WBBSE 10th Class Social Science Solutions Geography & Environment Chapter 3 Hydrosphere
WBBSE 10th Class Social Science Solutions Geography & Environment Chapter 3 Hydrosphere
West Bengal Board 10th Class Social Science Solutions Geography & Environment Chapter 3 Hydrosphere
WBBSE 10th Class Geography & Environment Solutions
TOPIC – 1
Ocean Currents
Long Answer Type Questions
1. Discuss the causes of generation of ocean currents.
OR, Explain how the ocean currents are generated.
Ans. The ocean currents are generated for the following reasons-
- Wind: The planetary winds tend to generate currents in the water of the oceans over which they blow. They push the water in the direction as they blow. Example-In regions under the influence of trade winds, the ocean currents flow from the east towards the west, and in regions under the influence of westerlies, the ocean currents flow from the west towards the east. In this way new ocean currents originate.
- Difference in temperature in oceans: The ocean water in the equatorial and tropical regions is warm and lead to high. rates of evaporation. This warm water is lighter and flow towards the polar regions as surface currents. In order to fill up this vacuum, the cold and heavy water of the oceans in polar regions flow towards the equatorial region. This water being cold and heavy, flow as undercurrents through the deeper layers of the oceans.
- Difference in salinity: The level of salinity in ocean waters is not uniform everywhere. The less saline water is lighter and flow as surface currents towards the more saline water. The more saline water on the other hand, is heavier. It flows as undercurrents towards the less saline water in order to fill the vacuum.
- Rotation of the earth: The ocean currents cannot flow in a straight direction due to the rotation of the earth. According to Ferrel’s Law, the ocean currents are deflected towards the right in the northern hemisphere and towards the left in the southern hemisphere. Example-The Gulf stream turns towards the right and gives rise to the North Atlantic current due to the rotation of the earth.
- Location and shape of continents: The ocean currents follow the coastline of the continents as they flow. In many cases, if they are obstructed by the margin or tip of the continent or some islands, they may give rise to new ocean currents. Example-The South Equatorial current is obstructed by the cape of St. Roch in Brazil, from where a new current called the Brazil current originates.
- Melting of ice: The melting of ice in some regions raise the level of water in the oceans. This water then tends to flow towards the regions with less water in order to maintain a balance. Thus ocean currents are generated.
2. Discuss the effects of ocean currents.
OR, What are the influence of ocean currents on human life?
Ans. The influence of ocean currents on human life are as follows-
- Ice-free ports: The warm currents help to keep the ports of higher latitudes ice-free even in winters. Example- The warm North Atlantic current keeps many Norwegian ports free from ice, so that they can be used throughout the year.
- Help in navigation: The warm currents flowing through the surface of the oceans make sailing of ships easier. This also helps in saving fuel. Hence, ships prefer to follow routes along the path of warm ocean currents.
- Influence on climate: The region lying adjacent to warm currents have warm climate and the region lying adjacent to cold currents have cold or cooler climate. Example-The cold Labrador current keeps the summers in Newfoundland coast cool and the warm Kuroshio current keeps the western coast of Japan warm in winter.
- Rainfall and snowfall: The air blowing over warm currents become warm and collect much water vapour. Thus, they cause heavy rainfall on the coastal areas. But, the air blowing over cold currents are cold and dry. They cause no rainfall, but sometimes cause snowfall in higher latitudes. Example- Namib desert has formed near the south-western coast of Africa in Namibia due to lack of rainfall.
- Rough weather: The regions where warm and cold currents meet experience dense foggy conditions and severe thunderstorms. This hampers the sailing of ships and flying of aeroplanes over the region.
- Development of fishing grounds: A huge amount of planktons grow in regions where warm and cold currents meet. This help in the development of fishing grounds, as planktons are the favourite food of fishes. Example-Coastal regions of Newfoundland and Japan.
- Submerged bars: The icebergs moving with the cold currents melt when they meet the warm currents. Thus, the rocks, pebbles, clay, sand, etc., trapped within the icebergs get deposited on the continental shelves. These gradually accumulate and rise in height and lead to the formation of submerged sandbars. These develop as very good fishing grounds.
- Danger of icebergs: The cold currents bring down icebergs along with them from high latitude to low latitude regions. These pose a threat to ships that sail along those routes. Example-The famous ship Titanic was wrecked due to collision with a huge iceberg in its maiden voyage from Southamptom to New York City in 1912.
Short Explanatory Answer Type Questions
1. How many types of ocean currents are there? Describe them.
OR, What are warm and cold currents?
OR, What are surface currents and undercurrents?
Ans. Ocean currents are of two types-1. Warm currents and 2. Cold currents.
- Warm Currents: Ocean currents originating in the oceans of the torrid zone are warm and light. They flow through the upper part of the oceans, towards the cold polar regions. These are called the warm currents or the surface currents.
- Cold Currents: As the warm currents move towards the polar region, a temporary vacuum is created. Cold and heavy water from the polar regions flow towards the torrid zone deep under the sea. These are known as cold currents or undercurrents. Example-Labrador Current.
2. Why has a submerged bar been formed in Newfoundland of North America?
Ans. Newfoundland is located near the eastern coast of Canada. A number of submerged islands have been formed here, among which, the Grand Bank is the biggest.
Cause: The oppositely flowing cold Labrador Current (southward) and the warm Gulf Stream (northward) meet near Newfoundland. The icebergs coming down from the Arctic region with the cold Labrador Current melt here and the rocks, pebbles, clay and sands trapped within the icebergs get deposited. This goes on for ages and gradually some portion of ocean rise quite high underneath the waters as submerged bars.
