rather underground water. It is this ground water which we take out for our use by digging wells and tube-wells or by installing and pumps.
| Notes for Chapter 14 Water |
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