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ICSE Solutions for Class 9 Geography – Earthquakes

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Exercises

I. Fill in the blanks below

1. Most earthquakes occur on account of the strain in the earth’s crust.
2. P (primary or push waves) are the first earthquake waves to be recorded on a seismograph of an earthquake.
3. The last of the earthquake waves to arrive on the surface of the earth are L (surface or long) waves.
4. The giant sea waves caused by earthquakes in the oceans are called Tsunamis.
5. About 70 per cent of the earthquakes occur in the Circum- Pacific-Mountain Belt.

II. Short Answer Questions

Question 1.
What is called an earthquake ?
Answer:
An earthquake is defined as a tremor below the surface of the earth which causes shaking of the earth.

Question 2.
State two natural causes of an earthquake.
Answer:
Natural causes are the movement of tectonic plates and volcanic activities.

Question 3.
Name one man-made cause of an earthquake.
Answer:
Construction of large scale dams, thrust of rivers along fault lines, dumping of chemical wastes also cause earthquakes due to imbalance in isostatic balance of the earth’s landforms, e.g. Koyna dam caused an earthquake in Maharashtra.

Question 4.
What are known as seismic focus and epiceptre with respect to an earthquake ?
Answer:
The point of origin of earthquake waves is called seismic focus and the centre vertically above the seismic focus nearest to the earth’s crust is called epicentre.

Question 5.
What is known as Richter scale ? State its uses.
Answer:
Ritcher scale is used to measure the intensity of earthquake through a scale, which is motivated by a needle attached to this instrument The zigzag wavelength of the earthquake comes on the screen and calculated from 1 to 9 scale measured in centimetres.

Question 6.
How are earthquakes useful ?
Answer:
Earthquakes cause energy release to put the earth in good shape; several landforms are uplifted to build large plains e.g. Sagami Bay uplifted 200 m, Landslides cause the formation of lakes in Himalayan region.

Question 7.
Give any two destructive effects of earthquakes ?
Answer:
Destructive effects are collapse of structures, submergence of coastal parts e.g. Dwarka submergence, these change the course of rivers, danger to human life and motivation of tsunami waves causing drastic calamities.

Question 8.
What is tsunami ? How is it caused ?
Answer:
Tsunami is a large furious destructive sea waves caused by the force of an earthquake along the moving tectonic plates, volcanic activity landslides and meteorite impact.

Question 9.
How do Japanese predict earthquakes ?
Answer:
Japanese use the methods of measuring changes in sea level and variations in Earth’s magnetic field to predict earthquakes.

Question 10.
Name the two belts where most of the earthquakes occur.
Answer:
Two belts are the Circum-Pacific Mountain belt and the midworld mountain belt of high fold mountains like the Alps, Himalayas etc.

III. Match the following

Answer:

IV. Long Answer Questions

Question 1.
Describe how earthquakes are caused on the surface of the earth.
Answer:
When the earth’s crust is unable to accommodate itself to the strain due to isostatic imbalance, so sudden release of energy results in violent shock or an earthquake. The earthquakes are caused by severe tectonic movement of plates, volcanic eruption forces and isostatic imbalance often taking place due to diastrophism creating ups and downs in landform construction.

Question 2.
Explain the three types of earthquake waves. What is the difference between seismic focus and epicentre ?
Answer:
Three types of earthquake waves are :

1. P-primary waves,
2. S-Secondary (or Shear waves) and
3. L-Long waves (or Surface waves).
   

Seismic focus.is located in the interior of earth’s crust from where the earthquake waves originate and the epicentre is the nearest point vertically below the region of earthquake effect.

P Q. What is the Tsunami ? How ist it produced ? What are its effects ?
Answer:
Tsunami is very destructive sea wave rising high upto several metres and jump furiously along the coastal areas like the hood of a snake. The name ‘tsunami’ is from the Japanese words : ‘Tsu’ and ‘nami’ meaning ‘harbour’ and ‘wave’ respectively. So tsunamis are harbour waves.
It is produced mainly by undersea earthquake along the gaps of tectonic plates, volcanic thrusts, great landslides and meteorite impact.
They can cause a lot of destruction on the shore. They are sometimes mistakenly called “tidal waves,” but tsunamis have nothing to do with the tides.

Question 3.
Compare and contrast the constructive effects and the – destructive effects of an earthquake.
Answer:
Constructive effects :

1. Earthquakes help the earth release its stored up energy. The majority of the earthquake occur around. The plate margins. This energy release helps to keep the earth in good shape.
2. On account of both vertical and lateral displacement of the earth’s crust, earth-quakes may raise or lower parts of earth especially near the seashore. Sagami Bay of Japan was uplifted 200 m in 1923.
3. Landslides triggered by earthquakes cause formation of lakes as has happened at many places in the Himalayan region.

Destructive effects :

1. Human beings have settlements in active earthquake zones. Most often the houses and other structures collapse causing great loss of property.
2. The forces of uplift and subsidence also cause submergence of coastal parts. For example: Dwarka in Gujarat which now lies submerged under the sea.
3. Earthquakes have changed the course of rivers in the past. They have thus rendered many areas unsuitable for irrigation and agriculture. They cause danger to human life.

Question 4.
Is it possible to predict an earthquake ? Give reasons to support your answer.
Answer:
No till now it is not possible to predict an earthquake. Earthquake prediction in the past was left to astrologers and mystics. Today it is a respectable scientific pursuit. The Russians were the first to discover P and S seismic waves in 1960s on the basis of which predictions were made. These waves still are the only means available to seismologists to predict earthquakes.
The theory of Plate Tectonics offers another means of prediction on scientific lines. Japanese use the methods of measuring changes in sea level and variations in Earth’s magnetic field to predict earthquakes. However, no method is still foolproof as has been proved by recent earthquakes in Japan, India and the USA.

Question 5.
How are earthquakes distributed over the globe ?
Answer:
The earthquakes are common along the weak tectonic belts affected by continuous tremors due to the movement of plates one upon another. Main belts are Circum-Pacific Mountain belt and Mid-World Mountain belt of fold mountains which are still in the process of upthrust forces increasing their height.

Question 6.
How is the intensity of earthquakes measured ? What instruments are used ?
Answer:
Ritcher scale and Mercalli scale are used to measure the intensity of earthquakes. Ritcher scale measures through a graphical scale in zigzag graph from 1 to 9 and Mercalli scale observes it from 1 to 12 points scale.

Practice Questions (Solved)

Question 1.
(a) What is an Earthquake ?
(b) How it is caused ?
(c) Describe the world’s distribution of earthquakes.
(d) What are the advantages and disadvantages of Earth quakes.
OR
What are the effects of Earthquakes ?
(e) Name the major earthquakes of India from 1991 to 1997.
Answer:
(a) The sudden mild or violent shaking of a part of the earth is called an earthquake. An earthquake is generally accompanied by a rumbling and tremors.
(b) Causes The chief known causes of earthquakes are believed to be as follows :

1. When a dormant volcano erupts into activity or an active volcano discharges matter with greater violence the surrounding areas feel tremors or earthquakes.
2. When the interior of the earth cools and contracts the outer crust in some places cracks and faults are caused. This movement causes earthquake.
3. Some time water percolates so deep down into the earth that it turns into steam on account of the internal heat. This steam expands and tries to force its way out. This pressure causes an earthquake.

(c) The earthquakes are distributed along two major belts namely circum Pacific earthquake belt (Ring of fire) and the Mid¬World, Mountain Earthquake belt along the great fold mountain zone.
(d) Earthquakes brings about changes on the surface of the earth which are very harmful to man.

Destructive Effects :

1. Many towns are destroyed and there is considerable loss of life and property.
2. They cause floods by uplifting of land in the’ course of river.
3. Some places are submerged under the sea.
4. Big cracks and fissures are formed on the surface of the river and they interrupt communications.
5. Some times rivers disappear or change their courses or get flooded. Railway lines are twisted.
6. They cause great tidal waves, which may bring havoc to the coastal areas.

Constructive Effects :

1. Precious metals and minerals come up to the surface for the use of man.
2. New lands for habitation above the surface of the sea are formed.
3. Some times new springs and water falls are formed which help in irrigation.
4. Violent earthquakes have led to the formation of hills and mountains.
5. Bays and gulfs are formed along the coastal land to provide new ports and harbours.

(e) Major earthquakes of India from 1991 to 1997

1. Latur -1991
2. Uttarkashi – 1993

Question 2.
Name the important Earthquake-belts of the world.
OR
Indicate two major belts of Earthquakes.
Answer:

1. Circum – Pacific Earthquake Belt :- i.e. round the Pacific Ocean. This belt goes along with the coast of America and East coast of Asia.
2. Mid World Mountain Earthquake Belt :- This belt runs through the middle of Asia from East and goes beyond the Mediterranean sea as far as the West Indies. This belt, however, is not so active as Pacific Belt.

Question 3.
Name the instrument used to record Earthquakes.
Answer:
The instrument used to record Earthquakes’ is called Seismograph.

Question 4.
Name some Earthquakes which caused great damage.
Answer:
Some Earthquakes which caused serious damage to property and life are :

1. Lisbon Earthquake of 1755
2. South Carolina Earthquake of August 1886
3. The Japan Earthquake of Oct. 28, 1891
4. Kanga (Himachal pradesh) Earthquake of April 1905
5. Tokyo (Japan) Sep. 1923
6. Quetta 1935
7. Bihar 1934
8. California Earthquake of April, 1966
9. Turkey Sep. 1975
10. Iran 1968
11. Peru 1970
12. Tangshan (China) Earthquake of July, 1976
13. Broach Earthquake of 1970 affected part of Gujrat.
14. Earthquake of 1988, had its epicentre near Darbhanga and affected parts of North Bihar, Nepal and Bangladesh.
15. The Bhuj earthquake of 2001 devastated many cities of Gujarat.

Question 5.
Earthquakes occur in the Mid-Atlantic belt.
Answer:
Earthquakes occur in the Mid-Atlantic belt because here the sea floor spreading is the main cause for earthquakes.

Question 6.
How do earthquakes affect landscape ?
Answer:
Earthquakes cause rise and fall of landmasses, create fault scarps, offset streams and other land features and cause landslides. Earthquakes waves also destroy houses and man-made structures, buckle and twist the railway lines electric and telegraph lines etc.

Question 7.
What was the cause of Koyna earthquake in India ?
Answer:
Koyna Dam is located in Maharashtra on the Deccan plateau. This part was considered a stable block free from earthquakes. But Koyna earthquake in 1986 was a big surprise. In the reservoir of the dam water gathered was more than its capacity. It disturbed the local isostatic balance. It caused an earthquake and caused cracks in the rocks. It may be called a man-made earthquake.

Question 8.
Describe the main type of Earthquake Waves.
Answer:
Earthquake Waves :- Earthquake waves travels in all directions from the Focus. There are three types of earthquake waves :

1. Longitudinal Waves : These are known as Primary Waves ‘P’
2. Transverse Waves : These are known as Secondary Waves ‘S’.
3. Surface Waves : These are called Long Waves or ‘L’ Waves.

Question 9.
Name the causes of earthquakes.
Answer:

1. Volcanic eruptions
2. Faulting
3. Elasticity of rocks
4. Local causes
5. Epeiro, Genetic events.

Question 10.
Why are earthquakes related to volcanoes ?
Answer:
There is a close relationship between an earthquake and a volcano. Earthquakes and volcanoes occur in small belts, i.e. Mid world belt and Circum pacific belt. Their distribution shows a similar pattern. Volcanic eruption lead to earthquakes. Volcanic eruptions are the local cause of earthquakes.

ICSE Solutions for Class 9 Geography – Rocks

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Exercises

I. Short Answer Questions 

Question 1.
State two points of distinction between rocks and minerals.
Answer:
Rocks :

1. Rocks contain minerals.
2. Rocks are the aggregates of minerals and other rock material.

Minerals :

1. Minerals do not contain rocks.
2. Mineral are the compounds of pure elements with a definite chemical Composition.

Question 2.
Name any three elements of the earth’s crust.
Answer:
These are silicon, aluminium, iron, magnesium, calcium, potassium, sodium and nickel.