3. How are ocean currents generated?
OR, What are the causes of formationof ocean currents?
OR, Why are ocean currents generated?
Ans. Ocean currents can be generated by various factors. Planetary winds moving across an expanse of water move the surface of the water and produce ocean currents. Warm areas of the ocean generate surface currents and from cold areas of the ocean undercurrents are generated. High salinity generates undercurrents and low salinity generates surface currents. The projected ends of the continents and the position of the coastline in the path of a current generate new ocean currents. The upward or downward changes of the bottom relief of the ocean generate currents. The earth’s rotation by deflecting moving ocean water generates ocean currents. Melting of ice changes the density of ocean water and helps to generate ocean currents.
4. Why is Newfoundland a famous fishing ground?
OR, Why is Grand Bank suitable for commercial fishing?
Ans. Newfoundland is situated on the eastern coast of Canada. Two oppositely moving ocean currents, the cold Labrador Current (southward) and the warm Gulf Stream (northward) meet in this area. Thus, icebergs melt and cause deposition of rocks, pebbles, clay and sand to form huge submerged bars. Grand Bank is such a submerged bar, famous for commercial fishing for the following reasons-
Causes:
- The Grand Bank is about 96,000 sq. km in area and the depth of the water is about 15-90m.
- The region lies in the temperate zone and have suitable climatic conditions (especially temperature) for the survival of fishes.
- The meeting of the cold and warm currents lead to growth of huge amount of planktons, which are the favourite food of the fishes.
- Various types of fishes like cod, herring, mackarel, haddock, halibut, etc., crowd here in huge numbers due to availability of planktons. Hence, commercial fishing can be done here.
5. Why are fishing grounds seen in the coastal areas of Japan?
Ans. Japan is situated in the North Pacific Ocean. The warm Kuroshio Current and the cold Kuril Current meet near the eastern coast of Japan. Thus, the icebergs carried with the cold Kuril or Kamchatka Current melt as they come in contact with the warm Kuroshio Current. The rocks, pebbles, clay, sand particles, etc., entrapped in icebergs get deposited near the coast on the continental shelf and form submerged bars. Here sunlight can reach the bottom of the seafloor and favour growth of planktons, which is a favourite food of the fishes. Thus, various kinds of fishes crowd in this region and help in the development of fishing grounds.
6. Why is dense fog seen in the eastern coast of Japan?
Ans. In the oceans, wherever the warm currents and cold currents meet, the water vapour present in the warm air over the warm current come in contact with the cool air over the cold current. Thus, the water vapour condenses into tiny droplets of water which remain suspended in the air and form dense fog. In Japan, the warm Japan Current or Kuroshio Current moves northward, while the cold Kuril or Oyashio Current moves southward along the eastern coast. Thus, the meeting of these two warm and cold currents form dense fog near the eastern coast of Japan.
7. Why does the coastal region of Newfoundland remain foggy throughout the year?
Ans. In the oceans, where the warm currents and cold currents meet, the water vapour, present in the warm air over the warm current comes in contact with the cool air over the cold current. Thus, the water vapour condenses into tiny droplets of water which remain suspended in the air and form dense fog. Along the coast of Newfoundland, the warm Gulf Stream moves towards the north and the cold Labrador Current moves towards the south. The meeting of these two opposite currents create dense foggy conditions throughout the year.
8. Describe the ocean currents flowing through the northern part of Indian Ocean during summer.
Ans. The Indian Ocean has two oppositely moving ocean currents in the summer and winter seasons. The branch of the South Equatorial current that enters the Indian Ocean follows the direction of the monsoon winds, and hence is known as the monsoon current. During summer, under the influence of the south-west monsoon winds, the current moves towards the right along the eastern coast of Africa. It flows as the Somali Current in the north-eastern direction. Later, the current flows through the Arabian Sea and Bay of Bengal as the South-west Monsoon Current upto Sumatra.
9. What is ‘hydrosphere’?
Ans. About 71% of the earth’s surface is covered with water. Water bodies like lakes, ponds, rivers, oceans, gulfs, etc., make up the total water contained on the earth. This is known as the hydrosphere. The oceans are the largest water bodies on the earth. Ocean water flows from one region to another through ocean currents. This controls the climate of the region to a great extent.
10. How are the ocean currents named?
Ans. Ocean currents are named according to the regions they cross and the seas or gulfs they flow through. For example- the Caribbean Current is so named as it flows through the Caribbean sea; the Brazil Current is so named as it passes along the coast of Brazil.
11. Why is the climate of New York colder than that of London, inspite of New York lying at a lower latitude than London?
Ans. London lies at 51°30′26″N latitude and New York lies at 40°43’N latitude. Under normal conditions London should have a colder climate than New York, as it lies at a higher latitude than New York. However it is seen that the climate of New York is colder than that of London. This is because of the influence of ocean currents. The cold Labrador Current passes near New York and makes the climate cold. On the other hand, the warm North Atlantic current flowing west of London makes the climate of the city warm.
12. How do ocean currents cause changes in climatic conditions?
Ans. Ocean currents cause changes in climatic conditions by the following ways-
- Control on temperature: The warm currents move towards the polar regions from the equatorial region, and the cold currents flow towards the equatorial region from the polar region. This helps in maintaining a balance between the temperatures of various places, due to exchange of heat.
- Rainfall and snowfall: The regions along which warm currents flow experience heavy rainfall. The regions along which cold currents flow are more prone to snowfall than rainfall.
