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NCERT Class 7 Social Science Chapter 25 Water
Also, you can read the NCERT book online in these sections Solutions by Expert Teachers as per Central Board of Secondary Education (CBSE) Book guidelines. CBSE Class 7 Social Science Solutions are part of All Subject Solutions. Here we have given NCERT Class 7 Social Science Chapter 25 Water and After, NCERT Class 7 Social Science Textbook of Our Pasts – II: History, Social and Political Life – II: Civics, Our Environment: Geography. for All Chapters, You can practice these here.
Water
Chapter: 25
Our Environment [Geography]
QUESTIONS WITH ANSWERS
I. Answer the following questions:
(i) What is precipitation?
Ans: Falling of moisture in the form of rainfall, snow, fog, sleet and hailstone is known as precipitation.
(ii) What is water cycle?
Ans: The cycle of evaporation, condensation and precipitation never ending is known as water cycle. It is also called hydrological cycle.
(iii) What are the factors affecting the height of the waves?
Ans: The factors affecting the height of the waves are:
(a) Wind.
(b) Earthquake.
(c) Volcanic eruption.
(d) Underwater landslide.
(iv) Which factors effect the movement of waves?
Ans: The factors which effect the movement of waves are:
(i) Temperature.
(ii) Winds.
(iii) Gravitational pull of the sun.
(iv) The earth.
(v) The moon.
(vi) The warm and cold currents.
(v) What are tides and how are they caused?
Ans: The periodic rise and fall of the water level which occur at regular interval twice a day are called tides. Tides are of two types:
(a) Low tide. and
(b) High tide.
Tides are caused by the gravitational pull of the moon and the sun.
Fig. Occurrence of Tide
(vi) What are ocean currents?
Ans: Ocean currents are streams of water flowing constantly through the oceans in a definite directions. They are caused by:
(a) Variation in temperature of ocean water.
(b) The rotation of the earth.
(c) The prevailing winds.
(d) The shape of the land.
II. Give reasons:
(i) Ocean water is salty.
Ans: Ocean water is salty as it contains large amount of dissolved salt. Most of the salt is sodium chloride (NaCl) or the common table salt.
(ii) The quality of water is deteriorating.
Ans: The quality of water is deteriorating:
(a) As it is injudiciously used.
(b) As industrial effluents and untreated water get mixed into river stream.
(c) As sewage water also get mixed into these river bodies.
III. Tick the correct answer:
(i) The process by which water continually changes in its form and circulates between oceans, atmosphere and land is
(a) Water cycle.
(b) Tides.
(c) Ocean currents.
Ans: (a) Water cycle.
(ii) Generally the warm ocean currents originate near
(a) Poles.
(b) Equator.
(c) None of these.
Ans: (b) Equator.
(iii) The rhythmic rise and fall of ocean water twice in a day is called
(a) Tide.
(b) Ocean current.
(c) Wave.
Ans: (a) Tide.
IV. Match the following:
Ans:
| (i) Caspian | (c) Largest lake. |
| (ii) Tide | (d) Periodic rise and fall of water. |
| (iii) Tsunami | (b) Strong seismic waves. |
| (iv) Ocean currents | (a) Streams of water moving in a definite path. |
V. For Fun:
Be a Detective
(i) The name of one river is hidden in each of the sentences below. Spot it.
Example: Mandra, Vijayalakshmi and Surinder are my best friends.
Ans: Ravi.
(a) The snake charmer’s bustee, stables where horses are housed, and the piles of wood, all caught fire accidentally. (Hint: Another name for River Brahmaputra)
(b) The conference manager put pad, material for reading and a pencil for each participant. (Hint: A distributary on the Ganga- Brahmaputra delta)
(c) Either jealousy or anger cause a person’s fall. (Hint: Name of a juicy fruit!)
(d) Bhavani germinated the seeds in a pot. (Hint: Look for her in West Africa)
(e) “I am a zonal champion now” declared the excited athletic. (Hint: The river that has the biggest basin in the world)
(f) The tiffin-box rolled down and all the food fell in dusty potholes. (Hint: Rises in India and journeys through Pakistan)
(g) Malini leaned against the pole when she felt that she was going to faint. (Hint: Her delta in Egypt is famous)
(h) Samantha mesmerised everybody with her magic tricks. (Hint: London is situated on her estuary)
(i) “In this neighbourhood, please don’t yell! Owners of these houses like to have peace”. Warned my father when we moved into our new flat”. (Hint: colour!)
