NCERT Solutions for Class 11 Geography Chapter 13 Water(Oceans)

Ans : (i) (b) Hydration
(ii) (b) 200-2,000m
(iii) (b) Atoll
(iv) (b) 1,000 gm
(v) (b) Arctic Ocean 

Ans : (i) The earth is called as a Blue Planet because of abundant supply of water on its surface. Water is a rare commodity in our solar system. There is no water on the sun or anywhere else in the solar system.


(ii) The continental slope together with the continental shelf is called the continental margin.


(iii) There are 57 trenches have been explored so far; of which 32 are in the Pacific Ocean; 19 in the Atlantic Ocean and 6 in the Indian Ocean.


(iv) The boundary region, from where there is a rapid decrease of temperature, is called the thermocline.
This layer lies below the first layer and is characterised by rapid decrease in temperature with increasing depth.


(v) When we move into the ocean we will encounter three thermal layers.
The temperature varies with the depth because the temperature structure of oceans over middle and low latitudes can be described as a three layer system. The first layer is about 500 m thick with temperatures ranging beüeen 200 and 250 C. The second layer is 500-1,000 m thick. The third layer is very cold and extends upto the deep ocean floor


(vi) Salinity is the term used to define the total content of dissolved salts in seawater . It is calculated as the amount of salt (in gm) dissolved in 1,000 gm (1 kg) of seawater. It depend mainly on evaporation and precipitation. 

Ans : Water is a cyclic resource. It can be used and reused. The hydrological cycle, is the circulation of water within the earth's hydrosphere in different forms i.e. the liquid, solid and the gaseous phases. It also refers to the continuous exchange of water beüeen the oceans, atmosphere, land surface and subsurface and the organisms. The distribution of water on earth is quite uneven. Many locations have plenty of water while others have very limited quantity. About 71 percent of the planetary water is found in the oceans. The remaining is held as freshwater in glaciers and icecaps, ground.Water sources, lakes, soil moisture, atmosphere, streams and within life. Nearly 59 per cent of the water that falls on land returns to the atmosphere through evaporation from over the oceans as well as from other places. The remainder runs-off on the surface, infiltrates into the ground or a part of it becomes glacier


(ii) The factors which affect the distribution of temperature of ocean water are :
(l) Latitude: The temperature of surface water decreases from the equator towards the poles because the amount of insolation decreases poleward. 
(ii) Unequal distribution of land and water: The oceans in the northern hemisphere receive more heat due to their contact with larger extent of land than the oceans in the southern hemisphere.
(iii) Prevailing wind: The winds blowing from the land towards the oceans drive warm surface water away from the coast resulting in the upwelling of cold water from below. It results into the longitudinal variation in the temperature. Contrary to this, the onshore winds pile up warm water near the coast and this raises the temperature.
(iv) Ocean currents: Warm ocean currents raise the temperature in cold areas while the cold currents decrease the temperature in warm ocean areas. Gulf stream (warm current) raises the temperature near the eastern coast of North America and the West Coast of Europe while the Labrador current (cold current) lowers the temperature near the north-east coast of North America.