- El Nino and La Nina: During El Nino, a warm current flows from the north towards the coast of Peru and Ecuador in South America. This causes heavy rainfall in those regions. However, chances of droughts increase in India and Australia. During La Nina, opposite climatic conditions prevail. Australia experiences heavy rainfall, India experiences moderate rainfall and Peru and Ecuador experience droughts.
Short Answer Type Questions
1. How many oceans are there in the world? Name them.
Ans. There are five oceans in the world. They are-1. Pacific Ocean, 2. Atlantic Ocean, 3. Indian Ocean, 4. Arctic Ocean and 5. Antarctic Ocean.
2. What is the Gulf Stream?
Ans. In the Atlantic Ocean, the northern branch of the South Equatorial Current (warm current) and the North Equatorial Current (warm current) meet together and move westwards towards the Gulf of Mexico under the influence of the trade winds. This current is known as the Gulf Current or the Gulf Stream.
Characteristics
- This is a warm current.
- The Gulf Stream appears blue in colour.
- The average temperature is about 27°C.
- The ocean current is 800-1200 m deep, 100 km wide and 65 km long. It moves at a maximum speed of 9 km/hr.
3. What is Sargasso Sea?
OR, How is Sargasso Sea formed?
Ans. In the north Atlantic Ocean, a large portion of the water is encircled by the Gulf Stream in the west, North Atlantic Current in the north, Canary current in the east and North Equatorial
current in the south. This region is absolutely calm with no currents and flow. The water is stagnant and a huge amount of sea weeds, mosses and other aquatic plants grow here. Thus, this region is called the Sargasso Sea.
4. What is an ocean current?
Ans. The stream of water that flows from one place to another, regularly within the ocean itself, is called an ocean current. Ocean currents are of two types-warm currents and cold currents.
5. What do you mean by the ‘cold wall’?
Ans. In North America, along the eastern coast, the warm Gulf Stream flows towards the north and the cold Labrador Current flows towards the south side by side. The division between the blue waters of the Gulf Stream and the green waters of the Labrador Current can be seen from far away for a long distance. This is known as the ‘cold wall’. This is not related to the height of the water column at the meeting point of these two ocean currents.
6. How are submerged sandbars created?
Ans. At places where the warm and cold currents meet, the icebergs coming with the cold currents melt as they come in contact with the warm currents. Thus, the rocks, pebble, sand and clay present in the icebergs get deposited on the continental shelf of the oceans. With regular depositions, the height of the shallow ocean floor start rising gradually. When it reaches such a height that it appears like a landform submerged a little below the sea level, it is called a submerged sandbar or submerged bar. Example-Grand Bank near the coast of Newfoundland, Dogger’s Bank near the British Isles.
7. Which ocean current is known as the Labrador current?
Ans. The Labrador current is a cold current flowing through the North Atlantic Ocean. It originates from the Arctic Ocean and flows southwards between Greenland and Canada (i.e., western coast of Greenland) and passes around Newfoundland and moves further southwards. This ocean current is a continuation of the West Greenland Current and the Baffin Island Current.
8. Which ocean current is known as the Brazil current?
Ans. In the Atlantic Ocean, the South Equatorial Current moves westwards and gets obstructed by the cape of St. Roch in Brazil. Here the current bifurcates into two branches, and the southern branch is known as the Brazil current.
9. Which is the Peru or Humboldt Current?
Ans. The Peru or Humboldt Current flows through the Southern Pacific Ocean. This cold current originating under the influence of the westerly winds moves eastwards and gets obstructed by the western coast of South America. Then, it moves northwards along the coast of Peru after crossing Chile.
10. Which is the Japan or Kuroshio Current?
Ans. The Japan current or the Kuroshio current is an important warm current flowing through the North Pacific Ocean. The west flowing North Equatorial Current originates in the Pacific Ocean under the influence of the South-east trade winds. This current moves northwards along the eastern coast of Japan, where it is known as the Japan current or the Kuroshio current.
11. Which is the Benguela Current?
Ans. The Benguela Current is a cold current flowing through the Atlantic Ocean. In the Antarctic Ocean, the cold Antarctic Current originates, which move eastwards under the influence of the westerlies. This current gets obstructed by the south-western coast of Africa and moves northwards parallel to the western coast of Africa. Here, it is known as the Benguela Current.
12. What do you mean by the monsoon current?
Ans. Monsoon currents are ocean currents generated in the northern part of the Indian Ocean due to the influence of the monsoon winds. These currents flow in opposite directions during summer and winter seasons. During summer, the current flows under the influence of the South-west monsoon winds. It moves in a circular path from the right side along the eastern coast of Africa through the Arabian Sea and Bay of Bengal and flows upto the island of Sumatra. During winter, the current flows under the influence of the North-east monsoon winds. It moves in the opposite direction, i.e., in a circular motion from the leftside.
13. What are icebergs?
Ans. The small and large floating hills of ice found in the oceans are called icebergs. Only 1/9th part of an iceberg remains above the ocean surface and the rest remains submerged in water.
The famous ship called ‘Titanic’ sunk after colliding with a huge iceberg in its maiden voyage.
14. What do you mean by gyre?
Ans. If the movement of ocean currents in all the oceans is carefully looked at, a common pattern emerges. The water, in all the oceans have a circular motion. This is known as gyre. ‘Gyre’ is of two types-1. Sub-tropical gyre and 2. Sub-polar gyre. In both the hemispheres between 25°-30° latitudes, the trade winds and the westerlies influence the ocean water to move around the sub- tropical high pressure belt in a circular path.
15. What are undercurrents?
Ans. The cold, dense and heavy water from the polar regions gradually flow towards the lower latitudes or the torrid zone. The water moves through the deeper layers of the sea. These are called undercurrents.
