Selina Textbook Solutions: Hydrosphere | Geography Class 9 ICSE PDF Download

 Page 1


Hydrosphere 
Exercises 
I. Short Answer Questions 
Question 1. 
Name the three ways in which movement of ocean water takes place. 
Answer: 
Oceanic water movement is affected by the rotation of the earth e.g. earth’s movement 
from west to east compels water to move from east to west as North and South 
equatorial current along with a contour equatorial current. Secondly, the direction of 
planetary winds motivates currents as the trade winds push forcefully towards 
polewards and afterwards by the Westerlies towards North East as warm currents 
touching North American eastern and European Western coast. Thirdly, the level of 
salinity makes the water to move less saline water to move saline water. 
Question 2. 
What are tides ? Name one factor that causes tides. 
Answer: 
Tides are the rise and fall of sea water due to gravitational forces of the sun and the 
moon. Tides are mainly caused by the centrifugal and centripetal forces of the earth and 
the moon. 
Question 3. 
What is the time interval between tides ? Name the factors responsible for this time 
interval ? 
Answer: 
On account of the continuous rotation of the earth and revolution of the moon around 
the earth, whenever the moon comes in the front of the earth, tide takes place at an 
interval of 24 hours and 52 minutes and at the same time on the opposite side of the 
earth the interval is of 12 hours and 26 minutes. 
Question 4. 
What are Spring and Neap tides ? 
Answer: 
When the gravitational forces of the sun and the moon work together to attract the earth 
due to being in a straight line, high tides or Spring tides are caused. When the sun and 
the moon are in right angle with respect to the earth, Neap tides or low tides are 
caused. 
 
Page 2


Hydrosphere 
Exercises 
I. Short Answer Questions 
Question 1. 
Name the three ways in which movement of ocean water takes place. 
Answer: 
Oceanic water movement is affected by the rotation of the earth e.g. earth’s movement 
from west to east compels water to move from east to west as North and South 
equatorial current along with a contour equatorial current. Secondly, the direction of 
planetary winds motivates currents as the trade winds push forcefully towards 
polewards and afterwards by the Westerlies towards North East as warm currents 
touching North American eastern and European Western coast. Thirdly, the level of 
salinity makes the water to move less saline water to move saline water. 
Question 2. 
What are tides ? Name one factor that causes tides. 
Answer: 
Tides are the rise and fall of sea water due to gravitational forces of the sun and the 
moon. Tides are mainly caused by the centrifugal and centripetal forces of the earth and 
the moon. 
Question 3. 
What is the time interval between tides ? Name the factors responsible for this time 
interval ? 
Answer: 
On account of the continuous rotation of the earth and revolution of the moon around 
the earth, whenever the moon comes in the front of the earth, tide takes place at an 
interval of 24 hours and 52 minutes and at the same time on the opposite side of the 
earth the interval is of 12 hours and 26 minutes. 
Question 4. 
What are Spring and Neap tides ? 
Answer: 
When the gravitational forces of the sun and the moon work together to attract the earth 
due to being in a straight line, high tides or Spring tides are caused. When the sun and 
the moon are in right angle with respect to the earth, Neap tides or low tides are 
caused. 
 
Question 5. 
Name two types of ocean currents based on their temperature. 
Answer: 
There are two types of ocean currents e.g., warm and cold currents. The current which 
flows from warm tropical region to cooler temperate and polar region is called warm 
current and the current flowing from polar areas towards temperate and equational 
regions is called cold current, e.g. Gulf stream is a warm current and Labrador current is 
called cold current. 
Question 6. 
For what is the Gulf Stream famous? 
Answer: 
The Gulf Stream is a powerful warm ocean current affecting the climate of eastern coast 
of North America and western coast of Europe and it is an important source of tidal 
energy. 
Question 7. 
What happens when warm and cold currents meet ? 
Answer: 
By meeting the warm and cold currents, large amount of fog is created, which controls 
the temperature conditions in the fishing regions of the meeting grounds. 
Question 8. 
What is meant by ‘salinity’ of ocean water ? 
Answer: 
Salinity is the amount of sodium in the oceanic water. It is 35%. 
Question 9. 
Name the factors responsible for subsurface movement of ocean waters. 
Answer: 
The factors responsible for ocean currents are the rotation of the earth, difference in 
salinity, temperature and the prevailing winds. 
Question 10. 
State the relationship between temperature and density of ocean water. 
Answer: 
High temperature near the equatorial belt and landlocked seas leads to higher salinity or 
higher density of ocean water. 
Question 11. 
State one difference between waves and tides. 
Answer: 
Waves are the oscillatory (to and fro) movements in the oceanic water, but tides are 
particular turbulent motion of the oceanic water due to gravitational forces (centrifugal 
Page 3