(j) Write the following words, Marc!’ “On”, “go”, “in” ….. said the teacher to the little boy in KG Class. (Hint: Rhymes with “bongo”)
Now make some more on your own and ask your classmates to spot the hidden name. You can do this with any name: that of a lake, mountains, trees, fruits, school items etc.
Hint: Do yourself with the help of your teacher.
Ans: (a) Teesta.
(b) Padma.
(c) Orange.
(d) Niger.
(e) Amazon.
(f) Indus
(g) Nile.
(h) Thames.
(i) Yellow.
(j) Congo.
Carry on Detective
(ii) With the help of an atlas, draw each river which you discovered in For fun (i), on an outline map of the world.
Hint: Do yourself.
SOME OTHER IMPORTANT QUESTIONS FOR EXAMINATION
Very Short Answer Type Questions
Q.1. What causes evaporation of water vapour?
Ans: The sun’s heat causes evaporation of water vapour.
Q.2. Define the concept Terrarium.
Ans: The concept Terrarium refers to artificial enclosure for keeping small house plants.
Q.3. What are the major sources of fresh water?
Ans: The major sources of fresh water are rivers, ponds, springs and glaciers.
Q.4. Which is the largest salt water lake in the world?
Ans: Caspian Sea is the largest salt water lake in the world.
Q.5. What are three main components of Hydrological or Water Cycle?
Ans: Three main components of Hydrological or Water Cycle are evaporation, condensation and precipitation.
Q.6. Define condensation nuclei.
Ans: Water vapour condenses only around some surfaces like dust particles in air are called condensation nuclei.
Q.7. Why rainwater called freshwater?
Ans: The rainwater is the purest form of water because during evaporation all particulate matter including salts are left behind. That is why it is also called freshwater.
Q.8. What is Salinity?
Ans: Salinity is the measure of salt content in water.
Q.9. What is a sea wave?
Ans: Rhythmic rise and fall of ocean water surface is known as sea wave.
Q.10. What is mean by ocean current?
Ans: A stream of water moving along a known path from one part of the ocean to another.
Q.10. Which day is celebrated as World Water Day?
Ans: World Water Day is celebrated on March 22.
Q.12. How waves are formed?
Ans: Waves are formed when winds scrape across the ocean surface. The stronger the wind blows, the bigger the wave becomes.
Q.13. What are tides?
Ans: The rhythmic rise and fall of ocean water twice in a day is called a tide.
Q.14. What is the meaning of Tsunami?
Ans: Tsunami is a Japanese word that means “Harbour waves” as the harbours get destroyed whenever there is tsunami.
Short Answer Type Questions
Q.1. What is tsunami?
Ans: During a storm, the winds blow at very high speed forming huge waves. These waves may cause tremendous loss to life and property. An earthquake, a volcanic eruption or underwater landslides can shift large amounts of ocean water. It results in the formation of a huge tidal wave known as tsunami. These waves may be as high as 15 m or above. The largest tsunami ever measured was 150 m high. These waves can travel at a speed of more than 700 km. per hour.
Q.2. Give any three reasons to show how are tides useful to us.
Ans: Tides are useful to us in many ways:
(i) They help in navigation, trade and fishing.
(ii) During high tide, the depth of water near the coast increases which helps. the big ships to enter or leave the harbour safely.
(iii) Tides, also, take away the mud brought down by rivers and prevent silting of harbours.
Q.3. How is hydrosphere useful to us?
Ans: Hydrosphere is useful to us in many ways as:
(i) It regulates the temperature of the earth.
(ii) Its the source of water vapour which forms clouds which help to cause rainfall on the earth.
(iii) Oceans are a major source of food for the mankind and an excellent mode of transport for bulk cargo.
Q.4. Name and explain the types of ocean currents.
Ans: There are two types of ocean currents. These are
(i) Warm currents. and
(ii) Cold currents.
