Selina Concise Solutions for ICSE Class 9 Geography Chapter 11 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.
Ocean water is constantly moving due to the planet spinning and the wind blowing across the surface. Differences in salt levels also act like a pump, moving water from one area to another to balance the ocean.
Teacher's Tip: Use the acronym "RWS" to remember the causes: Rotation, Winds, and Salinity.
Exam Tip: Mentioning "Rotation of the Earth" as the first factor is essential for a complete answer.

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.
Tides are like the ocean "breathing" in and out at regular times during the day. They happen because the Moon and Sun act like giant magnets pulling the Earth's water toward them.
Teacher's Tip: Think of the Moon as a giant "Water Magnet" in space that tugs at our oceans.
Exam Tip: Always state that both the Sun and the Moon cause tides, but the Moon's effect is stronger because it is closer to Earth.

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.
Because the Moon is moving while the Earth is spinning, it takes a little bit longer for a specific spot on Earth to face the Moon again. This "catch-up" time is why the tide happens about 50 minutes later each day.
Teacher's Tip: Remember the number 52; it is the total daily delay in minutes for the tide to return to the same spot.
Exam Tip: To get full marks, you must mention both the "24 hours 52 minutes" cycle and the "12 hours 26 minutes" interval between consecutive high tides.

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.
Spring tides are the strongest tides because the Sun and Moon pull together in a straight line. Neap tides are the weakest because the Sun and Moon pull in different directions, forming an "L" shape.
Teacher's Tip: "Spring" tides "spring up" high, while "Neap" tides are "nipped" or smaller.
Exam Tip: Use the term "right angle" to describe the position of the Sun and Moon during a Neap tide.

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.
Ocean currents are like giant rivers of water in the sea that are either warm or cold. Warm currents bring heat to cold places, while cold currents bring cool water toward the equator.
Teacher's Tip: Think of the Gulf Stream as a "warm blanket" for Europe and the Labrador Current as an "ice pack" for North America.
Exam Tip: Providing a specific example like the "Gulf Stream" for warm currents will help you score full marks.

Question 6: For what is the Gulf Stream famous?
Answer:
The Gulf Stream acts like a giant heater for Western Europe, making places like the UK much warmer than they would be otherwise. Because it moves so much water so quickly, scientists are also looking at ways to capture its power for electricity.
Teacher's Tip: Think of the Gulf Stream as the "Central Heating System" of the Atlantic Ocean.
Exam Tip: Mention that it flows along the eastern coast of North America to describe its location accurately.

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.
When these currents clash, the difference in temperature creates thick mist and fog, making it dangerous for ships to navigate. However, these areas are perfect for tiny sea plants to grow, which attracts millions of fish, making them the best fishing spots on Earth.
Teacher's Tip: Think of a hot shower in a cold bathroom; the "steam" or fog you see is exactly what happens in the ocean!
Exam Tip: Always link the meeting of currents to two things: "Dense Fog" and "Rich Fishing 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%.
Salinity tells us how "salty" the water is, usually measured by how many grams of salt are found in 1,000 grams of water. On average, if you evaporated a bucket of seawater, about 3.5% of what is left behind would be salt.
Teacher's Tip: The average salinity is 35 parts per thousand, which is like putting 7 teaspoons of salt in a liter of water.
Exam Tip: Don't forget to include the percentage symbol (%) or "parts per thousand" to get full marks for the value.

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.
While we see waves on top, deep under the surface, the water moves because cold, salty water is heavy and sinks. This creates a deep-sea current that acts like a global conveyor belt, moving water all around the world.
Teacher's Tip: Remember that "Cold + Salty = Heavy," which makes the water sink and move below the surface.
Exam Tip: Make sure to list "Temperature" and "Salinity" specifically, as these are the main drivers of subsurface (underwater) movement.