Hydrosphere 
Exercises 
I. Short Answer Questions 
Question 1. 
Name the three ways in which movement of ocean water takes place. 
Answer: 
Oceanic water movement is affected by the rotation of the earth e.g. earth’s movement 
from west to east compels water to move from east to west as North and South 
equatorial current along with a contour equatorial current. Secondly, the direction of 
planetary winds motivates currents as the trade winds push forcefully towards 
polewards and afterwards by the Westerlies towards North East as warm currents 
touching North American eastern and European Western coast. Thirdly, the level of 
salinity makes the water to move less saline water to move saline water. 
Question 2. 
What are tides ? Name one factor that causes tides. 
Answer: 
Tides are the rise and fall of sea water due to gravitational forces of the sun and the 
moon. Tides are mainly caused by the centrifugal and centripetal forces of the earth and 
the moon. 
Question 3. 
What is the time interval between tides ? Name the factors responsible for this time 
interval ? 
Answer: 
On account of the continuous rotation of the earth and revolution of the moon around 
the earth, whenever the moon comes in the front of the earth, tide takes place at an 
interval of 24 hours and 52 minutes and at the same time on the opposite side of the 
earth the interval is of 12 hours and 26 minutes. 
Question 4. 
What are Spring and Neap tides ? 
Answer: 
When the gravitational forces of the sun and the moon work together to attract the earth 
due to being in a straight line, high tides or Spring tides are caused. When the sun and 
the moon are in right angle with respect to the earth, Neap tides or low tides are 
caused. 
 
Question 5. 
Name two types of ocean currents based on their temperature. 
Answer: 
There are two types of ocean currents e.g., warm and cold currents. The current which 
flows from warm tropical region to cooler temperate and polar region is called warm 
current and the current flowing from polar areas towards temperate and equational 
regions is called cold current, e.g. Gulf stream is a warm current and Labrador current is 
called cold current. 
Question 6. 
For what is the Gulf Stream famous? 
Answer: 
The Gulf Stream is a powerful warm ocean current affecting the climate of eastern coast 
of North America and western coast of Europe and it is an important source of tidal 
energy. 
Question 7. 
What happens when warm and cold currents meet ? 
Answer: 
By meeting the warm and cold currents, large amount of fog is created, which controls 
the temperature conditions in the fishing regions of the meeting grounds. 
Question 8. 
What is meant by ‘salinity’ of ocean water ? 
Answer: 
Salinity is the amount of sodium in the oceanic water. It is 35%. 
Question 9. 
Name the factors responsible for subsurface movement of ocean waters. 
Answer: 
The factors responsible for ocean currents are the rotation of the earth, difference in 
salinity, temperature and the prevailing winds. 
Question 10. 
State the relationship between temperature and density of ocean water. 
Answer: 
High temperature near the equatorial belt and landlocked seas leads to higher salinity or 
higher density of ocean water. 
Question 11. 
State one difference between waves and tides. 
Answer: 
Waves are the oscillatory (to and fro) movements in the oceanic water, but tides are 
particular turbulent motion of the oceanic water due to gravitational forces (centrifugal 
and centripital) working together with the earth and the moon which makes the waves of 
the ocean jumping upto several metres resulting in a typical phenomenon of violent 
waves i.e. tides. 
Question 12. 
How do evaporation and precipitation cause movement of ocean water. 
Answer: 
High amount of evaporation increases salinity of oceapic water and excess of 
precipitation makes water less saline. So the heavy saline water sinks down and the 
lighter water flows towards it to take its place as ocean current. 
Question 13. 
How is the rotation of the earth responsible for influencing the direction of currents ? 
Answer: 
The earth rotates from west to east. So, according to the first Law of Motion, the ocean 
currents start to flow from east to west as opposite direction, e.g. the North and South 
Equatorial currents flow from east to west. 
Question 14. 
Name the factors originating within the sea which cause ocean currents. 
Answer: 
The amount of salinity in the oceans in different parts is quite different. So the more 
saline water start to sink downwards and the less saline water runs to take its place on 
the surface, e.g., the ocean current flows from Atlantic ocean towards the 
Mediterranean sea. 
II. Give reasons for the following 
Question 1. 
There are two high and two low tides in a day. 
Answer: 
The rotation of the Earth results in every meridian coming into the position of two high 
tides and two low tides very nearly every 24 hours. 
Question 2. 
Each day a tide is delayed by 26 minutes. 
Answer: 
Each day a tide is delayed by 26 minutes because the moon also rotates on its axis 
(west to east) while revolving round the earth. Since the earth rotates from west to east, 
the tide centre shifts westward. When the tide centre completes one round, the moon’s 
position is ahead of the tide centre by that time. The moon also revolves round the 
earth, with the result, the tide centre takes another 52 minutes to come under the moon. 
Thus, a particular tide centre takes 24 hours 52 minutes to come under the moon but by 
Page 4