16. What are surface currents?
Ans. The ocean currents generated in the torrid region or the warm region of the earth are warm, less dense and light. Thus, they flow in the upper part i.e., near the ocean surface. These are called surface currents.
17. Why are fish found in huge quantities near the coast of Japan?
Ans. The cold Kamchatka or Oyashio Current and the warm Kuroshio Current meet near the eastern coast of Japan. The icebergs brought in by the cold current melt after coming in contact with the warm current. Thus, the gradual deposition of rocks, pebbles, clay and sand particles create submerged sandbars. These submerged bars are ideal places for the growth of planktons, the nutrient-rich food of the fish. Hence, huge quantity of fish are found near the eastern coast of Japan.
Multiple Choice Type Questions [MCQ type]
Write the correct answer from the given alternatives
1. Cold wall is seen in-
A. Atlantic Ocean
B. Antarctic Ocean
C. Indian Ocean
D. Pacific Ocean
Ans. A
2. Which of the following currents flows along the eastern coast of Madagascar?
A. Somali
B. Madagascar
C. Agulhas
D. South-west monsoon
Ans. B
3. Which of the following is a warm current?
A. Kamchatka
B. Peru
C. Brazil
D. West Australian
Ans. C
4. Ocean currents are generated due to the-
A. Difference in temperature
B. Difference in salinity
C. Movement of planetary winds
D. All the above are correct
Ans. C
5. The ocean current flowing along the south-western coast of South America towards the north is-
A. Falkland current
B. Humboldt current
C. New South Wales current
D. California current
Ans. B
6. The speed of ocean currents in shallow seas compared to deep seas is-
A. More
B. Less
C. Not affected
D. Remains same
Ans. A
7. Which of the following is a warm current flowing through the Gulf of Mexico?
A. North Equator current
B. North Atlantic current
C. Gulf stream
D. South-west monsoon current
Ans. C
8. The Peru current flows through the-
A. Indian Ocean
B. Atlantic Ocean
C. Pacific Ocean
D. Arctic Ocean
Ans. C
9. Grand Bank is a-
A. Warm current
B. Cold current
C. Submerged bar
D. Island
Ans. C
10. Sargasso Sea is seen in the-
A. Atlantic Ocean
B. Indian Ocean
C. Antarctic Ocean
D. Arctic Ocean
Ans. A
11. The current which flows along the western coast of Madagascar is-
A. Somali current
B. Madagascar current
C. Mozambique current
D. Agulhas current
Ans. C
12. The largest and deepest ocean is the-
A. Pacific Ocean
B. Atlantic Ocean
C. Indian Ocean
D. Arctic Ocean
Ans. A
13. In which ocean has the Sargasso Sea formed by four currents forming an ocean gyre?
A. Pacific Ocean
B. Atlantic Ocean
C. Indian Ocean
D. Antarctic Ocean
Ans. B
14. Dense fog occurs near Newfoundland due to-
A. Meeting of Canary current and Gulf stream
B. Meeting of Gulf stream and Labrador current
C. Meeting of Gulf stream and Equatorial current
D. Meeting of Gulf stream and North Atlantic current
Ans. B
15. A floating chunk of ice is called-
A. Ice wall
B. Snow line
C. Iceberg
D. Snow field
Ans. C
16. The eastern coast of Japan remains warm even in winter due to the-
A. Bering current
B. Gulf stream
C. Kuroshio current
D. North-east monsoon current
Ans. C
17. The monsoon winds control the-
A. Pacific Ocean currents
B. Indian Ocean currents
C. Atlantic Ocean currents
D. Arctic Ocean currents
Ans. B
18. The largest number of ships sail on the-
A. South Indian Ocean
B. North Pacific Ocean
C. South Atlantic Ocean
D. North Atlantic Ocean
Ans. D
19. Ocean currents are created by-
A. Rotation of the earth
B. Revolution of the earth
C. Gravitational force
D. None of these
Ans. A
20. The maximum speed of Gulf stream is-
A. 5 km/hr
B. 9 km/hr
C. 15 km/hr
D. 20 km/hr
Ans. B
21. The Gulf stream appears-
A. Deep green
B. Deep red
C. Deep blue
D. Light violet
Ans. C
22. Tidal bores are seen in-
A. River Yamuna
B. River Ichamati
C. River Hooghly
D. River Ajay
Ans. C
23. The ocean currents of the northern Indian Ocean are controlled by the-
A. Trade winds
B. Planetary winds
C. Local winds
D. Monsoon winds
Ans. D
24. The California current flows through the ……….. Ocean.
A. Atlantic
B. Indian
C. Pacific
D. Arctic
Ans. C
25. Area of total surface covered by water on the Earth’s surface is nearly-
A. 61%
B. 81%
C. 71%
D. 91%
Ans. C
26. The merging of cold Labrador Current and warm Gulf Stream Current create dense fogs and stormy weather conditions along-
A. Newfoundland Coast
B. Guinea Coast
C. Florida Coast
D. Peru Coast
Ans. A
Very Short Answer Type Questions
Fill in the blanks with suitable words
1. The warm ………. current keeps the east coast of Japan warm in winters.
Ans. Kuroshio
2. ……… is the largest ocean of the world.
Ans. Pacific Ocean
3. ……… is created at the meeting points of warm and cold currents.
Ans. Fog
4. ………. forms where the warm Gulf stream and the cold Labrador current meet.
