NCERT Solutions Class 7, Social Science, Geography, Chapter- 5, Water.
Exercises
1. Answer the following questions.
(i) What is precipitation?
Solution:
Sun’s heat causes water to evaporate. When the water vapour rises, it begins cooling. The condensing water vapour forms droplets of water. Masses of such water droplets form clouds and float in air. When these droplets become too heavy to float in air, they fall upon land or sea in the form of rain, snow, or sleet. This is known as precipitation.
(ii) What is water cycle?
Solution:
The water present on the Earth’s surface (on land and in water bodies) gets evaporated by the Sun’s heat. The water vapours rise, condense and form clouds. When the clouds become heavy, the condensed water vapours fall back upon land or sea in the form of rain, snow or sleet. The processes of evaporation, condensation and precipitation continue in a cyclical manner. This way, water continually changes its form and circulates between oceans, atmosphere and land. This continuous circulation of water is known as the water cycle.
(iii) What are the factors affecting the height of the waves?
Solution:
Waves are formed when winds scrape across the ocean surface. Winds blowing at very high speed form huge waves. An earthquake, a volcanic eruption, and underwater landslides also affect the height of waves. Such phenomena can shift large amounts of ocean water, thereby causing huge waves to be formed.
(iv) Which factors affect the movement of ocean water?
Solution:
The movements that occur in oceans are broadly categorised as waves, tides, and currents.
The factors affecting these movements of ocean water are as follows:
(a) Waves are formed as a result of winds, earthquakes, volcanic eruptions, and underwater landslides.
(b) Tides are caused by the strong gravitational pull exerted by the Sun and the Moon on the Earth’s surface.
(c) Another factor affecting the movement of ocean water is temperature. Ocean currents are formed because of the temperature differences between the ocean water present at different latitudes.
(v) What are tides and how are they caused?
Solution:
Tides are the rhythmic rise and fall of ocean water that occurs twice in a day. The strong gravitational pull exerted by the sun and the moon on the earth’s surface cause the tides.
(vi) What are ocean currents?
Solution:
Ocean currents are streams of water flowing constantly on the ocean surface in definite directions.
2. Give reasons.
(i) Ocean water is salty.
Solution:
The ocean bodies and the seas contain salty water. The water of oceans is salty or saline as it contains a large amount of dissolved salts. Most of this salt is sodium chloride.
(ii) The quality of water is deterioting.
Solution:
Though three-fourth of the Earth’s surface is covered with water, almost 98% of it is unfit for use. Oceans and seas, which constitute the major portion of the hydrosphere, contain saline water. The freshwater reserves of the Earth are mostly made up of ice-caps, groundwater, lakes, and rivers. The quantity of water on Earth remains the same. It constantly changes form and circulates between oceans, atmosphere, and land. Considering that the freshwater reserves remain constant and that the world population rises day-by-day, it is important that we use these water resources judiciously. However, due to factors like deforestation, industrial and agricultural pollution of rivers and lakes, wastage of water, pollution of groundwater, etc., the quality of water that is available to many people in this world today is not suitable for human consumption.
3. Tick the correct answer.
(i) The process by which water continually changes its form and circulates between oceans, atmosphere and land
(a) Water cycle (b) Tides (c) Ocean currents
The correct ption is : (a) Water cycle
(ii) Generally the warm ocean currents originate near
(a) Poles (b) Equator (c) None of these
The correct ption is : (b) Equator
(iii) The rythmic rise and fall of ocean water twice in a day is called
(a) Tide (b) Ocean current (c) Wave
The correct ption is : (a) Tide
4. Match the following.
(i) Caspian Sea
(ii) Tide
(iii) Tsunami
(iv) Ocean currents
|
(a) Largest lake
(b) Periodic rise and fall of water
(c) Strong seismic waves
(d) Streams of water moving along definite paths
(e) Water cycle |
Solution:
| (i) Caspian Sea |
(a) Largest lake |
| (ii) Tide |
(b) Periodic rise and fall of water |
| (iii) Tsunami |
(c) Strong seismic waves |
| (iv) Ocean currents |
(d) Streams of water moving along definite paths |
