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Chapter 11

Hydrosphere

Class 9 - Total Geography Morning Star


Short Answer Questions

Question 1

Name any two ways in which movement of ocean water takes place.

Answer

Two ways in which movement of ocean water takes place are-

  1. Waves
  2. Currents

Question 2

What are tides? Name one factor that causes tides.

Answer

The rise and fall of sea water due to gravitational forces of the sun and the moon are called tides.

Tides are caused by the gravitational forces of the sun and moon.

Question 3

What is the time interval between tides? Name the factors responsible for this time interval.

Answer

A particular tide centre takes 24 hours 52 minutes to come under the moon but by the time there is another tide at the opposite side of the referred tide centre and this happens after 12 hours 26 minutes.

The factors responsible for this time interval are the rotation of the earth and the rotation and revolution of the moon.

Question 4

What are Spring and Neap tides?

Answer

Very high tide is caused when the sun, the moon and the earth are almost in the same line. Such high tides are called spring tides.

On the seventh or eighth day of every fortnight of a month, the sun, the earth and the moon come in the position of quadrature. The tide producing forces of the sun and the moon work in opposite direction, with the result, a low tide occurs. Such a tide, which is lower in height than that of a normal tide, is called neap tide.

Question 5

Name two types of ocean currents based on their temperature. Give an example of each.

Answer

Two types of ocean currents based on their temperature are-

  1. The Warm Currents, e.g. Gulf Stream
  2. The Cold Currents, e.g. Labrador current

Question 6

For what is the Gulf Stream famous?

Answer

The Gulf Stream is a powerful warm ocean current affecting the climate of east coast of North America and west coast of Europe. It is also a potential source of renewable power generation.

Question 7

What happens when warm and cold currents meet?

Answer

The combination of warm and cold currents produces heavy fogs and creates rich fishing grounds.

Structured Questions

Question 1(a)

How are tides formed?

Answer

The tides have their origin in the gravitational forces of the sun and the moon.

When the sun, the earth and the moon are in the same line, their gravitational forces work together and high tides are formed.

When the sun and the moon are at the position of right angle with reference to the earth, the gravitational forces of the sun and the moon work against each other and hence, low tides are formed.

Question 1(b)

Differentiate between High Tides and Low Tides.

Answer

High TidesLow Tides
High water level during a tide is known as high tide.Low water level during a tide is called low tide.
The sun, the earth and the moon are in the same line.The sun and the moon are at the position of right angle with reference to the earth.
Gravitational forces of the sun and the moon work together.Gravitational forces of the sun and the moon work against each other.

Question 1(c)

Give a reason for each of the following:

(i) There are two high and two low tides in a day.

(ii) Each day a tide is delayed by 26 minutes.

(iii) The tidal range differs from one water body to the other.

Answer

(i) Because the Earth rotates through two tidal bulges every lunar day, coastal areas experience two high and two low tides every 24 hours and 52 minutes. This occurs because the moon is revolving around the Earth in the same direction as the Earth is rotating on its axis.

(ii) Each day a tide is delayed by 26 minutes because the moon also rotates on its axis while revolving around the earth. Since the earth rotates from west to east the tide centre shifts westwards. When the tide centre completes one round, the moon's position is ahead of the tide centre by that time. This delays the tide by 26 minutes each day.

(iii) The tidal range differs from one water body to the other as tidal range is not constant but changes depending on the locations of the moon and the sun.

Question 1(d)

Draw a well labelled diagram showing the formation of spring and neap tides.

Answer

Below diagram shows the formation of spring and neap tides:

Draw a well labelled diagram showing the formation of spring and neap tides. Hydrosphere, Total Geography Solutions ICSE Class 9.

Question 2(a)

Describe the two types of ocean currents based on their temperature.

Answer

The two types of ocean currents based on their temperature are-

1. The Warm Current — These are those currents which flow from the low latitudes in Tropical Zones towards the high latitudes in the Temperate and sub-polar zones. They bring warm water into cold water areas. For example, Gulf Stream.

2. The Cold Current — These currents have a lower surface temperature and bring cold water into warm water areas. These currents flow in the high latitudes from the Polar regions towards the low latitudes in the warm Equator region. For example, Labrador current.

Question 2(b)

State any two factors responsible for causing the currents.

Answer

Two factors responsible for causing the currents are-

  1. Level of Salinity
  2. Temperature

Question 2(c)

Give a reason for each of the following:

(i) Warm currents produce a milder climate.

(ii) The eastern coasts of USA are comparatively cold.

(iii) The coasts of Norway are not frozen in winter whereas its adjoining coasts are frozen for most parts of the year.

Answer

(i) Warm currents produce a milder climate because warm currents tend to raise the temperature of the places where they flow.

(ii)The eastern coast of US is comparatively cold because of the cold Labrador Current.

(iii) The coasts of Norway are not frozen in winter whereas its adjoining coasts are frozen for most parts of the year on account of the influence of the warm North Atlantic Drift.

Question 2(d)

Describe one effect of each of the following three ocean currents.

(i) Labrador Current of the Atlantic Ocean.

(ii) The Kuroshio current

(iii) Oyashio Current of the Pacific Ocean.

Answer

(i) The waters of the Labrador current have a cooling effect on the Canadian Atlantic provinces and coastal New England.

(ii) The warm waters of the Kuroshio current sustain the coral reefs in the world.

(iii) Oyashio current has an important impact on the climate of the Russian Far East, mainly in Kamchatka and Chukotka.

Question 3(a)

State the origin and flow of the Gulf Stream.

Answer

Gulf Stream originates in the gulf of Mexico, exits through the Strait of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean. At about 30°W, 40°N, it splits in two, with the northern stream crossing to northern Europe and the southern stream recirculating off West Africa.

Question 3(b)

What is the effect of Gulf Stream on the coasts of North America and Western Europe?

Answer

The Gulf Stream influences the climate of the east coast of North America from FLorida to Newfoundland, and the west coast of Europe. The current keeps these regions warm in winter.

Question 3(c)

Give a reason for each of the following:

(i) The waters of the Oyashio Current form the richest fishing grounds in the world.

(ii) There is heavy rainfall in Queensland but the Atacama desert is arid.

(iii) Rich fishing grounds are located on the Pacific coast of North America.

Answer

(i) The waters of the Oyashio Current form the richest fishing grounds in the world owing to the extremely high nutrient content of the cold water and the very high tides in some areas, which further enhances the availability of nutrients.

(ii) Warm currents flow towards Queensland which make the air warm and enable it to acquire greater moisture. Thus, the winds increase the amount of precipitation in Queensland while Atacama desert owe their existence to some extent to Benguela and Peru currents which are cold and keep the air dry and devoid of moisture.

(iii) Rich fishing grounds are located on the Pacific coast of North America due to the convergence of warm and cold currents.

Question 3(d)

Describe three major effects of currents.

Answer

Three major effects of currents are-

1. Effect on Climate — The climate of the coasts becomes warm or cool according to the current washing the coast which may be warm or cool.

2. Effect on Marine life — Ocean currents move organic material off the coast which is the food of planktons. The more the planktons, higher the concentration of fish.

3. Effect on commerce — On account of influence of warm currents, harbours are kept open in winter, facilitating trade throughout the year.

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