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.
Generally, cold water is more dense and sinks, while warm water is less dense and stays on top. However, if warm water evaporates quickly, it leaves behind so much salt that it becomes very dense and sinks anyway.
Teacher's Tip: Think of density as how "crowded" the water molecules are; salt and cold both make them more crowded.
Exam Tip: Explain that high temperature causes evaporation, which increases salinity and therefore increases density.

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.
Waves are mostly caused by the wind blowing across the surface and they happen every few seconds. Tides are caused by the Moon's gravity and happen on a very slow, predictable schedule twice a day.
Teacher's Tip: Waves are like "surface ripples," while tides are the "entire ocean rising and falling."
Exam Tip: Focus your answer on the cause: Waves = Wind; Tides = Gravitational Pull.

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.
When the sun dries up water (evaporation), the salt stays behind, making the water heavy. When it rains (precipitation), the fresh water makes the ocean lighter, causing the water to shift and move to balance itself out.
Teacher's Tip: Imagine a see-saw; evaporation adds "weight" (salt) to one side, while rain takes it away.
Exam Tip: Use the words "Salinity" and "Density" to explain why the water sinks or flows.

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.
Because the Earth is spinning fast, it pushes the ocean water in the opposite direction, much like how you feel pushed back when a car suddenly starts moving. This effect, called the Coriolis effect, makes currents curve to the right in the north and to the left in the south.
Teacher's Tip: Think of a merry-go-round; if you try to walk in a straight line while it's spinning, you will naturally curve.
Exam Tip: Mention that the Earth rotates "West to East" to explain why currents move "East to West" near the equator.

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.
Inside the ocean, differences in how salty or how warm the water is create invisible "rivers" that flow for thousands of miles. This internal movement helps mix the ocean's nutrients and keeps the water from becoming stagnant.
Teacher's Tip: These are called "Endogenic" factors because they start *inside* the water itself.
Exam Tip: Be sure to distinguish these internal factors (like salinity) from external factors (like wind).

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.
As the Earth spins, one bulge of water is created by the Moon pulling on the side facing it, and another bulge happens on the opposite side due to centrifugal force. This means every place on Earth passes through two "high spots" and two "low spots" in the water every single day.
Teacher's Tip: Think of the ocean as an oval shape; as the Earth rotates inside that oval, we hit the high points twice.
Exam Tip: Use the word "meridian" and mention "Rotation of the Earth" to get full marks for the reasoning.

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.
The Moon doesn't sit still; it moves forward in its own orbit while the Earth spins. This means the Earth has to rotate a little bit extra each day to "catch up" to the Moon's new position.
Teacher's Tip: It's like two people racing; if the leader keeps moving, the person behind has to run longer to catch up.
Exam Tip: Remember: 52 minutes is the total daily delay, so 26 minutes is the delay for each individual high or low tide.

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.
Warm currents act like giant heaters that blow warm air over nearby land, preventing the weather from getting too freezing in the winter. This allows people to live and work in places that would otherwise be covered in ice.
Teacher's Tip: Think of warm currents as a "hot water bottle" for the continents they touch.
Exam Tip: Give the "Gulf Stream" as a specific example of a warm current to strengthen your answer.

Question 4: The eastern coasts of USA are comparatively cold.
Answer:
Due to the cooling effect of Labrador current keeps these coasts comparatively cold.
The Labrador Current brings freezing water straight down from the Arctic, which chills the air along the coastline. This makes the Northeastern USA much colder than European cities that are at the same distance from the equator.
Teacher's Tip: The Labrador Current is like an "Arctic breeze" that never stops blowing cold water south.
Exam Tip: Always mention the "Labrador Current" by name when discussing the cold eastern coast of the USA.

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.
When the cold Oyashio and warm Kurosio currents meet, they stir up nutrients from the bottom of the ocean. This "ocean mixing" creates a massive buffet for fish, leading to a huge population of sea life in that area.
Teacher's Tip: Mixing warm and cold water is like mixing ingredients for a cake; it creates the perfect environment for life to grow.
Exam Tip: Mention the "Kurosio Current" as the warm current that meets the Oyashio to explain the rich fishing grounds.