Hydrosphere 
Exercises 
I. Short Answer Questions 
Question 1. 
Name the three ways in which movement of ocean water takes place. 
Answer: 
Oceanic water movement is affected by the rotation of the earth e.g. earth’s movement 
from west to east compels water to move from east to west as North and South 
equatorial current along with a contour equatorial current. Secondly, the direction of 
planetary winds motivates currents as the trade winds push forcefully towards 
polewards and afterwards by the Westerlies towards North East as warm currents 
touching North American eastern and European Western coast. Thirdly, the level of 
salinity makes the water to move less saline water to move saline water. 
Question 2. 
What are tides ? Name one factor that causes tides. 
Answer: 
Tides are the rise and fall of sea water due to gravitational forces of the sun and the 
moon. Tides are mainly caused by the centrifugal and centripetal forces of the earth and 
the moon. 
Question 3. 
What is the time interval between tides ? Name the factors responsible for this time 
interval ? 
Answer: 
On account of the continuous rotation of the earth and revolution of the moon around 
the earth, whenever the moon comes in the front of the earth, tide takes place at an 
interval of 24 hours and 52 minutes and at the same time on the opposite side of the 
earth the interval is of 12 hours and 26 minutes. 
Question 4. 
What are Spring and Neap tides ? 
Answer: 
When the gravitational forces of the sun and the moon work together to attract the earth 
due to being in a straight line, high tides or Spring tides are caused. When the sun and 
the moon are in right angle with respect to the earth, Neap tides or low tides are 
caused. 
 