(i) Warm currents flow from low latitudes to high latitudes and cold currents flow from high to low latitudes. Warm currents are not too hot than the surrounding water. Warmer currents have a temperature slightly higher than the surrounding water.
(ii) Cold currents have a temperature slightly lower than the surrounding water. Currents flowing along the western coasts of Africa, Australia and South America are cold currents and those flowing on the eastern coast are warm currents.
Q.5. Our earth is our water budget. Justify, how?
Ans: Total quantity of water is almost constant. The rate of glacial ice melted in summer will be almost equal to the rate of glacial ice formed during winters. In some areas, due to global warming melting of ice is greater than formation of ice leading to rise in the sea level. Whereas in other areas, evaporation rate is more than precipitation rate resulting in water scarcity or drought like situations. But at the global level, a state of equilibrium is, however maintained.
Q.6. Write any three physical properties of water.
Ans: Three physical properties of water:
(i) Water is the only substance that occurs naturally on the earth in its three states solid, liquid and gas. Water expands when it freezes.
(ii) The molecules of water collide with one another when heated and forms vapour.
(iii) Water has high surface tension. This enables the water surface to support small things like water bugs.
Q.7. Explain high tide and low tide.
Ans: It is high tide when water covers much of the shore by rising to its highest level. It is low tide when water falls to its lowest level and recedes from the shore.
Q.8. Where can we find the best fishing grounds of the world? Give examples as well.
Ans: The areas where the warm and cold currents meet provide the best fishing grounds of the world. Seas around Japan and the eastern coast of North America are such examples.
Q.9. Name the factors that determine the size of the waves.
Ans: The size of a wave depends on:
(a) The distance the wind blows over open surface of water.
(b) The length of time the wind blows.
(c) The speed of the wind.
Q.10. What are the harmful effects of waves?
Ans: Waves may cause tremendous destruction. An earthquakes, a volcanic eruption or underwater landslides can shift large amounts of ocean water. As a result a huge tidal wave called tsunami, that may be as high as 15 m is formed.
Long Answer Type Questions
Q.1. Which planet on the earth is called a watery planet? Describe the distribution of water on the earth.
Ans: Our earth is the planet. Its called so because it contains water in abundance. Three-fourth of the earth’s total surface is covered with water.
Distribution: Water is unevenly distributed on the surface of the earth. Ocean contains about 97 per cent of the total water available on the earth’s surface. The remaining three per cent is the fresh water. Its (fresh water) found in the form of snow and ice on the ground and in lakes and rivers.
Q.2. How are tides caused? Name two types of tides. How they are caused?
Ans: The strong gravitational pull exerted by the sun and the moon on the earth’s surface causes the tides. Two types of tides are – tides. spring (high) tides and neap tides.
When the water of the earth closer to the moon gets pulled under the influence of the moon’s gravitational force, it causes high tide. During the full moon and new moon days, the tides are highest. These tides are also called spring tides.
When the moon is in its first and last quarter, the ocean waters get drawn in diagonally opposite directions by the gravitational pull of sun and earth resulting in low tides. These tides are called neap tides.
Q.3. Why Tsunami of December 2004 is called a killer wave?
Ans: On December 25, 2004, a massive undersea earthquake triggered a tsunami not far from Banda Aceh, a coastal town in South Sumatra, a major island of Indonesia. The intensity of the earthquake was the highest recorded in history. The Tsunami waves generated by this earthquake travelled westward. The impact was felt in 14 countries as far away as the east coast of Africa. More than 300,000 persons, most of them in Indonesia and 10,000 in India, fell victim to the ‘killer waves’. There was damage to life and property worth billions of rupees.
Q.4. Describe any importance of Ocean Currents.
Ans: Importance of Ocean Currents is listed below:
(i) Ocean currents influence and moderate the climate of the coastal regions. Warm current increases and cold current decreases the temperature of the coastal regions.
(ii) Rainfall is quite common in landmasses closer to warm currents while areas near cold currents do not have much rainfall.
(iii) When a warm current meets a cold current growth of planktons take place. This attracts a lot of fish and the areas become great fishing grounds like Great Fishing Bank (Newfoundland).