Ans. Cold wall
5. The cold ……… current flows through the Arctic Ocean towards the coast of Japan.
Ans. Kamchatka
6. The cold ……… current flows along the eastern coast of South America towards the north.
Ans. Falkland
7. Waves are ……….. movement of water on the surface of the oceans.
Ans. Up and down
8. The water in oceans always move from the equatorial region towards the ……….
Ans. Poles
9. ………. percent of the earth’s surface is occupied by oceans.
Ans. 71
10. The presence of water on the earth’s surface gives it the name ………..
Ans. Blue planet
11. Heavy saline water flows as ………..
Ans. Undercurrent
12. The average speed of ocean currents is ……….
Ans. 5-10 km/hr
Answer in one or two words
1. What is the movement of ocean water from one place to another called?
Ans. Ocean currents.
2. What is the upward and downward movement of ocean water called?
Ans. Ocean waves.
3. What are the waves splashing on the coast of oceans called?
Ans. Swash.
4. What are the waves retreating from the coastline into the ocean water called?
Ans. Backwash.
5. What are the backwash waves also known as?
Ans. Destructive waves.
6. What are the small waves that help to form the coast called?
Ans. Constructive waves.
7. What are the ocean currents flowing through the outer part of the oceans called?
Ans. Surface currents.
8. What are the ocean currents flowing through the interior or deep layers of the oceans called?
Ans. Undercurrents.
9. Which is the main controlling factor of ocean currents?
Ans. Planetary winds.
10. In which direction do the warm currents flow?
Ans. From the equator towards the poles.
11. In which direction do the cold currents flow?
Ans. From the poles towards the equator.
12. Name a submerged bar in the Atlantic Ocean.
Ans. Grand Bank.
13. Which hemisphere has the maximum volume of water bodies?
Ans. Southern hemisphere.
14. Name the deepest ocean of the world.
Ans. Pacific Ocean.
15. Which winds control the ocean currents of the northern part of Indian Ocean?
Ans. South-west and north-east monsoon winds.
16. The currents of which ocean are influenced by the monsoon winds?
Ans. Indian Ocean.
17. In which ocean Sargasso Sea is seen?
Ans. Atlantic Ocean.
18. Name the deepest ocean trench of the world.
Ans. Mariana trench.
19. What is the stagnant water within an ocean, where sea weeds grow called?
Ans. Sargasso Sea.
20. Which two currents combine to form the Agulhas current?
Ans. Mozambique current and Madagascar current.
21. Name an ocean current of the Atlantic Ocean.
Ans. Benguela current.
22. What is the main food of marine fish?
Ans. Plankton.
TOPIC – 2
Tides
Long Answer Type Questions
1. Explain the reasons or causes of tides.
OR, How are tides formed?
Ans. The swelling and falling of the ocean waters at regular intervals is known as tides. The tides are formed due to the following factors-
- Attraction of the moon and the sun: According to the theory of Newton, each and every matter in the universe that has mass, attract each other. Hence, there is an attraction between the sun, moon and the earth. The attraction of the moon is greater than the attraction of the sun on the earth. This is because, although the sun is about 2 crore 70 lakh times larger than the moon, it is about 400 times farther away from the earth than the moon. Thus, the attraction of the moon in forming tides is much more effective than the attraction of the sun. The sun also helps to form tides, but the tides formed by the moon is much more intense. But, it should be noted that, when the sun, moon and earth lie approximately in a straight line, the tides formed are the most intense. The tide formed on the side facing the moon is known as the primary tide. The tide formed on the opposite face of the primary or direct tide is known as the secondary or indirect tide. While the tides are high in these two locations, the water level at the locations perpendicular to them, falls. Hence, these locations experience ebb tides or low tides.
- Centrifugal force developed due to rotation of the earth: The earth is rotating on its axis continuously. This creates a centrifugal force, which tends to throw out the moving bodies like air and water from the surface of the earth. This force acts in the direction opposite to the force of gravity. Thus water seems to rise at places due to the centrifugal force.
2. How are spring tides and neap tides caused?
OR, Discuss the formation of spring tides and neap tides.
OR, What do you mean by spring tides? How do they occur?
OR, Why do spring tides always occur on new moon and full moon days?
Ans. Spring tides: During the full moon, the earth lies in between the sun and the moon in a straight line. During the new moon, the moon lies in a straight line between the sun and the earth. On these two days, due to the combined attraction of the sun and the moon (especially on the new moon day), the water level rises to the maximum height possible. This is known as the spring tide.
- New moon: The moon and the sun lie on the same side of the earth in a straight line on a new moon day. Thus, the attraction powers of the sun and the moon combine together and pull the water of the oceans from the same side. Hence, the tide occurring on the side facing the moon is the maximum compared to the tide on the opposite side.
- Full moon: The earth lies in between the sun and the moon in a straight line on a full moon day. The sun and the moon lying on either side of the earth pull the water of the oceans from both the sides. This creates high tides on either sides, but the intensity is not as high as that on new moon day.
Neap tides: During the first and third quarters of the moon, the sun and the moon lie at right angles to each other with respect to the earth. The power of attraction of the sun and the moon work at right angles to each other, and hence cancel each other. Thus, the difference in level of water during high tides and low tides is not much. This is known as neap tide.
Short Explanatory Answer Type Questions
1. How are the tides caused?
Ans. The water in the oceans and seas rise and fall alternately at regular intervals. This up and down movement of the level of ocean water is known as tides.
Causes: The main causes of tides are- 1. Attraction of the sun and the moon. 2. Centrifugal force generated by the rotation of the earth.
Since, the moon lies much closer to the earth compared to the sun, the attraction of the moon is much more effective in forming tides compared to the sun.