Question 3.
Name three types of rocks.
Answer:
Three types of rocks are sedimentary, igneous and metamorphic rocks.

Question 4.
Why are the igneous rocks also called the primary rocks?
Answer:
The igneous rocks were the first to be formed. They form the basis of formation of other types of rocks. Thus, they are called primary rocks.

Question 5.
Give one difference between Extrusive igneous and Intrusive igneous rocks.
Answer:

• Extrusive igneous rocks are formed by the cooling of molten magma on the earth’s surface.
• Intrusive igneous rocks are formed when the magma solidifies within the earth’s crust forming coarse texture.

Question 6.
Name any two chief characteristics of Igneous Rocks.
Answer:
Igneous rocks are formed by cooling of magma and these are crystalline rocks and full of mineral compounds.

Question 7.
What is the main characteristics of Basic Igneous Rocks?
Answer:
Basic igneous rocks have higher percentage of oxides of denser elements and dark in colour, e.g. Basalt, dolerite etc.

Question 8.
Name two important landforms made by Igneous Rocks.
Answer:
Conical mountains and extensive lava plateaus.

Question 9.
What are Sills ?
Answer:
The magma takes place in between the layers of rocks and hardens after cooling, which is called Sill.

Question 10.
Which rocks are associated with ores of metals ?
Answer:
Igneous rocks are associated with ores of metals due to their origin by cooling magma resulting in crystalline rocks rich in mineral content.

Question 11.
Which rocks are associated with fossil fuels ?
Answer:
Sedimentary rocks are associated with fossil fuels due to fossils trapped in between layers of these rocks.

Question 12.
Mention any two chief characteristics of Sedimentary Rocks.
Answer:

• Sedimentary rocks are formed from material derived from other rocks including plant and animal remains. These rocks thus contain fossils.
• Sedimentary rocks are generally not crystalline. They are soft and layered as they are formed by deposition of sediments.

Question 13.
Give two examples of Sedimentary Rocks.
Answer:

1. Sandstone
2. Limestone

Question 14.
Name the rocks which are most widespread on the earth.
Answer:
Sedimentary rocks are most widespread on the earth.

Question 15.
Name the three stages of lithification of Sedimentary rocks.
Answer:
Lithification is the process of turning loose rock material into hard rock through evaporation, compaction and cementation.

Question 16.
Name the types Sedimentary rocks based on agents of formation.
Answer:
There are five main types of rocks on the basis of agents of formation:

1. Riverine Rocks These are formed by the sediments deposited by running water or river.
2. Lacustrine Rocks These are formed by the deposition of silt etc on the bed of lakes.
3. Glacial Rocks These are formed by the debris carried on and deposited by glaciers.
4. Aeolean Rocks These are formed by the deposition sand accumulation by the wind.
5. Marine Rocks These are formed by the deposition of sediments at the ocean floor. These types are Calcarious and Carbonaceous sedimentary Rocks.

Question 17.
Which agents are responsible for deposition of sediments?
Answer:
There are three main agents of deposition i.e., water, wind and ice, which mainly act as agents of change on the surface of earth for deposition of sediments.

Question 18.
What are known as metamorphic rocks ? Give two examples.
Answer:
Metamorphic rocks are formed by complete change of texture of rocks through volcanism and diastrophism, e.g., limestone is converted to marble and shale is transformed to slate.

Question 19.
What is Mechanical Metamorphism ?
Answer:
This is a mechanical Transformation in which texture of rocks is changed by crushing and rubbing processes associated with heat and compression created by mechanical action.

Question 20.
What is meant by Rock Cycle ?
Answer:
The earth is said to be 4700 million years old and the rocks came into existence 3400 years ago. Since then these rocks have undergone various changes by which multiple transformation took place within the rocks. This continuous process of transformation of old rocks into new rocks is known as rock cycle for figure See Page no. of this book.

Question 21.
What processes are involved in the formation of Igneous Rocks ?
Answer:
Igneous rocks are associated with volcanic activity, cooling of magma and mechanical weathering etc.

II. Explain these terms associated with rocks.

Question 1.
Extrusive Igneous Rocks.
Answer:
These rocks are formed by consolidation of erupted magma on the surface of earth.

Question 2.
Laccoliths and Batholiths.
Answer:
Laccoliths is formed by the intrusion of magma in the erupting channel just below the crust. Batholiths are deep seated dome shaped formation of magma intrusion, generally forming the base of mountain ranges, e.g., Ranchi Batholiths.

Question 3.
Fossil fuels.
Answer:
These are the fuels accumulated between two impermeable layers of the sedimentary rocks, e.g. peat, coal and petroleum etc.

Question 4.
Lithification of Rocks.
Answer:
It is the process of turning the loose material into hard rock, which helps in the formation of the sedimentary rocks found in different layers one upon another.

Question 5.
Metamorphism.
Answer:
It is the process of transformation of sedimentary and igneous rocks into metamorphic rocks through extreme temperature and compression by volcanism and diatrophism by physical and Chemical changes.

III. Distinguish between each of the following

P Q. Lava and Magma.
Answer:
Lava : Lava is the black molten material erupted in a volcano.
Magma : Magma is the compound of lava, stones, ash, debris etc. erupting out in a volcano.

Question 1.
Plutonic and Volcanic rocks.
Answer:
Plutonic rocks :

1. These are intrusive igneous rocks.
2. These cool down very slowly due to heat in the interior

Volcanic rocks :

1. These are extrusive igneous rocks.
2. These cool down abruptly due to less temperature on the surface region.

Question 2.
Thermal and Dynamic Metamorphism.
Answer:
Thermal Metamorphism :

1. It takes place due to extreme temperature which transforms the shape and texture of rocks.
2. The heat may be due to hot magma or friction of rocks.

Dynamic Metamorphism :

1. It takes place due to excessive compression created by tectonic forces within the earth.
2. It takes place through physical or chemical changes by deep pressure.

Question 3.
Sills and Dykes.
Answer:
Sills : The collection of magma between layers of rocks is called sill.
Dykes : The fillings of magma in the cracks or fissures of rocks are called dykes.

Question 4.
Calcarious and Carbonacious rocks.
Answer:
Calcarious rocks : The sedimentary rocks formed by the deposition of shells, skeletons of sea organism as corals, clams and oysters etc. are called calcarious rocks due to excess of calcium.
Carbonacious rocks : The sedimentary rocks formed by the deposition of large scale vegetation and animals etc. are called carbonacious rocks due to the excess of carbon.

Question 5.
Acid Igneous Rocks and Basic Igneous Rocks.
Answer:
Acid Igneous rocks : These are lighter rocks with silica content 65 to 85 percent with density less than 2 g/Cm³, e.g. Granite.
Basic igneous rocks : These are denser rocks with silica content 40 to 60 percent with average density between 2.8 g/Cm³ and 3.0 g/Cm³ e.g. Basalt.

IV. State the types of rocks for the formation of which the following processes are involved.

Question 1.
Solidification of magma on the surface of the earth.
Answer:
Extrusive igneous rocks

Question 2.
Formation of large crystals, coarse texture and slow cooling and compaction.
Answer:
Intrusive igneous rocks.

Question 3.
Accumulation takes place over long periods of time in seas, lakes and streams.
Answer:
Sedimentary rocks.

Question 4.
Decomposition of organic matter at different stages and over different periods of time.
Answer:
Carbonaceous Sedimentary rocks.

V. Long Answer Questions

Question 1.
Distinguish between rocks and minerals.
Answer:
The rocks contain minerals in the form of ores, but minerals do not contain rocks. Sedimentary rocks contain fossil fuels like coal and petroleum etc, igneous rocks are rich in minerals like copper, gold, iron etc, metamorphic rocks contain valuable building stones like marble and garnet, feldspar etc. Rocks have no definite chemical composition, while minerals have particular chemical composition.

Question 2.
Describe how are igneous rocks formed ? State their chief characteristics.
Answer:
Igneous rocks are formed by melting and cooling of magma originated from volcanic eruptions. These may be formed by diastrophism and volcanism. These rocks are strong, crystalline and dark in colour. These may be extrusive and intrusive on the surface and beneath the crust respectively.

Question 3.
How are igneous rocks classified on the basis of their chemical composition?
Answer:
On the basis of chemical composition igneous rocks may be classified into two groups i.e. Acid igneous rocks and Basic igneous rocks. Acid rocks have silica content 65-85 percent e.g. granite which is made up of large crystals of quartz, feldspar and mica. Basic rocks contain high percentage oxides of denser material, silica content is between 40-60 percent with a density of 2.8 g/cm³ and 3.0 g/cm³. Acid rocks are lighter than Basic rocks.

Question 4.
Classify the igneous rocks on the basis of their place of origin.
Answer:
On the basis of origin igneous rocks are divided into two groups i.e. Extrusive and Instrusive igneous rocks. Extrusive igneous rocks are found on the surface of the earth by cooling down of erupted magma. Intrusive igneous rocks are formed beneath the earth’s crust after solidification of magma.

Question 5.
How are sedimentary rocks formed ?
Answer:
Continuous deposition of sediments of silt, soil, debris etc. by water, wind and ice along lower landforms and solidification into different layers result in the formation of light sedimentary rocks.

Question 6.
Explain the formation of sedimentary rocks on the basis of agents of formation.
Answer:
There are five main types of rocks on the basis of agents of formation:

1. Riverine Rocks These are formed by the sediments deposited by running water or river.
2. Lacustrine Rocks These are formed by the deposition of silt etc on the bed of lakes.
3. Glacial Rocks These are formed by the debris carried oh and deposited by glaciers.
4. Aeolean Rocks These are formed by the deposition sand accumulation by the wind.
5. Marine Rocks These are formed by the deposition of sediments at the ocean floor. These types are Calcarious and Carbonaceous sedimentary Rocks.

Question 7.
How are sedimentary rocks classified on the basis of their formation ?
Answer:
There are three types of this type of rocks :

1. Mechanically formed rocks : Denudation of rocks by agents of change results in layers of sedimentary rocks by mechanism.
2. Chemically formed rocks : These are formed by evaporation of calcarious water and accumulated along lake and lagoon beds, e.g. gypsum and rock salt.
3. Organically formed rocks : These are formed by deposition of dead plants and animals e.g. limestone rock (or Calcareous rock) lignite, bituminous and anthracite coal are carbonaceous rocks formed by compression of vegetation under the layers of sedimentary rocks. In the same way petroleum in between the sedimentary rocks is the result of zurasic age dinosaurs e.g. shale rock, containing oil.

Question 8.
What is metamorphism ? What are its causes ?
Answer:
Metamorphism is a process of transformation of sedimentary and igneous rocks into the metamorphic rocks through physical and chemical reactions. Main causes are great temperature and pressure beneath the earth’s crust, which changes the original texture and form of the rocks into dense, crystalline and fine grained rocks.

Question 9.
What are the chief characteristics of metamorphic rocks?
Answer:
Metamorphic rocks are composed of fine particles and dense, smooth material. These are very precious rocks, particularly for building stones like marble, garnet, slate quartzite etc.

Question 10.
What is Rock Cycle. How does it keep the earth young?
Answer:
The earth is said to be 4700 million years old and the rocks came into existence 3400 years ago. Since then these rocks have undergone various changes by which multiple transformation took place within the rocks. This continuous process of transformation of old rocks into new rocks is known as rock cycle.

To keep the earth young, rock melts again resulting in formation of igneous rock. This disintegrated material again form sedimentary rock, it takes hundreds are thousands years.

Question 11.
Give a detailed account of lithiflcation of sedimentary rocks.
Answer:
Lithification means solidification. The loose material carried on by water, wind and ice is deposited slowly in different layers one upon another. Gradually the deposited sediments become solid and hard due to pressure and temperature. Evaporation results in the loss of water within the sediments and these are compacted and cemented. Compaction takes place by increasing weight and pressure of over lying sediments e.g. sand is converted to sandstone. Cementation takes place by bonding of compacted sediments by natural elements like calcium compounds, silica and iron with a property to bind the loose materials to solid state.