(iv) It also helps in navigation by preventing water in ports from freezing during winters. Norwegian coast is in the Polar region but it does not freeze in winter due to the warm North Atlantic Drift.
Q.5. What is the difference between Fresh and Saline Water?
Ans:
Higher Order Thinking Skill
Q.1. Under what conditions high tides are produced?
Ans: When the earth, moon and the sun are in straight line. This occurs twice a month. These occasions are New Moon and Full Moon.
Q.2. The oceans are interconnected and water in oceans is in constant motion. Explain.
Ans: There are many factors that contribute to this movement such as the following:
(i) Winds, which cause drag on the surface of ocean water known as surface ocean currents.
(ii) The difference in salinity and the resulting density variation.
(iii) The temperature variation.
Consequent to the above factors, ocean water moves both horizontally and vertically.
Three types of movements can be seen as:
(i) Ocean currents.
(ii) Tides.
(iii) Waves.
Q.3. How the height of wave is determined?
Ans: The height of wave is determined by:
(i) The length of time for wind has blown over the water.
(ii) Distance of open water which wind has blown called fetch.
(iii) Wind speed.
Value Based Questions
Q.1. How water is useful to us?
Ans: Water is useful to us as all life forms on the earth cannot exist without the absence of water. It is required by all human beings for survival.
Q.2. How does ocean current influence?
Ans: Ocean currents influence as following way:
(i) It influence the climate of a place by raising/lowering temperature.
(ii) Where warm and cold current meet there is plenty of fish making the region a rich fishing ground.
(iii) Meeting of warm and cold current leads to heavy condensation and produces intense fog, which cause a major problem for shipping.
MAP SKILL
1. On a physical world map, mark and name the following:
(i) Caspian Sea.
(ii) Mississippi.
(iii) Amazon River.
(iv) Lake Victoria.
(v) Orange River.
(vi) Coral Sea.
Ans:
2. On the map of world show the following:
Warm Currents:
(a) North Pacific Drift.
(b) Gulf-Stream.
(c) North Atlantic Drift.
(d) Equador Current.
(e) South Equatorial Current.
Cold Currents:
(a) Peru Current.
(b) West Wind Drift.
(c) West Australian Current.
(d) Oyashio Current.
(e) Labrador Current.
Ans:
OBJECTIVE TYPE QUESTIONS
1. Fill in the blanks:
1. The ammant of salt dissolved in the sea water is called _____.
Ans: Salinity.
2. Water get renewed (recharged) through a process called _______.
Ans: Water cycle.
3. Tides are caused by _______ toward the earth.
Ans: Gravitational pull of the moon and sun.
4. The earth consist of _______ % of water.
Ans: 78.
5. High tides are also called ______ tiders.
Ans: Spring.
II. Tick the correct (✓) and cross (x) the wrong statements:
1. Low tides are useful in navigation.
Ans: (×).
2. The Indira point got submerged in the Tsunami during 2004.
Ans: (✓).
3. The gravitation pull of the moon and the sun is the major cause of the tide.
Ans: (✓).
4. The largest tsunami ever measured was 700 m high.
Ans: (×).
5. Low tides help in navigation.
Ans: (×).
6. Californian current flow to the east of North America.
Ans: (✓).
7. Labrador current is an example of cold current.
Ans: (✓).
Multiple Choice Questions
Choose the correct option:
1. Which of the following day is celebrated as World Water Day?
(a) March 22.
(b) May 18.
(c) July 9.
(d) September 7.
Ans: (a) March 22.
2. Where does cold current originate?
(a) Near poles.
(b) Near equator.
(c) Near Tropic of Cancer.
(d) Near Tropic of Capricorn.
Ans: (d) Near Tropic of Capricorn.
3. Largest water bodies on the earth are:
(a) Rivers.
(b) Seas.
(c) Lakes.
(d) Oceans.
Ans: (d) Oceans.
4. Constant movement of ocean water in a particular direction is called:
(a) Waves.
(b) Ocean current.
(c) Tide.
(d) None of the above.
Ans: (a) Waves.
5. Which of these is an example of warm ocean current?
(a) Californian current.
(b) Peru current.
(c) Canary current.
(d) Norwegian current.
Ans: (d) Norwegian current.