During rotation, when a side of the earth faces the moon, the water level of that side rises due to attraction of the moon. At the same time, the antipode of the place also experiences rise in ocean water level due to centrifugal force of the earth. Thus, a primary or direct tide is generated at the first place, and an indirect or secondary tide is generated at its antipode.
The places lying at right angles of these two places experience low tides at that time. Increase of water level due to attraction of the moon and the centrifugal force draw away a huge quantity of water from the places lying at right angles. Thus, low tides or ebb tides are caused.
2. Mention the effects of tides.
OR, What are the effects of tides on human life?
OR, Discuss the advantages and disadvantages of tides.
Ans. The effects of tides on human life are discussed below:
- Advantages of tides: (1) Large ships can sail into the rivers during high tides, and sail out during low tides. (2) Tides help to remove the silt and other depositions of the river into the sea, and keep the river channel deep and navigable. (3) Tides can be used to produce tidal energy. (4) Tides help in development of fishing activities as a huge amount of fishes enter the rivers from the oceans during tides. (5) The saline water of the oceans that enter the ports and rivers during high tides help to keep the ports and river mouths ice-free during winters.
- Disadvantages of tides: (1) Tides make the river water saline which makes it unsuitable for agriculture, industrial activities or drinking. (2) The rise of water level during strong high tides often inundate agricultural fields and damage houses built near river banks. (3) Tides may damage water vessels like boats, launches, small ships, etc. (4) Tides sometimes may lead to additional deposition of silt and other materials in the rivers brought in along with the ocean waters. This reduces the depth of the river channels.
3. Why are the spring tides known as the highest tides?
Ans. Spring tides occur on new moon and full moon days. During new moon, the earth, sun and moon lie approxmimately in a straight line, and the moon lies in between the earth and the sun. During full moon, the earth comes in between the sun and the moon when all three lie approximately in the straight line. Compared to other days, the level of water during high tide rises much higher on the new moon and full moon days due to double attraction of the sun as well as the moon. Thus, the spring tides are also known as the highest tides.
4. What is the interval of time between a high tide and a low tide?
OR, Why does high tide and low tide not occur at the same time at the same place everyday?
OR, Why is the interval between primary and secondary tides of a place 12 hours 26 minutes apart?
OR, Why do high tides and low tides occur twice at a place in one day?
OR, Why is the time interval between two primary tides more than 24 hours?
OR, Why is the time interval between two primary tides of a place 24 hours 52 minutes?
Ans. The moon takes about 27 1/3days to complete one revolution around the earth. When the earth completes one rotation around
its axis in 24 hours, the moon moves 1/27th part of its orbit, i.e. [360° +27 = 13] 13°. The earth takes more [4 x 13° = 52 min] 52 minutes to cover this distance. Hence, a particular place on the earth surface faces the moon once again after 24
hours 52 minutes. Thus, primary tide occurs at the same place after 24 hours 52 minutes. Secondary tide occurs after 12 hours 26 minutes at the place which experiences primary tide. The places lying at right angles to the places experiencing high tides experience low tides. Thus, time interval between a high tide and a low tide is 6 hours 13 minutes.
5. What are tidal bores?
OR, Write a short note on tidal bores.
Ans. During high tides, when the level of water in the oceans rises, the excess water flows into the rivers through the river mouth. This increases the level of water in the rivers as well. If the water enters with great speed and raises the water level by 5-7m, it is known as a tidal bore.
Favourable conditions for the occurence of tidal bores are as follows-
1. During spring tides, 2. If there are sandbars at the mouth of rivers, 3. If the water is obstructed somehow while entering the river during high tides. 4. If the shape of the mouth of the river is like a funnel. 5. If the river is already filled with water till the banks.
6. What are primary and secondary tides?
OR, How are primary and secondary tides caused?
Ans. Primary tide: Tides are caused due to the attraction of the moon and the sun and the centrifugal force developed due to the rotation of the earth. But, among these, the attraction of the moon is considered as the main cause of formation of tides. During rotation, the side of the earth that faces the moon, experiences maximum rise in the water level during high tide due to maximum attraction of the moon. This is known as the primary or direct tide.
Secondary tide: During a primary tide, the place lying at the antipode of the first place also experiences a high tide due to the centrifugal force of the earth. However this tide is not as high as the primary tide. This is thus known as the secondary or indirect tide.
7. What are spring tides and neap tides?
Ans. Spring tides: During the new moon and full moon, the sun, earth and moon lie approximately in a straight line. Thus, the water level rises very high during high tides due to the combined attraction of the sun and the moon. These tides are known as spring tides.
Neap tides: During the first and third quarters of the moon, the sun and the moon lie approximately at right angles with respect to the earth. Thus, the attractions of the sun and the moon are countered by each other. This leads to very low rise in water levels during the high tides. These tides are known as neap tides.
8. Why is the primary tide caused on a new moon night more intense than the primary tide caused on a full moon night?
Ans. During the full moon, the earth, sun and moon lie in a straight line and the earth lies in between the sun and the moon. The place of the earth that faces the moon, experiences primary tide due to more attraction of the moon and less attraction of the sun. On the other hand, during the new moon, while the earth, moon and sun lie approximately in a straight line, the moon lies in between the earth and the sun. Now when a place of the earth faces the moon, it experiences very high and intense tide due to combined attraction of the moon and the sun from the same direction. Thus, the intensity of primary tides on new moon nights is much more compared to that on full moon nights.