Question 5. 
Name two types of ocean currents based on their temperature. 
Answer: 
There are two types of ocean currents e.g., warm and cold currents. The current which 
flows from warm tropical region to cooler temperate and polar region is called warm 
current and the current flowing from polar areas towards temperate and equational 
regions is called cold current, e.g. Gulf stream is a warm current and Labrador current is 
called cold current. 
Question 6. 
For what is the Gulf Stream famous? 
Answer: 
The Gulf Stream is a powerful warm ocean current affecting the climate of eastern coast 
of North America and western coast of Europe and it is an important source of tidal 
energy. 
Question 7. 
What happens when warm and cold currents meet ? 
Answer: 
By meeting the warm and cold currents, large amount of fog is created, which controls 
the temperature conditions in the fishing regions of the meeting grounds. 
Question 8. 
What is meant by ‘salinity’ of ocean water ? 
Answer: 
Salinity is the amount of sodium in the oceanic water. It is 35%. 
Question 9. 
Name the factors responsible for subsurface movement of ocean waters. 
Answer: 
The factors responsible for ocean currents are the rotation of the earth, difference in 
salinity, temperature and the prevailing winds. 
Question 10. 
State the relationship between temperature and density of ocean water. 
Answer: 
High temperature near the equatorial belt and landlocked seas leads to higher salinity or 
higher density of ocean water. 
Question 11. 
State one difference between waves and tides. 
Answer: 
Waves are the oscillatory (to and fro) movements in the oceanic water, but tides are 
particular turbulent motion of the oceanic water due to gravitational forces (centrifugal 
and centripital) working together with the earth and the moon which makes the waves of 
the ocean jumping upto several metres resulting in a typical phenomenon of violent 
waves i.e. tides. 
Question 12. 
How do evaporation and precipitation cause movement of ocean water. 
Answer: 
High amount of evaporation increases salinity of oceapic water and excess of 
precipitation makes water less saline. So the heavy saline water sinks down and the 
lighter water flows towards it to take its place as ocean current. 
Question 13. 
How is the rotation of the earth responsible for influencing the direction of currents ? 
Answer: 
The earth rotates from west to east. So, according to the first Law of Motion, the ocean 
currents start to flow from east to west as opposite direction, e.g. the North and South 
Equatorial currents flow from east to west. 
Question 14. 
Name the factors originating within the sea which cause ocean currents. 
Answer: 
The amount of salinity in the oceans in different parts is quite different. So the more 
saline water start to sink downwards and the less saline water runs to take its place on 
the surface, e.g., the ocean current flows from Atlantic ocean towards the 
Mediterranean sea. 
II. Give reasons for the following 
Question 1. 
There are two high and two low tides in a day. 
Answer: 
The rotation of the Earth results in every meridian coming into the position of two high 
tides and two low tides very nearly every 24 hours. 
Question 2. 
Each day a tide is delayed by 26 minutes. 
Answer: 
Each day a tide is delayed by 26 minutes because the moon also rotates on its axis 
(west to east) while revolving round the earth. Since the earth rotates from west to east, 
the tide centre shifts westward. When the tide centre completes one round, the moon’s 
position is ahead of the tide centre by that time. The moon also revolves round the 
earth, with the result, the tide centre takes another 52 minutes to come under the moon. 
Thus, a particular tide centre takes 24 hours 52 minutes to come under the moon but by 
that time there is another tide at the opposite side of the referred tide centre and this 
happens after 12 hours 26 minutes. 
Question 3. 
Warm currents produce a milder climate. 
Answer: 
Warm currents of Gulf Stream has made the climate of eastern North America and 
Western Europe mild and pleasant for ideal industrial life and developed oceanic routes 
for trade. In the same way warm Kurosio current has made Japan a progressive country 
by leading in fishing occupation supporting the economy of Japan, Apart from this 
violent storms also follow the meeting places of warm and cold currents, e.g., 
Hurricanes in America and typhoons in China and Japan. 
Question 4. 
The eastern coasts of USA are comparatively cold. 
Answer: 
Due to the cooling effect of Labrador current keeps these coasts comparatively cold. 
Question 5. 
The waters of the Oyashio Current form the richest fishing grounds in the world. 
Answer: 
Due to meeting with warm Kurosio current creates large amount of fog regulating the 
ideal temperature for fish and the remarkable efforts of Japanese for fishing occupation 
makes this region the leading fishing grounds of the world. 
Question 6. 
There is heavy rainfall in Queensland but the Atacama desert is arid. 
Answer: 
Queensland’s coast is touched by the warm east Australian current and gets heavy 
rainfall by trade winds from sea towards land, but Atacama desert is touched by cold 
Peruvian current and the westerlies blowing from land towards sea make Atacama the 
cold driest desert in the world. 
Question 7. 
The coasts of Norway are not frozen in winter whereas its adjoining coasts are frozen 
for most parts of the year. 
Answer: 
The Western coast of Norway are not frozen in winter due to the warm effect of Gulf 
Stream or the North Atlantic Drift touching the coast. 
 