Practice Questions (Solved)

Question 1.
(a) What is meant by a rock ?
Or
What is meant by a ‘rock’ ? Name the main types of rocks.

(b) Differentiate between Rock and Mineral
(c) How are sedimentary and igneous rocks formed ?
(d) In what type of rocks do you find fossils and why ?
(e) How are rocks important to us ?

Answer:
(a) Rock : A rock can be defined as “an aggregate of minerals that forms a more or less definite unit of the earth’s crust”. A rock does not possess a definite composition like that of a chemical compounds, but is usually a mixture of various minerals.
The bulk of rocks is made up of silica or quartz and feldspar. Feldspar are composed of silica, aluminium, potassium and sodium or calcium. Some rocks are composed of grains cemented together, while several other are crystalline, compact or even glass-like.
All material (whether hard like stone or sand) of which the crust of the earth is composed are called rocks e.g, stone, clay, lava, sand, chalk, salt, coal marble etc.. On the basis of their mode of formation, rocks are divided into three types :

• Igneous rocks
• Sedimentary rocks
• Metamorphic rocks.

(b)
Rock :

1. A rock is a natural solid organic or inorganic material forming the crust of the earth.
2. A rock is an aggregate of minerals.
3. The physical properties of rocks vary.

Mineral :

1. The mineral is an organic element or compound which occurs naturally.
2. A mineral has an atomic structure.
3. It has fixed definite physical properties.

(c) Formation of Sedimentary rocks : Sedimentary rocks are formed by the process of consolidation of sediments deposited commonly in water bodies like seas or lakes. The sediments are derived by the rivers, glaciers, winds and waves. The sediments consist of loose particles of gravel, sand, silt and clay in various proportions. These loose particles get consolidated or compacted into hard rocks by the presence of cementing substances like lime or the pressure of overlying deposits.
Formation of igneous rocks : The rocks which are formed by the process of solidification of molten rock material (magma), are called igneous rocks.
The processes involved in the formation of igneous rocks are cooling and solidification.
Two types of igneous rocks are

• Intrusive igneous rocks
• Extrusive igneous rocks.

Formation of extrusive rocks : These rocks are also known as volcanic rocks, because they are formed by the solidification of lava on the earth’s surface. As on the outer surface of the earths’ crust the rate of cooling and solidification is more rapid than in the interior, the different minerals composing the magma have less time to become crystalline. The crystals formed are small. Basalt is a good example of this type of rock. Extrusive rocks are much more fine-grained as compared to intrusive granite. The hot magma free of gases is converted into lava on reaching the surface. It takes the form of lava flows, lava sheet and lava plateau. The north-western part of Peninsular India, known as the Deccan Trap, covers a great area of basaltic regur soil formed by the weathering of these rocks. Basaltic lava rocks cover a wide area in Columbia, the Snake Plateau of U.S.A. The other name of extrusive rock is Volcanic
Rock The properties of extrusive rocks :

1. These rocks are formed by the solidification of lava on the earth’s surface.
2. These rocks are very fine-grained.
3. They are usually dark coloured.

The other name given to intrusive rock is Plutonic rock.
Formation of intrusive rocks : When the molten material of the interior part of the earth’s crust finds its way through clefts or spaces that it has made by pushing the surrounding rocks apart, and does not reach the surface. This is known as the Intrusive Rocks. Dolerite and granite are the best examples of intrusive rocks.
Properties of intrusive rocks :

1. They have large crystals.
2. They are very compact.
3. They are glassy in appearance.

(d) Fossils are found in sedimentary rocks. Organic remains of plants and animals or their skeletal impressions are called fossils. Fossils help us in fixing the relative ages of rocks.
(e) The dead sea abounds in chemically formed sedimentary rock because the evaporation of water from it is rapid.

Question 2.
(a) Name different types of sedimentary rocks.
(b) What physical agents are involved in the sedimentary rocks ?
(c) How are chemically-formed sedimentary rocks produced?
(d) How are chemically-formed sedimentary rocks formed? Give examples.
(e) Sedimentary rocks are also called stratified rocks. Why?
OR
Why sedimentary rocks are called stratified rocks ?
Answer:

(a) There are three types of sedimentary rocks on the basis of the nature of sediments, their origin, composition and mode of formation. These are mechanically-formed sedimentary rocks, organically formed sedimentary rocks and chemically- formed sedimentary rocks.
(b) Rain water, wind, ice or the running water are the agents involved in the formation of sedimentary rocks. These agents break and carry on loose material and deposit it in various low lying areas to convert into the solid sedimentary rocks.
(c) Chemically-formed sedimentary rocks are produced through evaporation of water from solutions containing minerals. In this ways a rock like ‘gypsum’ is produced. Other examples are nitrates and potash etc.
(d) Chemically formed sedimentary rocks are formed through chemical action of water. Some mineral like limestones and salts are dissolved into the water and after the evaporation of water form a particular type of rock which is formed by the chemical sedimentation of limestones into gypsum and salt into various types of nitrates.
(e) During the formation of sedimentary rocks, the sediments are deposited in waterbodies and get sorted out according to their size. The sediments accumulate in different layers or strata arranged one above the other. Each layer or stratum has particles of given size. In sedimentary rocks each layer or stratum has particles of a given size. Therefore, sedimentary rocks are also called stratified rocks.

Question 3.

(a) What is meant by the term ‘metamorphism’ ?
(b) Distinguish between Thermal metamorphism and Dynamic metamorphism.
(c) Distinguish between Regional and Contact metamorphism.
(d) What are metamorphic rocks ?
(e) Give some examples of metamorphic rocks formed from sedimentary and igneous rocks.

Answer:
(a) The term metamorphism means change of form. It may be physical or chemical or both.
(b) Thermal metamorphism : When the transformation of the original rock takes place principally because of the influence of high temperature, the rock is said to be caused through Thermal metamorphism. For example, graphite (from coal) and slate (from clay). The heat may result from the intrusion of hot magma or from the friction of moving rock layers. It may also occur due to chemical changes.
Dynamic metamorphism : When the transformation of the original rock takes place mainly because of the influence of pressure at a great depth within the earth’s crust, it is known as Dynamic Metamorphism.
(c) Regional metamorphism When metamorphism of bed rocks takes place over a very large area, it is called Regional metamorphism. It is usually caused by the movement of the earth’s crust. Contact metamorphism when it takes place over a small area, it is called Local Metamorphism or Contact Metamorphism. It commonly occurs when hot magma comes in contact with other rocks.
(d) Metamorphic rocks are those rocks which were formerly igneous or sedimentary rocks, but owing to extreme heat and pressure in the interior of the earth it has been changed or altered to such an extent that they are quite different from what they once were slate, which is in reality clay, and marble’ which is in reality lime stone. Other examples of metamorphic rocks are quartzite from sand stone, graphite from coal, gneiss from granite and Mica from Schist.
(e)
(a) Sedimentary Rocks :

1. Limestone
2. Clay and Shale
3. Sandstone
4. Coal

Metamorphic Rocks :

1. Marble
2.  Slate
3. Quartzite
4. Graphite

(b)
Igneous Rocks :

1. Granite
2. Basalt

Mctamorphic Rocks :

1. Gneiss
2. Schist

Question 4.
Classify the following rocks into sedimentary, igneous and metamorphic

Answer:

(a) Shale — Sedimentary rock
(b) Gneiss — Metamorphic rock
(c) Quartzite — Metamorphic rock
(d) Slate — Metamorphic rock
(e) Marble — Metamorphic rock
(f) Coal — Sedimentary rock
(g) Clay — Sedimentary rock
(h) Schist — Metamorphic rock
(i) Granite — Igneous rock
(j) Graphite — Metamorphic rock
(k) Dolomite — Sedimentary rock
(l) Peat — Sedimentary rock
(m) Basalt — Igneous rock
(n) Rock salt — Sedimentary rock
(o) Lime-stone — Sedimentary rock
(p) Gypsum — Sedimentary rock
(q) Loess — Sedimentary rock

Question 5.
Give one word for the following

(a) The outer layer of the earth.
(b) The lower part of ocean floor, comprising mainly of silica.
(c) Rocks formed by the cooling and solidification of molten rock from beneath the earth crust.
(d) Stratified rock formed organically but from vegetative matter-swamps and forests.
(e) The upper part of lithosphere, which is rich in silica and aluminium.
(f) The core of the earth occupied by rock in iron and nickel.
(g) Igneous rocks, which contain a high percentage of silica.
(h) Igneous rocks, which contain a low percentage of silica.
(i) A sedimentary rock, which is composed of microscopically fine, soft and smooth particles.
(j) The best example of chemically-formed sedimentary rock, which has been formed by the evaporation of water from solution containing minerals.

Answer:

(a) Crust
(b) SIMA
(c) Igneous rocks
(d) Carbonaceous rocks
(e) SIAL
(f) Nife
(g) Acidic igneous rocks
(h) Basic igneous rocks
(i) Clay
(j) Gypsum

Q. 6. Fill in the blanks

1. The interior layer is the core, which is made up mainly of iron and nickel, and is called Nife.
   
2. Organically formed sedimentary rocks are formed by the deposition of shells and skeletons of organism.
3. Breccia rock is formed, when the angular and coarse grains of some durable minerals are cemented together.
4. Aeolian is the best example of the wind deposited stratified rock.
5. Basic igneous rock contain a low percentage of silica and a high percentage of basic oxides.
6. Extrusive rocks are also known as volcanic rocks.
7. Basaltic lava rocks cover wide area in Peninsular India and Columbia, the Snake Plateau of the U.S.A.

Question 7.
Give one example of an area of :

1. Igneous rocks
2. Metamorphic rocks,
3. Sedimentary rocks in India

Answer:

1. Deccan Plateau
2. Narmada Basin
3. Himalayan Region

Question 8.
What is the basis for the classification of rocks ?
Answer:
The basis for the classification of rocks are their mineral composition, colour and texture.

Question 9.
Why are Sedimentary rocks called the Secondary rocks?
Answer:
Sedimentary rocks are called Secondary rocks or derived – rocks because they are derived by the denudation of other rocks.

Question 10.
How are sedimentary rocks classified ?
Answer:
Sedimentary rocks are classified into the following types according to the nature of sediments, their origin, composition and the mode of formation.

1. Inorganic rocks or Mechanically-formed Sedimentary Rocks :- These type of rocks are formed by the deposition of land derived material. When the river began to flow, they eroded the rocks and washed away to the sea. Clay, shale, sandstone were formed in this way. These rocks are called inorganic rocks.
2. Organically formed Sedimentary Rocks :- These rocks are formed by the deposition of plants and sea organisms. Millions of years ago, there grew huge forest in marshy places. In course of ages they were buried underground and the internal heat changed them into coal. Moreover, there are millions and millions of sea-organisms whose skeleton are made of Calcium carbonate derived from sea water. After their death skeleton sink to the bottom of the seas and are formed into lime true and chalk and coal.
3. Chemically-formed Sedimentary Rocks :- There rocks are formed by the evaporation of water from solution containing mineral. Various kinds of salts precipitate from waters of shallow desert lakes, where evaporation of the water is rapid. Gypsum is the best example of this kind of rocks. Several nitrates and potash are also chemically formed sedimentary rocks.

Question 11.
State the properties of metamorphic rocks.
Answer:
Properties of metamorphic rocks :

1. These rocks are harder and more resistant than the original rocks.
2. These rocks have their minerals arranged in a series of bands.

Question 12.
Give one term for the following statements :

1. Formed when mud layers compacted under great pressure composing 80% of this rock.
2. It has a definite chemical composition with its own chemical and physical properties.
3. Igneous rocks of deep seated origin.
4. Sheet like body of igneous rock.
5. Rounded or sub-rounded fragments, usually water-born cobbles, pebble and gravel, cemented together by a matrix of calcium carbonate, silica, etc.
6. Formed by evaporation in saline lakes.
7. Fine grained metamorphic rock, generally produced by the low grade metamorphism of shale.
8. Type of metamorphism in which changes are caused due to high pressure.