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.
Warm water evaporates easily and creates rain clouds, which is why Queensland is so wet. Cold water doesn't evaporate well, and when the wind blows from the dry land toward the sea, no rain ever reaches the Atacama desert.
Teacher's Tip: Warm currents = Rain; Cold currents = Dry Deserts. It's a simple but powerful rule!
Exam Tip: Contrast the "Warm East Australian Current" with the "Cold Peruvian Current" to explain the difference in rainfall.

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.
Even though Norway is very far north, the warm water from the North Atlantic Drift flows right past its harbors, keeping the water above freezing. Other places at the same latitude don't have this "warm bath," so their sea turns to solid ice.
Teacher's Tip: Norway stays open for business all year because of its "Atlantic heater."
Exam Tip: Use the term "North Atlantic Drift" to show you know the specific branch of the Gulf Stream that reaches Norway.

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.
The specific temperature and movement of these Pacific currents provide the perfect conditions for Salmon and other fish to thrive and migrate. These rich waters support huge fishing industries for both the USA and Canada.
Teacher's Tip: Currents don't just move water; they move the "food" that fish need to survive.
Exam Tip: Mention the "Salmon fish" specifically as it is a key characteristic of this region's fishing industry.

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.
Waves are short-term surface movements caused by wind, while tides are slow, massive rises and falls of the entire sea caused by gravity. Currents are like permanent "rivers" flowing through the ocean that stay on a fixed path regardless of the wind or tide.
Teacher's Tip: Waves are for surfing, Tides are for the clock, and Currents are for long journeys!
Exam Tip: To get full marks, define the "cause" for each: Wind for waves, Gravity for tides, and Temperature/Salinity/Rotation for currents.

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.
Tides happen because the Sun and Moon pull on the Earth's oceans like a tug-of-war. Spring tides are special "super-tides" that occur when the Sun and Moon team up in a straight line to pull the water as hard as they can.
Teacher's Tip: The name "Spring Tide" has nothing to do with the season; it comes from the water "springing" higher than usual.
Exam Tip: Always mention that Spring tides happen during both the "New Moon" and "Full Moon" phases.

Question 2: Differentiate between High Tides and Low Tides.
Answer:
High Tides :
1. When the sun and the earth and the moon are in the same line.
2. Caused when all the gravitational forces work together.
3. Occurs at the time of Full moon and new moon.
Low Tides :
1. When the sun and the earth and the moon are at the position of right angles.
2. Caused when the gravitational forces of the sun work against each other.
3. Occurs during the 8th day of each fortnight of a month.
High tides are when the water reaches its furthest point up the beach, while low tides are when the water retreats far back into the sea. This cycle repeats because of the way the Sun and Moon change their positions relative to the Earth.
Teacher's Tip: Think of high tide as the ocean "filling up" and low tide as it "emptying out."
Exam Tip: Use the term "right angles" to describe the position of the sun and moon during low (neap) tides.

Question 3: Describing the types of ocean currents, state and factors responsible for causing the currents.
Answer:
Ocean currents are warm and cold according to the temperature. Ocean currents are caused by the rotation of the earth, force of prevailing winds, amount of salinity and the presence of the continental ejections etc.
Currents are classified mainly by their temperature, which depends on where they start—near the equator (warm) or near the poles (cold). They are pushed along by global winds and steered by the way the Earth spins and the shape of the continents.
Teacher's Tip: Imagine the ocean is a giant bowl of soup; stirring it with a spoon (wind) and the bowl spinning (rotation) are what create the currents.
Exam Tip: List at least four factors (Rotation, Winds, Salinity, Temperature) to ensure a high score on this descriptive question.