 
Page 5


Hydrosphere 
Exercises 
I. Short Answer Questions 
Question 1. 
Name the three ways in which movement of ocean water takes place. 
Answer: 
Oceanic water movement is affected by the rotation of the earth e.g. earth’s movement 
from west to east compels water to move from east to west as North and South 
equatorial current along with a contour equatorial current. Secondly, the direction of 
planetary winds motivates currents as the trade winds push forcefully towards 
polewards and afterwards by the Westerlies towards North East as warm currents 
touching North American eastern and European Western coast. Thirdly, the level of 
salinity makes the water to move less saline water to move saline water. 
Question 2. 
What are tides ? Name one factor that causes tides. 
Answer: 
Tides are the rise and fall of sea water due to gravitational forces of the sun and the 
moon. Tides are mainly caused by the centrifugal and centripetal forces of the earth and 
the moon. 
Question 3. 
What is the time interval between tides ? Name the factors responsible for this time 
interval ? 
Answer: 
On account of the continuous rotation of the earth and revolution of the moon around 
the earth, whenever the moon comes in the front of the earth, tide takes place at an 
interval of 24 hours and 52 minutes and at the same time on the opposite side of the 
earth the interval is of 12 hours and 26 minutes. 
Question 4. 
What are Spring and Neap tides ? 
Answer: 
When the gravitational forces of the sun and the moon work together to attract the earth 
due to being in a straight line, high tides or Spring tides are caused. When the sun and 
the moon are in right angle with respect to the earth, Neap tides or low tides are 
caused. 
 