Answer:

1. Shale
2. Mineral
3. Plutonic rocks
4. Sill
5. Conglomerate
6. Rock salt
7. Slate
8. Dynamic metamorphism.

Question 13.
Why are the Igneous Rocks called Primary Rocks ?
Answer:
It is believed that the earth was in a molten state in the beginning Igneous rocks were the first rocks to be formed due to cooling and solidification of molten matter. Hence these are called Primary Rocks.

Question 14.
Why fossils are preserved in Sedimentary and not in Igneous rocks ?
Answer:
Fossils are remains of vegetation and animals buried under the sediments. The sedimentary rocks are stratified rocks and are found in layers. These fossils are preserved in between these layers. But in Igneous rocks, the fossils are destroyed due to high temperature of lava.

Question 15.
How is Plutonic rock formed ? Give an example of an Plutonic rock.
Answer:
Plutonic rocks are the igneous rocks which are formed as some depth in the earth’s crust, when a molten material gets solidified under pressure. Granite is very good example of a Plutonic rock.

Question 16.
Give reasons for the following :

1. Extrusive rocks generally have small crystals.
2. Silicates are the most common rock forming minerals.
3. Rocks are of great economic significance.
4. Man’s habitat is the biosphere and not the lithosphere in the true sense.

Answer:

1. Extrusive rocks generally have small crystals because in the formation of these rocks, the solidification of magma takes place at a slower rate.
2. Silicates are the most common rock forming minerals because they are most common minerals in the Earth’s crust.
3. Rocks are of great economic significance Some of the main benefits of rocks are as follows :
   • After disintergration, they turn into valuable soils.
   • They are the store-houses of a large number of minerals.
   • They are the source of precious metals like gold, silver, platinum etc.
   • They are source of fuel-minerals.
   • They provide different types of stones.
4. The composite zone inhabited by most living creatures is called biosphere. It includes a part of the atmosphere, the hydrosphere and a part of the lithosphere. All three layers are essential for life to exist.
   As lithosphere is only a small part of the biosphere, therefore, man’s habitat is the biosphere and not the lithosphere in the true sense.

Question 17.
Distinguish between Intrusive and Extrusive Rocks :
Answer:
Intrusive Rocks :

1. Intrustive rocks are formed beneath the surface of the Earth.
2. These rocks have large size crystals due to slow cooling.
3. These are also known as plutonic rocks.
4. Granite is an example of these rocks.

Extrusive Rocks :

1. Extrusive rocks are formed on the surface of the Earth.
2. Crystals are not formed due to rapid cooling of lava.
3. These are also known as volcanic rocks.
4. Basalt is an example of these rocks.

ICSE Solutions for Class 9 Geography – Landforms of the Earth

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Exercises

I. Short answer questions.

Question 1.
What is meant by a landform ?
Answer:
A landform is a natural feature on the surface of the earth with a particular shape.

Question 2.
Why are the fold mountains called so ?
Answer:
Fold mountains are called so because of the result of large- scale earth movements caused by stresses in the earth’s crust. Such stresses may be caused by weight of the overlying rocks, movements in the mantle, the expansion or contraction of some part of the earth, etc. These stresses subject the rocks to compressive forces, producing wrinkling or folding along the lines of weakness. This is shown in fig. the raising of folds makes the fold mountains.

Question 3.
Give two chief characteristics of the fold mountains.
Answer:

1. The fold mountain system has parallel ranges.
2. A fold mountain region is also a region of sudden forces such as of volcanoes and earthquakes.

Question 4.
Give one example of each :

(a) Young fold mountains;
(b) Old fold mountain. Why they are called so

Answer:

(a) These mountains are made of light sedimentary rocks of recent tertiary age and are the highest mountain system which are still increasing their heights due to gradual upthrust force. The Himalayas are called young fold mountains.
(b) The Alpine-Himalayan system and Circum Parific mountain belt are the ‘Old Fold Mountains’ which existed as geosynclines 50-60 million years ago.

Question 5.
Give example of residual mountains.
Answer:
Examples of Residual mountains are Nilgiri, Parasnath and Rajmahal Hills in India and the Catskill range in the USA.

Question 6.
How is a rift valley formed ? Give one example of a rift valley.
Answer:
A rift valley is formed by the submergence of a big landmass between two high block mountains, e.g. the Rhine river flows through a rift valley in its middle course.

Question 7.
Give a brief definition of a plateau.
Answer:
The Himalayas are an important form of folding being the highest mountain range in the world.

Question 8.
Give one example of each :

(a) Intermontane plateau
(b) Volcanic plateau and
(c) Piedmont plateau

Answer:

(a) The Tibetan plateau
(b) The Plateau of Peninsular India.
(c) The Patagonian plateau of South America.

Question 9.
Give two points of importance of landforms.
Answer:
Various landforms display the internal and external forces of the earth, different climatic effects and features, forests, snow lands giving birth to rivers, coasts and islands as fishing regions. All these together make the earth beautiful and ideal for living and various activities.

Question 10.
What are known as epeirogenic movements ?
Answer:
The movements such as uplift and submergence working in vertical direction are known as epeirogenic movements. ‘Epeiros’ in Greek means continent ‘genic’ means building. As this movement created continents coming out higher from the oceans.

Question 11.
Name two landforms created by epeirogenic movements.
Answer:

1. Block mountains.
2. Rift valleys and basins are produced by epeirogenic movements.

Question 12.
Why are the sudden forces described as ‘Constructive forces ?
Answer:
Earthquakes and volcanic activities are described as sudden forces. These forces are described as ‘Constructive Forces’ because they create relief features on the surface of the earth. As volcanic erruptions result in the formation of volcanic mountains, extensive plateaus and also plains.

Question 13.
What are called endogenic forces ?
Answer:
Endogenic forces are the internal diastrophic forces working inside the interior of the earth related to the tectonic forces.

Question 14.
Name four relief features on the surface of the earth.
Answer:
The four major landforms are mountains, plateaus, plains, valleys and basins.

Question 15.
What are known as exogenic forces ?
Answer:
Exogenic forces work on the surface of the earth through water, wind and ice, resulting in changing the shape of landforms slowly.

Question 16.
Name the two land forms produced by exogenic forces.
Answer:

1. Alluvial and erosional plains
2. Glacial landforms.

Question 17.
Give one chief characteristic of the fold mountains.
Answer:
The fold mountains are formed by the lateral compression of sedimentary rocks as seen by the different layers of various types of rocks one upon another.

Question 18.
Give one example of volcanic mountains.
Answer:
Volcanic mountains are formed by erupting magma from the inner core on the surface e.g. Mt. Krakatoa is an active volcano on the western side of Java.

Question 19.
How is a rift valley formed ? Give one example.
Answer:
A rift valley is formed by the submergence of a big landmass between two high block mountains, e.g. the Rhine river flows through a rift valley in its middle course.

Question 20.
Give a brief definition of a plateau.
Answer:
A plateau is a higher tableland between mountain and valley, lower than mountain and higher than valley.

Question 21.
Give one example of each

(a) Intermontane plateau
(b) Piedmont plateau
(c) Volcanic plateau.

Answer:

(a) The Tibetan plateau.
(b) The Patagonian plateau of South America.
(c) The Plateau of Peninsular India.

Question 22.
How are erosional plains formed ?
Answer:
Erosional plains are formed by the agents of erosion in millions of years, when the higher landforms are eroded into level plain areas, e.g. Lorraine plain in France.

Question 23.
Give two points of importance of landforms.
Answer:
Various landforms display the internal and external forces of the earth, different climatic effects and features, forests, snow lands giving birth to rivers, coasts and islands as fishing regions. All these together make the earth beautiful and ideal for living and various activities.

II. Distinguish between each of the following 

1. Fold Mountain and Block Mountain.
2. Intermontane plateau and Volcanic plateau.
3. Structural plain and Depositional plains.
4. Tectonic mountain and Volcanic mountain.

Answer:

1. Fold Mountain :

1. Fold mountains is built by the tectonic forces folding the sedimentary rocks.
2. These are formed of light sedimentary rocks e.g. the Himalayas

Block Mountain :

1. Block mountain is built after the submergence of a landmass leaving behind the big blocks on the both sides.
2. These are formed by solid rocks standing on the both sides of a rift valley. e.g. Vosges mountain in France.

2. Intermontane plateau : These are the highest and most extensive types on the globe surrounded by hills and mountains. The plateau of Tibet is the highest plateau as well as most extensive intermontane plateau. Other examples are Columbian Plateau, North Americal Cordillera, Bolivian, Peruvian and Mexican plateaus.
Volcanic Plateau : In places where fissure eruptions have taken place magma erupts quietly through narrow fissures several kilometres in length. This magma spreads on the surface and cools down as a sheet of lava covering the surface of the land. Eruptions at intervals lead to the piling up of lava sheets one over the other in a series of steps. The Deccan trap region of Peninsular India has several lava sheets having a maximum thickness of about 200 metres. This region forms a lava plateau. Other examples are South African plateau, Columbian Plateau and Ethiopian plateau.
3. Structural plain : It is formed by the uplift of landmass by Diastrophic forces creating an extensive lowland. The Missouri – Mississippi plain of U.S.A. is an example, which came out of ocean by uplift force.
Depositional plains : These plains are formed by the deposition of materials which have been brought by various agents of transportation, eg.

1. River Deposition : The most widespread of these are alluvial plains like the Northern Plains of India; the flood plains like the Mississippi Plains in the USA, deltaic plains in Egypt and India
2. Wind Deposition : Most of such plains are sandy deserts like the Sahara in Africa and the Thar desert in India. They have irregular and undulating surface made by existence of sand dunes and hallows.
3. Marine Deposition : These plains are found in coastal regions. Examples are the east coast of India, the estuarine banks in the Netherlands, coast of Germany and Denmark.

4. Tectonic mountain :

1. It is built by the tectonic force working on the crust of the earth.
2. It is the result of upthrust force of the tectonic movement.
3. It may be built by sedimentary or metamorphic rocks.

Volcanic mountain :

1. It is built by the volcanic eruption from the interior of the earth.
2. It is the result of upthrust force of magma coming up on the earth surface.
3. It may be built by crystalline igneous rocks of particular composition.

III. Give one technical term for each of the following 

Question 1.
Block mountains with flattened summits.
Answer:
Horst Mountains.

Question 2.
Plateaus surrounded by hills and mountains on all sides.
Answer:
Intermontane plateaus.

Question 3.
Plateaus formed by lava.
Answer:
Volconic plateaus.

Question 4.
An extensive area of lowland with a level or gently undulating surface.
Answer:
Plain.

Question 5.
The compressional forces that cause folding of rocks and formation of fold mountains.
Answer:
Diastrophic forces.

Question 6.
The vertical movements which are the result of faults and cracks in the surface of the earth.
Answer:
Epeirogenic forces.

Question 7.
The forces operating on the surface of the earth.
Answer:
Exogenic forces.

Question 8.
Plateaus surrounded by mountains on one side and plains on the other.
Answer:
Piedmont plateaus

P Q. Fill in the blanks with suitable words.

1. Volcanic activity is a sudden movement.
2. The upfolds of the rock strata are called anticlines.
3. The Mid-Atlantic Ridge rises 3 km above the floor of the Atlantic.
4. The Great Plain of the USA was formed by Diastrophic forces.
5. The Great Northern plains of India were formed by River Deposition.

IV. Long Answer Questions.

Question 1.
1. Describe the formation of mountains and their types.
Answer:
Mountains are classified into three main types depending on the forces that have formed them. Three main types of mountains are

1. Fold Mountains : Fold mountains are the result of large-scale earth movements caused by stresses in the earth’s crust. Such stresses may be caused by weight of the overlying rocks, movements in the mantle, the expansion or contraction of some part of the earth, etc. These stresses subject the rocks to compressive forces, producing wrinkling or folding along the lines of weakness. This is shown in fig. The raising of folds makes the fold mountains.
   
