NCERT Solutions for Class 11 Geography (Fundamental of physical geography) Chapter 13 Movements of Ocean Water

NCERT
SOLUTIONS
CLASS - 11th

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 14 Social Science Geography

Class : 11th

Subject : Geography

Chapter : 14

Chapter Name : Movements of Ocean Water

Q1 Multiple choice questions.

(i) Upward and downward movement of ocean water is known as the :

(a) tide

(b) current

(c) wave

(d) none of the above

(ii) Spring tides are caused :

(a) As result of the moon and the sun pulling the earth gravitationally in the same direction.

(b) As result of the moon and the sun pulling the earth gravitationally in the opposite direction.
(c) Indention in the coast line.

(d) None of the above.

(iii) The distance between the earth and the moon is minimum when the moon is in :

(a) Aphelion

(b) Perigee

(c) Perihelion

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 14 Social Science Geography

(d) Apogee

(iv) The earth reaches its perihelion in:

(a) October

(b) September

(c) July

(d) January

Answer.

(i) (a) tide

(ii) (a) As result of the moon and the sun pulling the earth gravitationally in the same direction.

(iii) (b) Perigee

(iv) (d) January

Page : 121 , Block Name : Multiple Choice Questions

Q2 Answer the following questions in about 30 words.

(i) What are waves?

(ii) Where do waves in the ocean get their energy from?

(iii) What are tides?

(iv) How are tides caused?

Answer.

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 14 Social Science Geography

(i) Waves are actually the energy, not the water as such, which moves across the ocean
surface. Water particles only travel in a small circle as a wave passes.

(ii) Wind provides energy to the waves. Wind causes waves to travel in the ocean and the
energy is released on shorelines.

(iii) The periodical rise and fall of the sea level, once or twice a day, mainly due to the attraction
of the sun and the moon, is called a tide.

(iv) The moon’s gravitational pull to a great extent and to a lesser extent the sun’s gravitational
pull, are the major causes for the occurrence of tides. Another factor is centrifugal force, which
is the force that acts to counterbalance the gravity. Together, the gravitational pull and
centrifugal force are responsible for creating the two major tidal bulges on the earth.

Page : 121 , Block Name : Short Answer Question

(v) How are tides related to navigation?

Answer. Tides are caused by the earth-moon-sun positions which are known accurately, the
tides can be predicted well in advance. This helps the navigators and fishermen plan their
activities. Tidal heights are very important, especially harbours near rivers and within estuaries
having shallow ‘bars’ at the entrance, which prevent ships and boats from entering into the
harbour.

Page : 121 , Block Name : Short Answer Question

Q3 Answer the following questions in about 150 words.

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 14 Social Science Geography

(i) How do currents affect the temperature? How does it affect the temperature of coastal areas
in the N. W. Europe?

(ii) What are the causes of currents?

Answer.

(i) Ocean currents have a number of direct and indirect influences on human activities. West
coasts of the continents in tropical and subtropical latitudes (except close to the equator) are
bordered by cool waters. Their average temperatures are relatively low with a narrow diurnal
and annual ranges. There is fog, but generally the areas are arid. West coasts of the continents
in the middle and higher latitudes are bordered by warm waters which cause a distinct marine
climate. They are characterised by cool summers and relatively mild winters with a narrower
annual range of temperatures. Warm currents flow parallel to the east coasts of the continents
in tropical and subtropical latitudes. This results in warm and rainy climates. These areas lie in
the western margins of the subtropical anticyclones.

In North West Europe, warm currents exist. They increase the temperature in coastal areas of
N. W. Europe.

(ii) Ocean currents are like river flow in oceans. They represent a regular volume of water in a
definite path and direction. Ocean currents are influenced by two types of forces :-

➔​ ​Primary forces that initiate the movement of water

➔​ ​Secondary forces that influence the currents to flow.

The Primary forces that influence the currents are :-

➔​ ​Heating by solar energy

➔​ ​Wind

➔​ ​Gravity

➔​ ​Coriolis force.

Heating by solar energy causes the water to expand.This causes a very slight gradient and
water tends to flow down the slope. Wind blowing on the surface of the ocean pushes the water
to move. Friction between the wind and the water surface affects the movement of the water
body in its course. Gravity tends to pull the water down the pile and create gradient variation.
The Coriolis force intervenes and causes the water to move to the right in the northern

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Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 14 Social Science Geography

hemisphere and to the left in the southern hemisphere. These produce large circular currents in
all the ocean basins.

Differences in water density affect vertical mobility of ocean currents. Water with high salinity is
denser than water with low salinity and in the same way cold water is denser than warm water.
Denser water tends to sink, while relatively lighter water tends to rise. Cold-water ocean
currents occur when the cold water at the poles sinks and slowly moves towards the equator.
Warm-water currents travel out from the equator along the surface, flowing towards the poles to
replace the sinking cold water.

Page : 121 , Block Name : Long Answer Question

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