Question 5. 
Name two types of ocean currents based on their temperature. 
Answer: 
There are two types of ocean currents e.g., warm and cold currents. The current which 
flows from warm tropical region to cooler temperate and polar region is called warm 
current and the current flowing from polar areas towards temperate and equational 
regions is called cold current, e.g. Gulf stream is a warm current and Labrador current is 
called cold current. 
Question 6. 
For what is the Gulf Stream famous? 
Answer: 
The Gulf Stream is a powerful warm ocean current affecting the climate of eastern coast 
of North America and western coast of Europe and it is an important source of tidal 
energy. 
Question 7. 
What happens when warm and cold currents meet ? 
Answer: 
By meeting the warm and cold currents, large amount of fog is created, which controls 
the temperature conditions in the fishing regions of the meeting grounds. 
Question 8. 
What is meant by ‘salinity’ of ocean water ? 
Answer: 
Salinity is the amount of sodium in the oceanic water. It is 35%. 
Question 9. 
Name the factors responsible for subsurface movement of ocean waters. 
Answer: 
The factors responsible for ocean currents are the rotation of the earth, difference in 
salinity, temperature and the prevailing winds. 
Question 10. 
State the relationship between temperature and density of ocean water. 
Answer: 
High temperature near the equatorial belt and landlocked seas leads to higher salinity or 
higher density of ocean water. 
Question 11. 
State one difference between waves and tides. 
Answer: 
Waves are the oscillatory (to and fro) movements in the oceanic water, but tides are 
particular turbulent motion of the oceanic water due to gravitational forces (centrifugal 
and centripital) working together with the earth and the moon which makes the waves of 
the ocean jumping upto several metres resulting in a typical phenomenon of violent 
waves i.e. tides. 
Question 12. 
How do evaporation and precipitation cause movement of ocean water. 
Answer: 
High amount of evaporation increases salinity of oceapic water and excess of 
precipitation makes water less saline. So the heavy saline water sinks down and the 
lighter water flows towards it to take its place as ocean current. 
Question 13. 
How is the rotation of the earth responsible for influencing the direction of currents ? 
Answer: 
The earth rotates from west to east. So, according to the first Law of Motion, the ocean 
currents start to flow from east to west as opposite direction, e.g. the North and South 
Equatorial currents flow from east to west. 
Question 14. 
Name the factors originating within the sea which cause ocean currents. 
Answer: 
The amount of salinity in the oceans in different parts is quite different. So the more 
saline water start to sink downwards and the less saline water runs to take its place on 
the surface, e.g., the ocean current flows from Atlantic ocean towards the 
Mediterranean sea. 
II. Give reasons for the following 
Question 1. 
There are two high and two low tides in a day. 
Answer: 
The rotation of the Earth results in every meridian coming into the position of two high 
tides and two low tides very nearly every 24 hours. 
Question 2. 
Each day a tide is delayed by 26 minutes. 
Answer: 
Each day a tide is delayed by 26 minutes because the moon also rotates on its axis 
(west to east) while revolving round the earth. Since the earth rotates from west to east, 
the tide centre shifts westward. When the tide centre completes one round, the moon’s 
position is ahead of the tide centre by that time. The moon also revolves round the 
earth, with the result, the tide centre takes another 52 minutes to come under the moon. 
Thus, a particular tide centre takes 24 hours 52 minutes to come under the moon but by 
that time there is another tide at the opposite side of the referred tide centre and this 
happens after 12 hours 26 minutes. 
Question 3. 
Warm currents produce a milder climate. 
Answer: 
Warm currents of Gulf Stream has made the climate of eastern North America and 
Western Europe mild and pleasant for ideal industrial life and developed oceanic routes 
for trade. In the same way warm Kurosio current has made Japan a progressive country 
by leading in fishing occupation supporting the economy of Japan, Apart from this 
violent storms also follow the meeting places of warm and cold currents, e.g., 
Hurricanes in America and typhoons in China and Japan. 
Question 4. 
The eastern coasts of USA are comparatively cold. 
Answer: 
Due to the cooling effect of Labrador current keeps these coasts comparatively cold. 
Question 5. 
The waters of the Oyashio Current form the richest fishing grounds in the world. 
Answer: 
Due to meeting with warm Kurosio current creates large amount of fog regulating the 
ideal temperature for fish and the remarkable efforts of Japanese for fishing occupation 
makes this region the leading fishing grounds of the world. 
Question 6. 
There is heavy rainfall in Queensland but the Atacama desert is arid. 
Answer: 
Queensland’s coast is touched by the warm east Australian current and gets heavy 
rainfall by trade winds from sea towards land, but Atacama desert is touched by cold 
Peruvian current and the westerlies blowing from land towards sea make Atacama the 
cold driest desert in the world. 
Question 7. 
The coasts of Norway are not frozen in winter whereas its adjoining coasts are frozen 
for most parts of the year. 
Answer: 
The Western coast of Norway are not frozen in winter due to the warm effect of Gulf 
Stream or the North Atlantic Drift touching the coast. 
 
 
Question 8. 
Rich fishing grounds are located on the Pacific coast of North America. 
Answer: 
The Pacific coast of North America affected by the warm Kurosio current are the famous 
fishing grounds of salmon fish mainly shared by Canada. 
III. Long Answer Questions 
PQ. Differentiate between the three movements of ocean water-waves, tides and 
currents. 
Answer: 
Waves are oscillatory movement in water, manifested by an alternate rise and fall of the 
sea surface. Every wave has a wavelength, velocity, height and wave period. The rise 
and fall of sea water due to gravitational forces of the sun and the moon are called 
tides. The sea waves produced by tides are called tidal waves. Ocean currents are 
large masses of surface water that circulate in regular patterns around the ocean. It is of 
two types warm and the cold. 
Question 1. 
Discuss the origin of tides. Illustrate the formation of Spring Tides. 
Answer: 
The tides have their origin in the gravitational forces of the sun and the moon. The earth 
rotates from west to east and revolves round the sun following an elliptical orbit. 
Similarly, the moon, rotates from west to east and revolves round the earth along an 
elliptical orbit. 
Spring Tides : Very high tides are caused when the sun and the moon and the earth 
are almost in the same line. Such high tides are called Spring Tides. The gravitational 
forces of the sun and the moon work together with combined force and thus a high tide 
is caused. The height of such Spring Tides is 20 per cent more than that of the normal 
tides. Such tides take place twice every month (during the full moon and the new moon) 
and their timing is fixed.