2. Residual Mountains : Mountains which are subjected to weathering and erosion for a longtime, are lowered down and called residual or relict mountains.
   Denudation and erosion by natural agents like winds, water, snow etc., cause the mountains to be lowered but some resistant areas may remain and form residual mountains.
   They may also be formed on plateaus that are dissected by rivers. For example the hills and valleys in the Deccan plateau.
   Some examples of Residual mountains are Nilgiri, Parasnath and Rajmahal Hills in India and the Catskill range in the USA.
   
3. Block Mountains : Horst or a block mountain is an uplifted land mass situated between two adjacent faults. The central block is upthrown or land on the outer-sides of the faults is downthrown so that the central mass appears like a highland. Its surface is like a plateau, but it has steep edges. The Vosges mountains to the west of the Rhine Rift Valley and the Black Forest mountain to the east of the Rhine Rift Valley are good examples of Horsts.
   

Question 2.
Describe the characteristics of four different types of plateaus.
Answer:
Intermontane plateaus are the highest plateaus between highest mountains, e.g. Tibetan plateau. Piedmont plateaus lie between mountains and plains with steep slopes towards plains due to the force of flowing water downwards, e.g. Appolochian plateau of U.S.A., Patagonia plateau of South America Volcanic plateaus are created by volcanic eruption and Lava flows, e.g. Deccan plateau of peninsular India Uplifted plateaus are caused by the endogenic forces resulting in the dome shaped plateaus e. g. Chhotanagpur plateau in India

Question 3.
Describe the characteristics of structural plains.
Answer:
Structural plains are created by uplifting of a large landmass due to Diastrophic movements, e.g. plainofU.S.A. Erosionalplains are formed by eroding highlands into plain areas, e.g. Lorraine plain in France. Srinagar Valley of Kashmir is the result of glacial erosion, Sahara desert plain is the result of wind erosion. Karst plains are created by erosion of limestone rocks by ground water, e.g. Karst plain of Yugoslavia. Depositional plains are caused by large scale deposition of debris and silt deposited by the running water or rivers, e.g. Northern plain of India.

Question 4.
Explain the chief characteristics of depositional plains and their types.
Answer:
Depositional plains These plains are formed by the deposition of materials which have been brought by various agents of transportation, eg.

1. River Deposition : The most widespread of these are alluvial plains like the Northern Plains of India; the flood plains like the Mississippi Plains in the USA, deltaic plains in Egypt and India
2. Wind Deposition : Most such plains are sandy deserts like the Sahara in Africa and the Thar desert in India. They have irregular and undulating surface made by existence of sand dimes and hallows.
3. Marine Deposition : These plains are found in coastal regions. Examples are the east coast of India, the estuarine banks in the Netherlands, coast of Germany and Denmark.

Question 5.
Give a brief account of importance of landforms on the surface of the earth.
Answer:
Landforms play an important role for human activities by providing different aspects of landscapes, climatic variety, natural gifts of snowclad ranges, glaciers and rivers etc., various vegetation zones imparting innumerable forest’ products, agriculture and other occupations related to different types of landforms, natural beauty and tourism all these making this earth fascinating living world.

Practice Questions (Solved)

Question 1.
Describe the direction in which the following mountain systems lie and also point out the continents where they are found.

(a) Alpine Himalayan System
(b) Rocky-Andean System

Answer:

(a) Alpine and Himalayan System both run from West to East direction in Europe and Asia continents respectively.
(b) Rocky-Andean System both run from North to South in the western margins of North America and South America continents.

Question 2.
Describe the different stages in the growth of mountains.
Answer:
There are three different stages in the growth of mountains.

1. The geosyncline stage : The deposition of sediments in the sea-bed to form large geosynclines.
2. The Orogenic stage : The tectonic forces working horizontally push and press there geosynclines to form various folds.
3. Epeirogenic stage : When the whole mass of geosynclines is raised and buckled up and form a distinct series of troughs (synclines) and arcs (auticlines) i.e. Mountains and Valleys.

Question 3.
What are the different types of Geosynclines ?
Answer:
There are three types of Geosynclines

1. Monogeosynclines : Long, narrow geosynclines along narrow water bodies take the shape of narrow mountains such as Appalachian mountains of North America.
2. Polygeosynclines : Geosynclines laid down in wide and long water basin take the shape of broad and long mountain ranges like Rockies in North America.
3. Mesogeosynclines : The geosynclines lying between Europe and Africa continents resulted in various mountain ranges e.g. Alps and Pyrenees in Europe, Atlas in Africa.

Question 4.
Write a note on the characteristics of folded mountains.
Answer:
Folded mountains are formed by the forces of compression and contortion resulting in a series of synclines and anticlines, later on undergoing various erosive forces. All the highest mountain systems are example of folded mountains made of sedimentary rocks.

Question 5.
What are Block mountains ? How are they formed ?
Answer:
Block mountains are formed on the both sides of a rift valley, which is formed by deep submergence of a large landmass leaving behind two raised platform type blocks known as Block mountains. These landforms are created by displacement of landmass along fault lines known as faulting.

Question 6.
How can mountains be classified according to their different size and arrangement ? Describe in detail two of the classes of such mountains.
Answer:
Simply the mountains can be divided into 4 groups

1. Folded mountains
2. Block mountains
3. Volcanic mountains
4. Relict mountains

Volcanic mountains : are formed by the eruption and deposition of magma from the interior core to the land surface. According to their construction these are Cinder or Ash cones, Lava cones and composite cones, e.g. Fujiyama in Japan.
Relict mountains : These are formed by the continuous erosion ofthe original materials and giving birth to the hills of rounded peaks made of high density rocks, which have undergone excessive pressure and denudation by natural agents. One of the best example is Vindhyanchal mountain.

Question 7.
What are Block mountains ? How are they formed ?
Answer:
Horst or a block mountain is an uplifted land mass situated between two adjacent faults. The central block is upthrown or land on the outer-sides of the faults is downthrown so that the central mass appears like a highland. Its surface is like a plateau, but it has steep edges. The Vosges mountains to the west of the Rhine Rift Valley and the Block Forest mountains to the east of the Rhine Rift Valley are good examples of Horsts.

Question 8.
How can mountains be classified according to their different size and arrangement ?
Answer:
Mountains can be classified according to their different size and arrangement as given below :

1. CordillersThese are large regions of mountains topography which are characterised by a large number of chains and ranges.
2. System It is formed of several associated ranges. These ranges should be similar in position, form and structure although treanches or basins may separate them.
3. ChainIt is a series of ridges in one line although separated by trough like valleys.
4. RangeIt is a linear arrangement consisting of a large number of peaks and ridges separated by valleys. The different mountains possess a unity of form and structure.
5. Group It is a circular or massive arrangement of peaks and ridges. Group formations often result from the erosion of laccolths.
6. Ridge It is the individual arch or block that results from folding and faulting. It may be of various types according as the slope is steep on one side or the other.
7. Peaks These are formed by the less regular beds resisting denudation. They may be dome-like or pyramidical or needle-shaped. Their shape depends upon the rock structure and joint planes of the region. The peaks and ridges may either be arranged parallel to one another or may be quite isolated of may be arranged like features round a dome or they may be cones formed due to volcanic extrusion.

Question 9.
What are plateaus ? How are they different from mountains ? Give suitable examples.
Answer:
Plateaus Plateaus or table lands are elevated uplands, extensive in size and descending steeply to the surrounding regions. On the other hand, a portion of land surface rising considerably above the surroundings either as a single eminence or in a range if chain is called a ihountains.
Examples of Plateaus :

1. Deccan Plateau of India.
2. Tibetan Plateau (called the roof of the world)

Question 10.
What is a Piedmont Plateau ? How is it different from a Continental plateau ? Give suitable examples to illustrate.
Answer:
Piedmont Plateaus The plateaus which lie at the foot of the mountains are called Piedmont plateaus. These are flanked on one side by the plains or seas. The chief examples are the Colorado plateau or North America and the Patagonia Plateau of South America. Continental Plateaus The extensive and massive tablelands which rise abruptly from the bordering lowlands or from the sea are called continental plateaus. On most of their margins, there is sea. They seldom have mountainous rims. The major portion of Africa, Arabia, Spain, Australia, Peninsular India, Greenland and Antarctica are continental plateaus.

Question 11.
Write short notes on the following :

(a) Coastal plains
(b) Karst plains
(c) Peneplain
(d) Cuestiform plains.

Answer:

(a) Coastal plains : The plains situated near a sea coast are called coastal plains. They are formed by the sea waves after sea bottoms have emerged. The newly emerged plain is generally broad and wide and comprise of loosely compacted layers of mud and sand. Many coastal plains increased in which towards the sea because the sea waves continue adding matter to it.
(b) Karst plains : These plains are formed by the action of underground water, dissolving the regions made of chalk or limestone are called Karst plains. They are often flat-bottomed. Due to wind erosion and differential weathering, the topography is etched and rounded or even polished in a curious manner. Some of the relief features are quite fantastic in shape, especially the pebbles and other fragments that litter the surface of these plains.
(c) Peneplains : Very low undulating plains are called peneplains. They are almost plains.
(d) Cuestiform plains : The plains marked by a concentric arrangement of ridges and lowlands are called Cuestiform plains. Paris and London are the typical examples of such plains. They are made by river action on hard and soft rocks. Consequently they become rolling like the downs of S.E. England.

Question 12.
Why and how are the plains the centres of all human activity ?
Answer:
The plains are the centres of great economic advancement. The alluvial plains have been the cradles of civilisation from the earliest time. They have the following advantages to man:

1. Railways, roads and waterways can be easily laid.
2. They are the granary of the world.
3. Due to fine climate, fertile soil and facilities for movement, the plains have become thickly populated and most of the big cities and towns are situated in the plains of the world except in areas which suffer from harsh climate and temperature.

Question 13.
Differentiate between Young fold mountains and Old fold mountains.
Answer:
Old fold mountains : The fold mountains which were formed about more than 250 million years ago are called old fold mountains. For example, the Urals in Russia, the Appalachians in North America and the Aravalli range in India are old fold mountains. These mountain ranges are of low altitude and have gentle slopes.
Young fold mountains : The most recent phase of mountain building took place about 25 million years ago. The world’s highest mountain ranges were formed during this period. These are known as young fold mountains. They have rugged relief features because they have been subjected to denudation for a comparatively short period only.

Question 14.
Give reasons for the following :

1. Old fold mountains have low altitude and gentle slopes.
2. Young fold mountains have rugged relief features.
3. Young fold mountains are liable to Earthquakes and Volcanic action.

Answer:

1. Old fold mountains have low altitude and gentle slopes because they have been subjected to denudations for million of years.
2. Young fold mountains have rugged relief features because they have been subjected to denudation for a comparatively short period only.
3. Young fold mountains are liable to Earthquakes and volcanic action because these mountain regions are areas of crustal instability.

Question 15.
State two evidences that the Earth movements have taken place in the past.
Answer:
The evidences that the Earth movements have taken place in the past are as follows :

1. The basins containing sedimentary rocks indicate that such basins must have been below sea level in the past. The coalfields of the Damodar valley occur in such basins of the geological past.
2. Oilfields occur in basins containing old sedimentary rocks. Such basins are now occurring on the land. This shows that the portion of the crust which was once depressed must have been uplifted later.
3. llie Himalayas provide another evidence of the recent effect of Earth movements.

Question 16.
What causes Orogenic movemeiits ?
Answer:
Orogenic movements are caused by compressional or tensional forces.

Question 17.
What are the effects of Epeirogenic movements ?
Answer:
Effects of epeirogenic movements :

1. They cause rising or sinking of the crust. They may cause the elevation of broad areas as extensive as those of a continent or lowering of the sea level.
2. These movements are responsible for the formation of plateaux.