9. Why is the swelling of water during a neap tide much less compared to the swelling of water during the spring tide?
Ans. During full moon and new moon, the sun, moon and the earth lie approximately in a straight line, and the spring tides are caused by the combined attraction of the sun and the moon. But during the first and third quarters of the moon, the sun and the moon lie approximately at right angles with respect to the earth. They counter or oppose each other’s force of attraction. Hence, the tides caused at the places facing the moon are less intense and swelling of water is less. These are known as neap tides, when the swelling of water is much less compared to the swelling of water during the spring tides.
10. Why do tidal bores occur in the river Ganga?
Ans. The rushing in of water from the ocean into the river through the river mouth at great speed is known as tidal bore. The level of water in the river may rise upto 5-7 m during a tidal bore. The tidal bores in the river Ganga are caused due to the following reasons-
- The mouth of the river Ganga is like a funnel, i.e., the mouth is quite wide and open, but the river channel is comparatively narrow.
- There are number of sandbars present near the mouth of the river Ganga.
- The river already remains filled with water during the rainy season.
- The water from the Bay of Bengal is obstructed by the river currents while entering the river channel.
11. How do the tides influence the navigability of the rivers?
Ans. The tides influence the navigability of rivers in the following ways-
- Tides help to remove the silt and other materials from the river channels and increase the depth of the channels. This makes the rivers better navigable.
- The water level of rivers increase during high tides, and helps large ships to enter the rivers. The ships can leave the rivers and sail back to the ocean during low tides.
- Low tides help to remove silt and other materials from the river mouths and increase the depth of the channels.
Short Answer Type Questions
1. What do you mean by tides?
Ans. The height of the ocean waters rises in some places and falls in other places alternately throughout the year. This is known as tides. Tides occur mainly due to the attraction of the moon, attraction of the sun and centrifugal force generated due to rotation of the earth. Tides can be classified as-high tides and low tides.
2. What are tidal bores?
Ans. During the rainy season, when a spring tide occurs, water suddenly rushes back into the river channel due to rise in the level of water in the ocean. This is known as a tidal bore. During tidal bores, the water may rise upto 6-8m and flow with great speed in the opposite direction of the flow of the rivers. The water flows with a roaring sound during the tidal bores.
3. Mention the two main causes of tides.
Ans. The main causes of tides are-
1. Gravitational pull of the moon and the sun. 2. Centrifugal force generated due to rotation of the earth.
4. What do you mean by conjunction and opposition?
Ans. Conjunction: The position where the earth, moon and sun lie approximately in a straight line with the moon lying in between, is known as conjunction. This occurs on new moon days.
Opposition: The position where the earth, moon and sun lie in a straight line, with the earth lying in between, is known as opposition. This occurs on full moon days.
5. What is ‘syzygy’?
Ans. The position where the earth, moon and the sun lie approximately in a straight line is called ‘syzygy’. It can be classified into two types-
1. Conjuction: When the moon lies in between the sun and the earth.
2. Opposition: When the earth lies in between the sun and the moon.
Effects: Syzygy causes very powerful tides. Thus spring tides occur on full moon or new moon nights.
6. What are lunar tides?
Ans. During the rotation of the earth, the side of the earth that comes in front of the moon faces its maximum gravitational pull. Thus, water in this region rises the maximum during high tides. These tides are known as lunar tides.
7. What are solar tides?
Ans. The swelling of water that occurs due to the attraction of the sun, is known as the solar tide. The attraction of the sun is much lesser than the moon due to greater distance between the sun and the earth. Thus, the intensity of the solar tides is also less.
8. What are spring tides?
Ans. During the new moon and full moon, the sun, moon and the earth lie on the same straight line. This is known as syzygy. The tides formed during this time are called spring tides. Water rises maximum during these tides.
9. What are neap tides?
Ans. During the first or third quarter of the moon, the sun and moon lie perpendicular to each other with respect to the earth. The places on earth which face the moon and sun experience high tides. But, as the sun and the moon lie perpendicular to each other, both try to pull the water towards it. Thus, the tides do not become intense. These are known as neap tides.
10. Why are spring tides also known as the highest tides?
Ans. On new moon and full moon days, the sun, moon and the earth lie in the same straight line. Especially, during new moon, the moon comes in between the earth and the sun. The tides formed due to the combined attraction of the sun and the moon are the highest. Hence, such tides are known as highest tides.
11. What is the direction of flow of water in tides?
Ans. The water in tides rises and falls in a particular direction due to the rotation of the earth. Thus, water moves from east to west during high tides, and moves in the direction from west to east during ebb tides.
Multiple Choice Type Questions [MCQ type]
