Class 7 Social Science Water Exam Notes. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.
Water is an invaluable natural resource, as it sustains life on the earth. The earth is probably the only heavenly body in the entire Solar System, which is known to have water. It is estimated that about 71 per cent of the earth's surface is under water, but about 3 percent of the total water, available on the earth is the freshwater.
(i) The sun's heat causes evaporation of water vapour. When the water vapour cools down. It condenses and forms clouds. From there it may fall on the land or sea in the form of rain, snow or sleet.
(ii) The process by which water continually changes its form and circulates between oceans atmosphere and land is known as the water cycle.
(iii) Our earth is like a terrarium. The same water that existed centuries ago still exists today. The water used to irrigate a field in Haryana may have flowed down the Amazon River a hundred years ago.
(iv) The major sources of fresh water are the rivers, ponds, springs and glaciers. The ocean bodies and the seas contain salty water. The water of the oceans is salty or saline as it contains large amount of dissolved salts. Most of the salt is sodium chloride or the common table salt that is used in eating.
(1) Distribution of water bodies.
1.Oceans 97.20 Saline water
2.Ice caps and glaciers 2.00
4.Freshwater lakes 0.01
5.Inland seas 0.01
6.Atmosphere 0.002 Freshwater
9.Soil moisture 0.095
(2) The water is found on the earth's surface in oceans, seas, bays, gulfs, lakes, ponds, rivers, etc.
The water portion of the earth's surface is known as hydrosphere. The total volume of water in the hydrosphere, which is fixed and never changes, is estimated at about 1400 million cubic kilometers. One cubic kilometer has about 1000 million tons of water.
(a) The water always changes its form as liquid.,solid and gas.
(b) The process by which water changes its form and also circulates between lithosphere, atmosphere and hydrosphere is known as the water cycle or the hydrological cycle.
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