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Class 7 NCERT Solutions Geography Chapter 5 - Water

Water Exercise 37

Solution 1


(i) The heat emitted by the Sun causes water to vapourise. When the vapour rises in the air, it begins to cool and transforms into droplets of water. Masses of such droplets transform into clouds and float in the air. When the clouds become too heavy to float, they fall upon land or sea in the form of rain, snow or sleet. This whole phenomenon is known as ‘precipitation’.




(ii) The water on the Earth’s surface is evaporated by the heat emitted by the Sun. The vapour rises up with the air, condenses and transforms into clouds. When the clouds become too heavy to float in the air, they fall right back on land as either rain or snow or sleet. This process of evaporation, condensation and precipitation continues in a cycle which means that the water on Earth changes form continuously between oceans, atmosphere and land. This is called the ‘water cycle’.




(iii) Primarily, waves are formed due to the winds travelling across the ocean surface. High speed winds form bigger waves. Also, volcanic eruptions, earthquakes and underwater landslides affect the height of waves.




(iv) The factors that affect the movement of ocean water in terms of waves, tides and currents are as follows:


  - Waves are created because of winds, earthquakes, volcanic eruptions and underwater landslides.


  - Tides are caused by the strong gravitational pull that is exerted on Earth by the Moon and the Sun.


  - The temperature differences in ocean water situated at different latitudes results in the creation of water currents.




(v) Tides refer to the rhythmic rise and fall of ocean water levels that occur twice in a single day. A high tide is when ocean water rises to its highest levels and covers much of the shore. A low tide is when the water recedes from the shore and falls to its lowest level. Tides are the result of the huge gravitational pressure exerted on Earth’s surface by the Sun and the Moon.


(vi) Ocean currents refer to the streams of water that flow continuously on the surface of oceans.  They are formed as a result of temperature differences in ocean water situated at different latitudes.


Solution 2

(i) The oceans are constituted of water that is saline, i.e., it has a very high quantity of dissolved salt. Therefore, ocean water is salty.

(ii) Throughout human history, and especially since the onset of the Industrial Revolution,  water has been polluted in some or the other form by humans. The large scale deforestation, pollution of rivers, lakes and reservoirs due to industrial activity and agricultural production, pollution of groundwater, wastage and lack of treatment facilities in some countries have started a process of degradation of water as a resource. As a result, the quality of water on Earth is gradually deteriorating.

Water Exercise 38

Solution 3

(i) – (a) Water cycle

(ii) – (b) Equator

(iii) – (a)

Solution 4

(i) – (a) Largest lake

(ii) – (b) Periodic rise and fall of water

(iii) - (c) Strong seismic waves

(iv) - (d) Streams of water moving along definite paths