NCERT Solutions for Class 11 Geography (Fundamental of physical geography) Chapter 12 Water (Oceans)

NCERT
SOLUTIONS
CLASS - 11th

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 13 Social Science Geography

Class : 11th

Subject : Geography

Chapter : 13

Chapter Name : Water (Oceans)

Q1 Multiple choice questions.

(i) Identify the element which is not a part of the hydrological cycle

(a) Evaporation

(b) Hydration

(c) Precipitation

(d) Condensation

(ii) The average depth of continental slope varies between

(a) 2-20m

(b) 200-2,000m

(c) 20-200m

(d) 2,000-20,000m

(iii) Which one of the following is not a minor relief feature in the oceans:

(a) Seamount

(b) Atoll

(c) Oceanic Deep

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 13 Social Science Geography

(d) Guyot

(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

(v) Which one of the following is the smallest ocean:

(a) Indian Ocean

(b) Arctic Ocean

(c) Atlantic Ocean

(d) Pacific Ocean

Answer.(i) (b) Hydration

(ii) (b) 200-2,000m

(iii) (d) Oceanic Deep

(iv) (b) 1,000 gm

(v) (b) Arctic Ocean

Page : 115 , Block Name : Multiple Choice Questions

Q2 Answer the following questions in about 30 words.

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 13 Social Science Geography

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

(ii) What is a continental margin?

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

(iv) What is a thermocline?

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

(vi) What is salinity of sea water?

Answer.

(i) Water is an essential component of all life forms that exist over the surface of the earth.
Water is a rare commodity in our solar system. There is no water on the sun or anywhere else in
the solar system. The earth, fortunately has an abundant supply of water on its surface. Hence,
earth is called the ‘Blue Planet’.

(ii) The continental margin is the shallow water area found in proximity to the continent. The
continental margin consists of three different features :-

➔​ ​Continental rise

➔​ ​Continental slope

➔​ ​Continental shelf

Continental margins constitute about 28% of the oceanic area. The continental margin is the
extended portion of each continent occupied by relatively shallow seas and gulfs. It is the
shallowest part of the ocean showing an average gradient of 1° or even less.

(iii) 57 trenches have been explored so far ,of which 32 trenches are there in the Pacific Ocean;
19 trenches are there in the Atlantic Ocean and 6 trenches are there in the Indian Ocean. Some
important trenches of the world are :-

➔​ ​Mariana Trench

➔​ ​Puerto Rico Trench

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 13 Social Science Geography

➔​ ​Sunda Trench

➔​ ​Tonga Trench

➔​ ​Philippine Trench

➔​ ​Kuril- Kamchatka Trench

➔​ ​Kermadec Trench

➔​ ​Izu-Ogasawara Trench

➔​ ​South Sandwich Trench

➔​ ​Peru–Chile Trench

(iv) The temperature-depth profile for the ocean water shows that the temperature decreases
with increasing depth. The profile shows a boundary region between the surface waters of the
ocean and the deeper layers. The boundary usually begins around 100 - 400 m below the sea
surface and extends several hundred metres downward. This boundary region, where there is a
rapid decrease of temperature, is called the thermocline. About 90 per cent of the total volume
of water is found below the thermocline in the deep ocean. In this zone, temperatures approach
0° C.

(v) The temperature structure of oceans is a three-layer system from surface to the bottom.

➔​ ​The first layer represents the top layer of warm oceanic water and it is about 500m
thick with temperatures ranging between 20° and 25° C. This layer, within the tropical
region, is present throughout the year but in mid latitudes it develops only during
summer.

➔​ ​The second layer called the thermocline layer lies below the first layer and is
characterised by rapid decrease in temperature with increasing depth. The thermocline
is 500 -1,000 m thick.

➔​ ​The third layer is very cold and extends upto the deep ocean floor. In the Arctic and
Antarctic circles, the surface water temperatures are close to 0° C and so the
temperature change with the depth is very slight. Here, only one layer of cold water
exists, which extends from surface to deep ocean floor.

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 13 Social Science Geography

The temperature of the ocean decreases as we go deeper due to the lack of thermal radiation
from the sun. Water is generally incompressible. Thus, we cannot increase the intra-molecular
collisions by applying pressure to water. Therefore the lack of thermal radiation far outweighs
the increased pressure with respect to temperature.

(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.

Page : 115 , Block Name : Short Answer Question

Q3 Answer the following questions in about 150 words.

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

(ii) Examine the factors that influence the temperature distribution of the oceans.

Answer.

(i) Water is a cyclic resource. Water undergoes a cycle from the ocean to land and land to
ocean. The hydrological cycle is the circulation of water within the earth’s hydrosphere in
different forms i.e. the liquid, solid and gaseous phases. It also refers to the continuous
exchange of water between the oceans,atmosphere, land surface and subsurface and the
organisms. About 71 per cent of the 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 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 glaciers.
Various elements of the hydrological cycle can be said to interrelated since water cycle involves
continuation circulation of water from land to air to land again and so on. The whole water cycle
will disappear if one of the stage or element of the water cycle disappear. For example
precipitation of water from air to land will not take place if there is no evaporation or
condensation in the 2 stages of the Hydrological cycle. .

Thus, all the elements of the hydrological cycle are interrelated.

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 13 Social Science Geography

Fig. Hydrological Cycle

(ii) The factors which affect the distribution of temperature of ocean water are :-

➔​ ​Latitude : The temperature of surface water decreases from the equator towards the
poles because the amount of insolation decreases poleward.

➔​ ​Unequal distribution of land and water : Oceans in the northern hemisphere receive
more heat due to their contact with larger extent of land than the oceans in the southern
hemisphere.

➔​ ​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.The onshore winds pile up warm
water near the coast and this raises the temperature.

➔​ ​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.

Page : 115 , Block Name : Long Answer Question

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