Write the correct answer from the given alternatives
1. Tides can be seen in river-
A. Tista
B. Sutlej
C. Yamuna
D. Hooghly
Ans. D
2. Saline water is-
A. Light
B. Heavy
C. Warm
D. Cold
Ans. B
3. The part of the earth that faces the moon, experiences-
A. Spring tide
B. Neap tide
C. Primary tide
C. Ebb tide
Ans. A
4. High tides occur ………. in every 24 hours 52 minutes.
A. Once
B. Twice
C. Thrice
D. Four times
Ans. B
5. Neap tide occurs on-
A. Full moon
B. New moon
C. First and third quarters of the moon
D. Second day after full moon
Ans. C
6. Neap tides occur when the moon lies ……. to the sun.
A. Perpendicular
B. Parallel
C. On the same line
D. Opposite
Ans. A
7. The time interval between two high tides is-
A. 6 hr 13 min
B. 12 hr 26 min
C. 24 hr 52 min
D. 24 hr 55 min
Ans. C
8. The moon revolves around the earth once in about-
A. 27 days
B. 29 days
C. 30 days
D. 28 days
Ans. A
9. During new moon, the side of the earth that faces the moon during day time experiences-
A. Spring tide
B. Neap tide
C. Ebb tide
D. None of these
Ans. A
10. The mass of the sun compared to the moon is about-
A. 25 million times greater
B. 27 million times greater
C. 52 million times lesser
D. 15 million times greater
Ans. B
11. The attraction power of the moon over the earth compared to the sun is-
A. 1.1 times greater
B. 2.2 times greater
C. 3.3 times lesser
D. 5.5 times greater
Ans. B
12. The centrifugal force causes-
A. Secondary tides
B. Primary tides
C. Spring tides
D. Neap tides
Ans. A
13. The antipode of the place facing high tides experience-
A. Secondary tides
B. Neap tides
C. Solar tides
D. Ebb tides
Ans. A
14. The position of the sun, moon and the earth on the same straight line is known as-
A. Apogee
B. Perigee
C. Syzygy
D. Aphelion
Ans. C
15. The sun is ……… times heavier than the moon.
A. 270 lakh
B. 200 lakh
C. 25 lakh
D. 10 lakh
Ans. A
16. The distance between the earth and the moon at perigee position is-
A. 3 lakh 84 thousand km
B. 3 lakh 63 thousand km
C. 4 lakh 57 thousand km
D. 3 lakh 76 thousand km
Ans. B
17. The upswelling of water during tides at Perigee compared to other positions is …….. greater.
A. 10%
B. 20%
C. 30%
D. 40%
Ans. B
18. Conjunction occurs during-
A. Full moon
B. New moon
C. 7th day after full moon
D. 8th day after new moon
Ans. B
19. Duration of both high tide and low tide is nearly-
A. 2 hours
B. 6 hours
C. 4 hours
D. 8 hours
Ans. B
20. On the days of Neap Tides the sun and the moon are at the following angles to each other in respect of the earth-
A. 180°
B. 360°
C. 90°
D. 120°
Ans. C
Very Short Answer Type Questions
Fill in the blanks with suitable words
1. ……… tides occur in the direction towards which the rivers flow.
Ans. Ebb
2. ……… occurs due to rotation and centrifugal force of the earth.
Ans. Secondary tides
3. Spring tides occur in a place every ………. days.
Ans. 15
4. When the water rises during high tides and rushes into the rivers in opposite direction, it is called ………
Ans. Tidal bore
5. The distance between the earth and the sun is ………. times greater than distance between the earth and the moon.
Ans. 391
6. Secondary tides occur due to the ………. force.
Ans. Centrifugal
7. Primary tides occur due to the attraction of the ……….
Ans. Moon
8. The fishes enter the rivers from the ocean during ……….
Ans. High tides
9. ‘Kadal’ means ……….
Ans. Ocean
10. Neap tides occur on the ……… of the moon.
Ans. First and third quarters
11. The syzygy position during new moon is known as …………
Ans. Conjunction
12. Tides are used to produce ……….. energy.
Ans. Tidal
13. High tides and low tides occur ………. daily.
Ans. Twice
14. Tidal bores occur frequently in ………. season.
Ans. Monsoon
15. Tidal bores occur in a river during ………..
Ans. High tides
16. The tides occuring due to the moon’s attraction are called ………
Ans. Lunar tides
17. The moon traverses …….. in one day on its orbit.
Ans. 13°
18. Tides swell maximum during the ………..
Ans. New moon
19. The small sea waves that help to form the coast are called ………. waves.
Ans. Constructive
20. The open part of the sea is called ………..
Ans. Fetch
21. The ……… waves damage the sea coast.
Ans. Destructive
22. During high tide huge tidal waves entering through the mouth of a river from the sea are called as ……….
Ans. Tidal Bore
Answer in one or two words
1. What percentage of the earth’s surface is covered with water?
Ans. 71%.
2. How much area of the earth’s surface is covered with water?
Ans. 36 crores, 17 lakh, 40 thousand sq. km.
3. What is the earth also known as due to presence of 71% of water on its surface?
Ans. Blue planet.
4. What is the average distance between the moon and the earth?
Ans. 384,000 km.
5. What is the main cause of tides?
Ans. The attraction of the moon and the sun.
6. What are tides formed due to attraction of the moon called?
Ans. Lunar tides.
7. What are tides formed due to gravitational attraction of the sun called?
Ans. Solar tides.
8. How many times does high tides occur in a region in a day?
Ans. Twice.
9. What is the interval between two secondary tides?
Ans. 12 hrs 26 mins.
10. What is the interval between two consecutive primary tides?
Ans. 24 hrs 52 mins.
11. Which seas do not experience tides?
Ans. Mediterranean sea, and Baltic sea.
12. How much angle does the moon traverse in one day?
Ans. About 13°.
13. What is the position of the earth, sun and the moon lying in a straight line called?
Ans. Syzygy.
14. Name a river which is prone to the actions of the tidal bores.
Ans. River Hooghly.
15. Which energy causes secondary waves?
Ans. The gravitational attraction of the sun.
16. When do tidal bores occur?
Ans. During spring side.
17. According to relative location, what is the physical location between the moon and the earth?
Ans. 4 lakh 05 thousand km. (According to NASA)
18. Which tides are accompanied by tidal bores generated in the oceans?
Ans. Primary tides.
19. What is the distance between moon and the earth during perigee?
Ans. 3 lakh 60 thousand km. (According to NASA)
20. What is the ratio of the moon and sun’s capacity to cause tides?
Ans. 11:5.
21. What is the shape of the earth’s orbit?
Ans. Elliptical.
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