ICSE Solutions for Class 9 Geography – Earth’s Structure

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Exercises

I. Short Answer Questions

Question 1.
Name the sources of information about forces operating inside the earth.
Answer:
Information about forces operating inside the earth is taken by the study of seismic waves, materials thrown up by volcanoes and the evidence from the theories of the origin of the earth.

Question 2.
In which part of the earth is NIFE found ? What it is composed of ?
Answer:
NIFE is found in the inner core of die earth. NIFE is composed of Nickel (Ni) and Iron (Fe), being heavy metals and having high density, these are found deep inside the earth.

Question 3.
What are the consequences of the pressure and temperature in the interior of the earth ?
Answer:
Due to the extreme temperature of 2200° C, every matter is in liquid and gaseous state in the interior core, the temperature in the mantle ranges from 870° C to 2200° C, so things are in semi – liquid to liquid state, the crust, a layer of 60 km, breadth, is made of solid rocks with a density of 2 – 3, g/Cm³. The density goes on increasing to 3-4g/Cm³ in the mantle and 10-13 g/Cm³ in the core.

Question 4.
What is the lithosphere ?
Answer:
The crust is called Lithosphere made of solid rocks with a thickness of 60 km. below high mountains and 6-12 km below the oceans.

Question 5.
Name the three layers of the earth’s interior.
Answer:
The three layers of earth’s interior are:

1. Core
2. Mantle
3. Crust

Question 6.
State two chief characteristics of the earth’s crust.
Answer:
The crust is made of solid rocks and divided into oceans and continents.

Question 7.
Describe the mantle. State its two chief characteristics.
Answer:
Mantle lies between 60 – 2900 km. depth. It is divided into two parts namely upper mantle and lower mantle, which are in the form of solid rocks and semi-molten rocks respectively.

Question 8.
Where is asthenosphere found ? In which form does it exist ?
Answer:
At the depth of 100 – 250 km. The mantle is partially molten and known as asthenosphere, with a temperature of 1100°C.

Question 9.
Write one difference between Moho Discontinuity and Gutenberg Discontinuity.
Answer:
Moho Discontinuity is the boundary between crust and mantle and Gutenberg Discontinuity is the boundary between mantle and core.

Question 10.
Why is the earth’s interior in most part found in a solid state despite great heat and pressure ?
Answer:
The solid state of the inner core is due to high density and pressure which have compressed molten rock material and keep this layer firm and solid in some parts due to high pressure inspite of the temperature of 5000°C.

Question 11.
Name two types of earth movements.
Answer:
Two types of movements are due to isostasy and tectonic plates. Isostasy is the process of natural balance between different landforms and the sliding movement of the tectonic plates of the earth’s crust.

Question 12.
What is Geology ?
Answer:
Geology is the science dealing with the origin and types of rocks found in the interior of the earth.

II. Give reasons for each of the following

Question 1.
The study of meteorites helps scientists to know about the interior of the earth.
Answer:
At the time of the origin of the earth every planet and meteorites were floating in the space and the materials of the earth were same as that of the meteorites. So, the scientists can calculate the composition of rocks ofthe earth by studying the materials found in the meteorites.

Question 2.
Temperature starts rising gradually towards the interior of the earth.
Answer:
Due to enhancing density and pressure the temperature goes on increasing gradually towards inside of the interior of the earth.

Question 3.
The asthenosphere is in a semi-molten state.
Answer:
At the depth of 100 – 250 km the mantle is partially molten and known as asthenosphere due to the temperature around 1100°C along with greater pressure and density.

Question 4.
The inner core is in a solid state.
Answer:
The high pressure in the interior core keeps this layer firm and solid in some parts, in spite of the temperature as high as 5000°C.

Question 5.
The continents are placed above the oceans.
Answer:
The density of continents is lesser than the layer supporting the ocean beds, so the continents came floating upwards at the time of the formation and solidification of the earth, as the lighter things come upwards floating over the heavier things i. e. Sial is lighter than Sima

III. Long Answer Questions

Question 1.
Look at the figure on the side and answer the questions:

(a) Label the parts : (1), (2), (3), (4) and (5).
(b) Name the state (solid, liquid or gas) in which each part exists.

Answer:
(a)

1. Atmosphere
2. Lithosphere
3. Mantle
4. Core
5. Hydrosphere.

(b)

1. Atmosphere — Gas
2. Lithosphere — Solid
3. Mantle — Semi-solid
4. Core — Molten state or liquid
5. Hydrosphere — Liquid (water)

(c) What part is suitable for human habitation? Why? Ans. Outer part of the earth is suitable for human habitation due to favourable conditions for survival, i.e. atmosphere for air, Lithosphere for settlement due to ideal temperature and land, hydrosphere for hydrological cycle for providing rainfall and fresh water bodies on the earth and oceans for navigation and trade routes etc.

Question 2.
Describe the layers of the interior of the earth and their chemical composition.
Answer:
The interior of the earth is divided into three major parts i.e. crust, mantle and core. The crust consists of majority of, silica and aluminium and is called ‘SIAL’, mantle is called SIMA due to the majority of silica and magnesium and is called SIMA, which makes the bed of oceans and the core is called NIFE with excess of Nickel and Iron (Ni + Fe).

Question 3.
There are two transitional zones between the two consecutive layers of the interior of the earth. Name them and state their chief characteristics.
Answer:
The transitional zone between crust and mantle is Moho Discontinuity which is the dividing zone between solid and semi-solid state of rocks due to the increasing temperature as the depth increases. The boundary between mantle and core is known as Gutenberg Discontinuity, below this zone both density and temperature going on increasing. The density is more than 13 and temperature is more than 2200°C.

Question 4.
Explain the layers of the interior of the earth with reference to the following :

(a) Depth,
(b) Temperature
(c) Density.

Answer:
Crust :

(a) Depth 35-50 km below continents and 6-12 km. below the oceans.
(b) Temperature — Less than 870°C
(c) Density — 2.7 g/Cm³ – 5.5 g/Cm³.

Mantle :

(a) Depth — 50 – 2900 km.
(b) Temperature — 1500° C – 2200°C
(c) Density — 3 g/Cm³ – 4.5 g/Cm³

Core :

(a) Depth — 2900 km – 3500 km
(b) Temperature — 2200°C – 5000°C
(c) Density — 10.0 g/Cm³ – 13.6 g/Cm³.

Question 5.
Study the figure on the side and answer the questions:

(a) What is known as Sial ? How deep is the area marked by Sial ?
(b) What role does Sima play ?
(c) Why is the expression ‘Nife’ so called ?
(d) Which layer is responsible for earth’s magnetic field ? Why?
(e) What happens to the continents if there is an earthquake?

Answer:

(a) Sial is the upper layer or crust of the earth. The name Sial is based on the excess of Silica and Aluminium. The depth of Sial is 60 km.
(b) Sima is the second layer of earth which gives support to the ocean beds. There is the excess of Silica and Magnesium.
(c) ‘Nife’ means Nickel (Ni) and Iron (Fe) due to the majority of Nickel and Iron in the core,
(d) Core of earth is responsible for earth’s magnetic field because it is composed of iron and nickel which is responsible for earth’s magnetism. Magnetic field is oriented towards North and South Poles.
(e) Several drastic changes may occur during the earthquake. It depends on the intensity of the earthquake. If intensity is 8 or more buildings may break up, casualties and major changes on the landforms as broad breaking gaps, origin or disappearing of several small islands.

Practice Questions (Solved)

Question 1.
Which are the two most abundant chemical elements in the Earth’s crust ?
Answer:
Oxygen and Silicon.

Question 2.
Why does the Sun not rise at the same time everywhere in the world ?
Answer:
If the Earth were flat, the whole world would have the sunrise and sunset at the same time. As the Earth is spherical and rotates from West to East, places in the East see the Sun earlier than the places in the West.

Question 3.
“The whole of the approaching ship is not visible at one time.” Why ?
Answer:
The Earth has a spherical snape. Along its curved surface, the appearance of a ship is gradual. We see first the smoke, then the mast and then the hull. If the Earth were flat, the entire ship would be seen all at once.

Question 4.
“Even when the Earth is spherical, it appears to be flat.” Discuss.
Answer:
The actual shape of the Earth is spherical. The curvature of the Earth is small as compared to its big size. For a small area upto 100 sq. miles, this curvature is negligible. Therefore, it appears flat.

Question 5.
Why is the Earth slightly flattened at the poles ?
Answer:
The Earth is not a perfect sphere. It is slightly flattened at both the poles. It is due to the centripetal force produced by the rotation of the Earth.

Question 6.
Explain briefly the structure of the earth.
OR
Discuss the structure of the earth giving details about each of its layers and arguments in support of your contention.
Answer:
The structure of the earth means the interior of the earth.
The entire earth is composed of three zones

1. Lithosphere
2. Mesosphere and
3. Barysphere.

(i) The Crust or Lithosphere It is the outermost layer. Its thickness varies from 8 to 60 kms. It is solid and is formed largely of igneous rocks. The crust consists of two layers.

1. a lower, continuous layer of basaltic (mafic) rocks and
2. and upper layer of granitic (felsic) rock, which constitutes bulk of continents. It is absent in ocean basins. These parts of the crust forming the continents are much thicker than the crust under the oceans. Its main universal constituents are Silica and Aluminium. It is collectively known as ‘SIAL’. It has an average density of 2.7. The lower layer has an average density of 3.0. It main mineral constituents are Silica (SI) and Magnesium (MA) and is therefore called ‘SIMA’. Since the SIAL is lighter than the SIMA, the continents can be said to be floating on the layer of denser SIMA.

(ii) Mantle or The Mesosphere Beneath the crust or Lithosphere lies the Mantle or Mesosphere. Its thickness is 2840 km. Its density is 3.1 to 5.0. It depth is 2900 km. It is again divided into two sub layers.

1. the internal Silicate layer (SIMA). Its thickness is 1140 km and density varies from 3.1 to 4.75 and
2. Mixed layer of metals and silicates. Its thickness is 1700 kms. and density is 4.75 – 5.0.

(iii) Core or the Barysphere It is the central nucleus. It is made up of dense rock materials – Nickel and Iron. It is also called the layer ‘NIFE’. Its thickness is 3471 km (radius of core). It is again divided into two sub-layer

1. The outer core is liquid or plastic in nature and
2. Inner core (Barysphere) which is solid and rigid because of tremendous overlying pressure. The density of core is 5.1 to 13.

Question 7.
Where is Mantle located in the Earth ?
Answer:
The Mantle or Mesosphere is located between 2850 – 2900 km beneath the earth crust.

Question 8.
Describe any three experiments to prove the Spherical Shape of the Earth.
Answer:

1. If you observe a ship approaching sea coast, the top of the mast is seen first and the hull, lower parts are seen gradually. Due to the curvature of the Earth, the whole ship is not seen at one time.
   
2. Fix three poles of equal length at equal distance on the ground. These do not give a horizontal level. The top of the middle pole looks higher than the other two poles due to the curvature pf the Earth. This experiment was done by Mr A.R. Wallace on Bedford canal.
   
3. If you look around at the Earth’s horizon (where Earth and sky appear to meet), it will everywhere and always appear circular. It widens with increasing altitude due to Spherical Earth.
   

ICSE Solutions for Class 9 Geography – Rotation and Revolution

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Exercises

I. Short Answer Questions.

Question 1.
What is meant by the earth’s axis ?
Answer:
The earth’s axis is the imaginary line joining the North Pole to South Pole, around which the earth rotates.

Question 2.
Name the two chief motions of the earth.
Answer:
Two chief motions of the earth are rotation and revolution.

Question 3.
Describe two characteristics of rotation.
Answer:
Two characteristics of rotation are the complete rotation of the earth from west to east in 24 hours and along its tilted axis which is always in the same direction towards the Pole Star.

Question 4.
Mention two effects of the rotation of the earth.
Answer:
Day and night are caused by the rotation and the creation of centrifugal force resulting in a bulge in the equatorial part and flattened top at the poles.

