#### NCERT Solutions for Class 11th: Ch 13 Water

Exercises

Page No. 118

1. Multiple choice questions.

(i) Identify the element which is not a part of the hydrological cycle
(a) Evaporation
(b) Hydration
(c) Precipitation
(d) Condensation
► (b) Hydration

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(ii) The average depth of continental slope varies between
(a) 2-20m
(b) 200-2,000m
(c) 20-200m
(d) 2,000-20,000m
► (b) 200-2,000m

(iii) Which one of the following is not a minor relief feature in the oceans:
(a) Seamount
(b) Atoll
(c) Oceanic Deep
(d) Guyot
► (b) Atoll

(iv) Salinity is expressed as the amount of salt in grams dissolved in sea water per
(a) 10 gm
(b) 1,000 gm
(c) 100 gm
(d) 10,000 gm
► (b) 1,000 gm

(v) Which one of the following is the smallest ocean:
(a) Indian Ocean
(b) Arctic Ocean
(c) Atlantic Ocean
(d) Pacific Ocean
► (b) Arctic Ocean

(i) Why do we call the earth a Blue Planet?

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) What is a continental margin?

The continental slope together with the continental shelf is called the continental margin.

(iii) List out the deepest trenches of various oceans.

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) What is a thermocline?

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 you move into the ocean what thermal layers would you encounter? Why the temperature varies with depth?

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 500m thick with temperatures ranging between 20° and 25° C. The second layer is 500 -1,000 m thick. The third layer is very cold and extends upto the deep ocean floor

(vi) What is salinity of sea water?

Salinity is the term used to define the total content of dissolved salts in sea water . 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.

(i) How are various elements of the hydrological cycle interrelated?

Water is a cyclic resource. It can be used and re-used. 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 between the oceans, atmosphere, landsurface 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 per cent ofthe planetary water is found in the oceans. The remaining is held as freshwater in glaciers and icecaps, groundwater 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) Examine the factors that influence the temperature distribution of the oceans.

The factors which affect the distribution of temperature of ocean water are :

(i) 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 form 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.

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