Question 4: Describe the circulation pattern of the following three ocean currents.
(a) Labrador Current of the Atlantic Ocean.
(b) The Kuroshio current
(c) Oyashio Current of the Pacific Ocean.
(d) The North Atlantic Drift.
Answer:
(a) Labrador Current originates from the Arctic ocean along the coast of Labrador and passes touching Newfoundland continuing southwards along the coast of Nova Scotia. It is joined by West Greenland and Baffin Island Current. It meets the warm Gulf Stream Current at the Grand Banks, making this region the famous fishing bank.
(b) The Kuroshio current – is a strong western boundary current in the western north Pacific Ocean. It begins off the east coast of Taiwan and flows north-eastward past Japan, where it merges with the easterly drift of the North Pacific Current. It is analogous to the Gulf Stream in the Atlantic Ocean, transporting warm, tropical water northward towards the polar region. It is also sometimes known as the Black Stream — the English translation of Kuroshio, and an allusion to the deep blue of its water — and also as the Japan Current.
(c) Oyashio Current is a cold current colliding with warm Kuroshio current along the eastern coast of Japan. It originates in the Arctic ocean and passes through the Bering strait proceeding towards south.
(d) The North Atlantic Drift : It is the eastern extension of Gulf Stream to Europe as a warm current.
These four currents are part of a giant system that moves heat and cold around our planet's oceans. Some bring freezing Arctic water south, while others carry tropical warmth to the north, keeping our global climate in balance.
Teacher's Tip: Note that "Kuroshio" and "Gulf Stream" are twins—they both do the same job but in different oceans!
Exam Tip: Be precise about where each current starts (origin) and where it ends to show a complete understanding of its "pattern."

Question 5: Trace the origin and flow of the Gulf Stream. What is the effect of this current on the coasts of North America and Western Europe ?
Answer:
Gulf Stream – The Gulf Stream is one of the largest warm currents. It originates from the Gulf of Mexico (about 20°N) and moves in a north-easterly direction along the eastern coast of North America. The average speed is about 33 km per day and its average width is -about 70 km. Under the impact of the Westerlies, this warm current reaches the western coast of Europe (about 70°N latitude). The general direction of flow of the Gulf Stream, north of 30° N latitude, is northward. Near Newfoundland, its water mixes with the cold water of the Labrador Current, which forms very dense fog. The foggy conditions around Newfoundland hamper the navigation of ships. From here, the Gulf Stream moves north eastwards. This current gradually widens and its speed decreases. It becomes a prominent, slow-moving current known as the North Atlantic Driff. Near western Europe, it splits into two parts. One part moves northwards, past UK and Norway, while the other part is deflected southwards as the cold Canary Current. The warm water of the Gulf Stream modifies the weather conditions off the eastern coast of North America and the western coast of Europe.
The Gulf Stream is a massive warm water highway that starts in the tropics and journeys all the way to the Arctic. It is famous for creating thick fog when it hits cold water and for keeping Europe much warmer than it should be.
Teacher's Tip: Remember the transition: it starts as the fast "Gulf Stream" and slows down to become the "North Atlantic Drift."
Exam Tip: Mention the "Gulf of Mexico" as its starting point and explain its warming effect on Norway and the UK.

Question 6: Describe four major effects of currents.
Answer:
Major effects of currents are visualised by the distinct effect of the Worm Gulf Stream on the climate of eastern. North . American region and the western region of Europe and the oceanic trade routes joining the most industrialised regions of the world. On the other hand cold current of Benguela keeps the South African Western Coast mild and cool. Kurosio warm current keeps the eastern coast of Japan ideal for fishing.
Ocean currents control the world's weather, helping to heat up cold lands and cool down hot ones. They also create the world's best fishing spots and provide "highways" that ships use to travel faster across the sea.
Teacher's Tip: Think of currents as Earth's climate control system and its most important transportation routes.
Exam Tip: To list four effects clearly, focus on: 1. Climate, 2. Fishing, 3. Trade/Navigation, and 4. Desert formation.