Question 5.
Mention any two possible consequences if the axis of the earth was vertical instead of inclined.
Answer:

1. Then at all places on the earth, lengths of day and night would have been equal, i.e. 12 hr of day and 12 hr of night
2. There would have been no seasons.

Question 6.
State one reason why we do not feel the motions of the earth.
Answer:
According to the gravitational force every thing is attached to the earth, keeping everything at rest at their original position, unless any external force compels to motivate it.

Question 7.
Define ‘revolution’.
Answer:
Revolution is the revolving of the earth on its orbit around the sun in 365 days and 6 hours nearly.

Question 8.
State two chief characteristics of the revolution of the earth.
Answer:
The earth revolves at an average speed of 100,000 km per hour. The earth revolves in an elliptical orbit with two particular positions i.e. perihelion 147.3 million km away from sun in January and aphelion 152 million km away from sun in July.

Question 9.
Mention two effects of revolution.
Answer:
Two main effects of revolution are the seasonal changes throughout the year and the creation of particular heat zones on temperature zones.

Question 10.
What is meant by Summer Solstice ? When do we have Summer Solstice in the Northern Hemisphere ?
Answer:
Summer Solstice occurs on June 21, in the Northern Hemisphere, when the sun is overhead at the Tropic of Cancer and the North Pole is tilted towards the sun, so the summer season is experienced in the Northern Hemisphere.

Question 11.
What is meant by Equinox ? Give the dates of the two Equinoxes.
Answer:
Equinox means the time when the days and nights are equal all over the world. The particular dates of equinoxes are 21st March (Spring or Vernal Equinox) and 23rd September (Autumnal Equinox).

Question 12.
What will be the duration of daylight in the Northern Hemisphere on March 21st at 23°30′ latitude ?
Answer:
The duration of daylight will be of 12 hours.

Question 13.
What is the relationship of seasons between the Northern and Southern Hemispheres ?
Answer:
The seasonal episodes are reciprocal with each other i.e. if Northern Hemisphere experiences summer season, then Southern Hemisphere has winter season; in the same way if . there is spring season in Northern Hemisphere, there is autumn season in Southern Hemisphere and vice-versa.

Question 14.
How has the phenomenon of the ‘Midnight Sun’ come about ?
Answer:
Beyond the Arctic Circle, the regions experience 24 hours daylight in summer season due to the North Pole facing continuously towards the pole. It is called the ‘Midnight Sun’. Norway is called land of Midnight Sun.

Question 15.
What are the seasons in the Northern and the Southern Hemispheres on 23rd September ?
Answer:
There are Autumn season and spring season in the Northern and Southern Hemispheres on 23rd September, respectively.

Question 16.
Mention one effect of seasons in low and high latitudes.
Answer:
The effect of seasons in low and high latitudes is distinct through various phases of different seasons. Low latitude areas get ample temperature and rainfall while the high latitude areas are cold and receive less rainfall. Tropical regions are always warm with heavy rainfall season, while the temperate and polar regions are cold with scanty rainfall, while the polar regions are always covered with perpetual snow due to the temperature below 0°C.

II. Give reasons for each of the following

Question 1.
We always see the sun rising in the East.
Answer:
As the earth moves from West to East, the eastern part gets lighted first and we see the sunrise in the East.

Question 2.
Norway is called the Land of the Midnight Sun.
Answer:
Northern part of Norway is beyond the Arctic Circle where the sunlight remains for she months from March to September, so it is called the Land of Midnight sun due to the sunlight seen at night, too.

Question 3.
The speed of the rotation of the earth is greater at the Equator than at the Arctic Circle.
Answer:
As every part of the earth takes a frill round within 24 hours, the equator being the largest circle of latitude 0°, the speed is greatest at the equator due to crossing the maximum distance per hour. i.e. it is 1660 km per hour, while it decreases to 0° at poles.

Question 4.
25 th of December in New Zealand may be one of the hottest days of the year.
Answer:
The sun’s rays are vertical over the Tropic of Capricorn, so . 25th December may be one of hottest days in NewZealand, being situated in the Southern Hemisphere.

Question 5.
The length of day and night is not equal at all places on the earth.
Answer:
Due to the tilted axis of the’earth and the migration belt of the sun between Tropics of Cancer and. Capricorn, the length of day and night differ from place to place and region to region.

Question 6.
The period of twilight and dawn increases polewards.
Answer:
On account of the oblique path of the sun towards poles than the vertical path along the equator, the length of dawn and twilight is greater, as it is nearly one hour near equator and 50 days at the poles.

Question 7.
Noon is hotter than morning.
Answer:
Due to the vertical rays of the sun at noon and the slanting rays in the morning, Noon is hotter than morning.

Question 8.
Days and nights are equal at all places on earth on March 21.
Answer:
The rays of the sun fall vertical on the equator or the middle part of the earth, on March 21, So the distribution of light is equal all over the world resulting the duration of the day and night equal from pole to pole. It is called the Vernal Equinox

Question 9.
Vertical rays are hotter than slanting rays.
Answer:
Vertical rays are hotter, because these cross shorter distance from the sun to the earth. Consequently the tropical belt is hotter than temperate and polar areas.

Question 10.
Though the earth is nearest to sun in winter yet the winter is cool.
Answer:
During the Winter Solstice the earth’s Southern pole is facing towards the sun and the Northern Hemisphere experiences winter season and cold inspite of the earth’s nearest position to the sun.

III. Long Answer Questions

Question 1.
What is meant by rotation of the earth ? Discuss the effect of the rotation of the earth.
Answer:

(a) Rotation of the earth takes place around the axis of the earth within 24 hours making one complete round.
(b) The rotation causes day and night alternately; the part of the earth facing the sun experiences day and on the opposite side the dark part experiences night. One night and one day together make a complete solar day.

Question 2.
Describe the two interesting phenomena made by the circle of illumination viz., Solstice and Equinox.
Answer:
Circle of illumination is the lighted part of the earth by the sun. On June 21, Northern Hemisphere enjoys the longest day due to the sun’s position overhead at the Tropic of Cancer. It is called Summer Solstice. On the other hand when the sun is overhead on the Tropic of Capricorn, the Southern Hemisphere gets the longest day on December 22, which is known as Winter Solstice. The dates of Equinox are 21st March and 23rd September, when the days and nights are equal all over the world and there are spring and autumn seasons in Northern Hemisphere and autumn and spring in Southern Hemisphere respectively.

Question 3.
What is the effect of the inclined axis of the earth on day and night ?
Answer:
The difference in the duration of days and nights all over the earth is on account of the inclined axis of the earth. There is six months day in North Pole in summer season (from April to September) and six months day in South Pole in winter season (from October to March).

Question 4.

1. On which two days are the days and nights equal all over the world and why ? What name do you give to these days ?
2. Which is the largest and which is the shortest day in the Northern Hemisphere and why ?
3. On which dates does the sun shine vertically overhead at
   (a) Equator,
   (b) Tropic of Cancer.
   (c) Tropic of Capricorn ?

Answer:

1. On 21st March and 23rd September the days and flights are equal all over and world due to the sun’s rays vertical on the equator. The name is Equinox of this position.
2. The largest day is 21st June and the shortest day is 22nd December in the Northern Hemisphere.
3. The sun is overhead on :
   (a) Equator on 21st March and 23rd September.
   (b) Tropic of Cancer on 21st June.
   (c) Tropic of Capricorn oh 22nd December.

Question 5.
Describe how the duration of sunlight changes from the Equator to the Poles with respect to the angle of incidence.
Answer:
As the angle of incidence changes from 0° to 90° from Poles towards the Equator; So the duration of sunlight also changes. Duration of daylight is 12 hours on equator and 24 hours on the North Pole in summer and 24 hours on the South Pole in winter. So the duration of sunlight increases from the Equator to the North Pole and decrease in the winter season and vice-versa in between Equator and South Pole.

Question 6.
With the help of a diagram describe the heat zones.
Answer:

Question 7.
Explain with the help of diagram how the tilt of the earth’s axis and the revolution cause

1. seasons.
2. variation in the length of day and night; and
3. changes in the altitude of the midday sun at different times of the year.

Answer:

1. On account of the different positions of the earth with respect to the sun, in its orbit, various types of seasons are caused. The sun remains vertical on Tropic of Cancer on 21st June and on Tropic of Capricorn on 22nd December and on equator on 21st March and 23rd September. Besides this, the Arctic and the Antarctic Circles, there is the sunlight for six months from March to September and from September to March respectively. The winter season from December to March, spring season from March to June, summer from June to September and Autumn from September to December in the Northern Hemisphere and vice-versa in the Southern Hemisphere.
   
2. The length of day decreases from the equator to the Poles. Apart from this the polar areas experience six month days and six months nights respectively.
3. The belt of sun’s migration lies between the Tropic of Cancer and Capricorn, consequently the sun remains overhead in this belt, while beyond this belt the sun never remains vertical at noon and the sun’s track remains slanting with shorter curved path in other regions.

Question 8.
Describe how seasons are made and reversed between the Northern and Southern Hemispheres.
Answer:
Due to the tilted axis of the earth, the Northern Hemisphere gets maximum sunlight from March to September and Southern Hemisphere from September to March. So, the seasons are also reversed e.g. the summer season in Northern Hemisphere correspond by winter in Southern Hemisphere and the spring is exchanged with Autumn season.

Question 9.
Distinguish between :

1. Rotation and Revolution
2. Vertical and Slanting Rays.
3. Equinox and Solstice.
4. Twilight and Dawn.

Answer:
(i) Rotation :

(a) It is the motion of the earth along its axis.
(b) The time taken for rotation is 24 hours.
(c) It causes days and nights.

Revolution :

(a) It is the motion of the earth on its orbit around the sun.
(b) The time taken for revolution is 365 days. It causes the different types of seasons.

(ii) Vertical Rays :

(a) Vertical Rays of the sun fall within its migration belt.
(b) Migration belts is between Tropics of Cancer and Capricorn.

Slanting Rays. :

(a) Slanting Rays of the sun fall in temperate and Polar regions.
(b) Slanting Rays of the sun fall in 23 1/21° N – 90°N and 23 1/21° s – 90°S regions

(iii) Equinox :

(a) It means the duration of days and nights equal.
(b) 21st March and 23rd September are the dates of Equinox all over the world.
(c) The sun is vertical on the equator.

Solstice :

(a) It is the particular position of the earth during the year.
(b) The dates of summer and Winter Solstices are 21st June and 22nd December.
(c) The sun is vertical on the Tropic of Cancer and Tropic of Capricorn respectively.

(iv) Twilight :

(a) It is the reflection of light of the sun after the sunset.
(b) This light is slightly yellowish in colour.

Dawn :

(a) It is the reflection of light of the sun before the sunrise.
(b) This light is slightly reddish in colour

Practice Questions (Solved)

Question 1.
Name the two movements of the Earth.
Answer:
Rotation and Revolution.

Question 2.
How much time does the Earth take for one revolution?
Answer:
365 days 5 hours 48 minutes 46 seconds.

Question 3.
State the direction of rotation of Earth.
Answer:
West to East.

Question 4.
Name the longest day in the Northern Hemisphere.
Answer:
21st June.

Question 5.
Name the shortest day in the Northern Hemisphere.
Answer:
22nd December.

Question 6.
Name the longest day in the Southern Hemisphere.
Answer:
22nd December

Question 7.
Name the shortest day in the Southern Hemisphere.
Answer:
21st June.

Question 8.
On what dates are the days and nights equal throughout the world ?
Answer:
21st March and 23rd September.

Question 9.
At which latitude, is the Sun overhead on 21st June ?
Answer:
23 1/2° North.

Question 10.
At which latitude is the Sun overhead on 22nd – December?
Answer:
23 1/2° South.

Question 11.
Name the two ends of the Axis of the Earth.
Answer:
North pole and South Pole.

Question 12.
What is the speed of rotation at the equator ?
Answer:
1600 km per hour.

Question 13.
Which country is known as the land of the ‘midnight Sun’?
Answer:
Norway.

Question 14.
Which country is known as the land of the rising Sun?
Answer:
Japan.

Question 15.
What does the word equinox mean ?
Answer:
Equal nights.

Question 16.
We always see the Sun rising in the East. Why ?
Answer:
Because the Earth rotates from West to East.

Question 17.
What the word ‘Solstice mean’?
Answer:
It means the Sun standing still.

Question 18.
When does the summer solstice occur ?
Answer:
On 21st June.

Question 19.
When does the winter solstice occur ?
Answer:
On 22nd December.

Question 20.
When is the spring equinox ?
Answer:
On 21st March.

Question 21.

(a) What do you mean by “Rotation of Earth” ?
(b) What are its effects ?

Answer:
The two motion of the earth are :

1. Rotation or the daily motion and,
2. Revolution or the annual motion.

Rotation : The earth rotates (turns) round its axis from west to east once in twenty four hours. This motion is called the Daily Motion or Rotation. This rotation of the earth is the real cause of the apparent rising and setting of the sun which is stationary.

Its effects :

1. Day and night’s are caused. This is by far the most important effect of rotation.
2. The sun, the moon and the star appear to revolve round the earth from east to west.
3. Winds and currents changes their direction.
4. Different places have different local times.
5. Tides occur regularly twice a day.

Revolution : The earth revolves round the Sun once approximately 365 – 1/4 days. This motion of the earth round the Sun is called Revolution. The earth revolves round the sun in a fixed path at a speed of 29.8 km/sec. or 107,2000 km. per hour. This path is called the orbit of the earth. The earth’s orbit round the Sun cover a distance of about 965 million km.

Its effects :

1. This motion of the earth is one of the cause of the seasons.
2. Days and nights are of unequal length at the same place.
3. Change in the altitude of midday Sun during the year.

Question 22.
Give reasons for the following statements :

(a) The Sun does not rise at the same time everywhere in the world.
(b) The speed of rotation at Leningrad (60°N), Genoa (45°N) and Singapore (0°N) along the Earth’s axis is not the same.
(c) We do not feel the great speeds of Earth’s rotation in day-to-day life.

Answer:

(a) The Sun does not rise at the same time everywhere in the world because earth is not a flat disc.
(b) The speed of rotation at Leningrad (60°N), Genoa (45°N) and Singapore (0°N) along the Earth’s axis is not the same because of the spherical shape of the earth.
(c) We do not feel the great speeds of Earth’s rotation in day- to-day life because the land, water and the air around the Earth are moving as a whole.

Question 23.
Give reasons for the following statements :

(a) The areas, lying on the Equator, have their duration of day-light almost constant throughout the year.
(b) The duration of day and night is equal everywhere on 21st March and 23rd September.
(c) Daylight decreases as we go polewards from March 21st to June 21st in the Southern Hemisphere.
(d) Beyond the tropics, the Sun is never overhead.
(e) On the 22nd of December, the altitude of the midday Sun at Colombo is different from that of Delhi.
(f) The regions, near North Pole and South Pole, have six months of continuous day-light and darkness.

Answer:

(a) Days and Night are equal throughout the year at the equator that is both days and nights are of twelve hours duration there.
Reason : The reason for this is that throughout the course of earth’s revolution round the Sun, one half of the equator is always in the light and other is in the dark, that is the circle of illumination always cut the equator into two equal parts. Hence days and nights are always equal to every point at the equator.
(b) These are two special positions in the revolutionary course of the Earth, when days and nights are equal throughout the world. They are the two equinox, the first on Margh 21 st and the second on September, 23 rd. Because on these two days the mid-day sun is overhead at the equator, the positions of both the hemispheres are the same in respect of the sun.
(c) After March 21st the sun starts it’s apparent movement towards the North and Circle of illumination cuts the latitude of southern portion unequally so that the antarctic circle comes in complete darkness till June 21st, and the major portion of other latitude lies on darker side.
(d) This happens because tilt causes each hemisphere to lean towards the sun alternately for parts of the year. It also changes the apparent altitude of the mid day Sun.
(e) On December 22 the altitude of mid-day sun decreases beyond the Tropic of Cancer (Delhi) and increases towards the Equator (Colombo).
(f) On account of the obliquity of the earth’s axis, for six month i.e., from March 21 to Sept. 23 the north pole is inclined towards the Sun and is always in the light. During this period the South pole is inclined away from the Sun and is throughout in the dark. Hence it is day for six months at the north pole and night at the south pole. But from September 23 to March 21st the case is just the opposite. The north pole is inclined away from the Sun and is in the dark while the south pole is inclined, towards the Sun and is in the light.

Question 24.
Give reasons for the following :

(a) Twilight is of longer duration in higher latitudes than at Equator.
(b) Altitude of the Sun varies at a place according to seasons.
(c) Seasons are reversed between Northern and Southern Hemisphere.
(d) The duration of day and night is equal everywhere in the world on 21st March.
(e) Tropical latitudes are the hottest part of the’Earth.
(f) The period of Twilight and Dawn increases polewards.
(g) 25th of December (Christmas) in New Zealand may be one of the hottest days of the year.
(h) Noon is hotter than morning.
(i) Vertical rays are hotter than slanting rays.
(j) There is no Twilight and Dawn on the Equator.
(k) Sun rises on the east.
(l) Norway is called the land of the Midnight Sun.
(m) The speed of the rotation of the earth is greater at the Equator than at the Arctic Circle.
(n) Winds are deflected to the right in Northern Hemisphere and to the left in Southern Hemisphere.
(o) The variation in the lengths of day and night goes on increasing polewards.

Answer:

(a) The duration of twilight at a place depends on the path of the Sun in the sky. In the low latitudes, where the Sun’s path is almost vertical, the duration of twilight is short. The Sun sinks below the horizon rapidly. In the middle and high latitudes the duration of twilight is long because at these latitudes the Sun has an inclined path.
(b) The altitude of the mid-day sun is related to the latitude of a place. Because of seasonal changes in the altitude of the sun at different latitudes, the altitude of midday sun also varies.
(c) The 23.45° tilt between the equator and the orbital plane causes each Hemisphere to lean towards the sun for part of the year. So seasons are reversed between the two Hemispheres.
(d) On March 21 rays of the sun fall vertically on the equator, and because of inclined axis of the earth, the circle of illumination passes through the two poles resulting in equal duration of day and night all over the world.
(e) Tropical latitudes are the hottest part of the Earth, because the belt between Tropic of cancer and Capricorn is the migration belt of the Sun in which the Sun remains overhead on one or another place which naturally receives the maximum heat of Sun.
(f) Latitudes go on increasing polewards. In the middle and high altitudes duration of sunlight is limited. Both twilight and dawn continue so long as the sun is 18° below the horizon. Duration of twilight and dawn is especially large beyond 50° latitude.
(g) New Zealand is located at 40° latitude. On 22 December sun is in the Southern Hemisphere (Winter Solstice). So December 25 may be one of the hottest days of the year in New Zealand.
(h) At noon sun rays fall vertically overhead covering shorter distance than the slanting rays of the morning.
(i) Vertical rays remain focussed over a shorter area than slanting rays. During slanting rays solar radiation is spread over a larger area.
(j) The Twilight and Dawn depend on the path of the sun in the sky. At the Equators, sun’s path is almost vertical. So duration of twilight and dawn combine with sunset and sunrise.
(k) Earth rotates from west to east, which makes us see sun rise from the east.
(l) The good part of Norway is situated North of the Arctic Circle where duration of daylight goes on increasing from 24 hrs to six months poleward.
(m) Earth is spherical in shape and its circumference is greater at the equator than at the Arctic Circle.
(n) Earth spins west to east in inclined position. The deflection of moving air streams, known as Coriolis Force, is produced because earth beneath moves.
(o) It is because circle of illumination is widest at the equator and goes on decreasing towards the poles.

Question 25.
What is Midnight Sun ? Where does it shine ?
Answer:
Day light increases as we go polewards. At the Arctic Circle the sun never sets at mid-summer (21st June) and sunshine is received for all the 24 hours. The areas include parts of Alaska and Northern Europe. In most parts of Norway, situated north of the Arctic Circle, Sun shines 24 hours over the beautiful country side. A place called Hammerfest has become famous as the place of Midnight Sun. In the Antarctica, surrounding the South Pole, Sun shine all night during the South Summer, late in December.

Question 26.
Why are there seasons on earth ?
Answer:
The axis of the earth is inclined at an angle of 66 1 °/2 to its orbital plane or 21 1 °/2 between equator and orbital plane. While earth swings around the Sun. Different parts of its surface are exposed to sunlight for different lengths of time each day. Some regions bask in the warmth of the sunlight while others remain cold. Earth’s tilt while spreading the light over a larger area causes changes in the altitudes of the sun in different latitudes. This causes slow changes in temperature at a place. The changing weather conditions in an annual cycle of revolution is called Season. If the earth did not tilt on its axis there would be no seasons.

Question 27.
Why are days longer than nights in summer ?
Answer:
During summer the North Pole continue to slant more towards the sun. Because of the tilt it exposes larger area to sunshine. The Northern Hemisphere in this case has longer days and shorter nights. On 22 June, North Pole slants most towards the Sun, this is the longest day (the Summer Solstice) in Northern Hemisphere. The situation is exactly opposite in Southern Hemisphere. On 22nd December is remains tilted most towards the Sun. So the days are longer and nights are shorter in the Southern Summer which is opposite of Northern Winter.

Question 28.
Nearness to Sun is normally responsible for hot- weather conditions, but in July earth is farthest from Sun when it is hot in Northern Hemisphere. Why does reverse happen ?
Answer:
Due to tilt in earths axis the Northern Hemisphere is directly exposed to Sun in July when the Sun rays strike directly. Further considering the enormous distance between sun and earth the difference between maximum and minimum distance is small, just 5 million km.

Question 29.
How is that the opposite seasons are found in Australia and India ?
Answer:
India lies in the Northern Hemisphere while Australia lies in the Southern Hemisphere. Due to inclination of the Axis of the Earth, opposite seasons occur in two Hemispheres. On 21st June, when the Northern Hemisphere is inclined towards the Sun, the Southern Hemisphere turns away from the Sun. When it is summer in India, it is winter in Australia.

Question 30.
Why are days and nights equal throughout the world on 21st March and 23rd September ?
Answer:
21 st March and 23rd September are seasonal positions of the Earth and are known as equinoxes meaning equal nights. The Sun is overhead at the equator. Both the Hemispheres are equally inclined towards the Sun. The circle of light passes through the poles. With the result, one half of each hemisphere is in the light and the other half in darkness. So the days and nights are equal all over the world.

Question 31.
Daylight increases as we go polewards in summer in The Northern Hemisphere. Why ?
Answer:
In summer, the Sun is overhead at the Tropic of Cancer (23 1 /2° N). The northern hemisphere is inclined towards the Sun. The circle of light does not pass through the poles. The circle, of light cuts all the parallels unequally. The larger part of each parallel is in light. So days are longer than nights. At 66 1 /2° N latitude, there is 24 hour complete, continuous daylight. Thus, North pole has daylight for six months

Question 32.
Account for the unequal length of day and night.
Answer:
The length of day and night varies throughout the year. Sometimes the days are longer and nights are shorter and vice versa. It is due to two reasons :

(a) The inclination of the axis.
(b) The revolution of the Earth.

Due to inclined axis, one hemisphere leans towards the Sun for the six months ; the other Hemisphere leans towards the Sun for the next six months. In summer, on 21st June, days are longer in northern Hemisphere and the nights are shorter. In winter, the conditions are reversed, the days are shorter and nights are longer in the Northern Hemisphere. If the axes were vertical, there would have been equal days and nights everywhere.

Question 33.
What are the effects of the inclination of the axis ?
Answer:

(a) There is apparent movement of the Sun from the equator towards tropics.
(b) It causes opposite seasons in the two Hemisphere.
(c) It results in the variation of length of day and night.
(d) When North Pole is tilted towards the Sun, the South Pole turns away from the Sun. So the two Hemispheres are alternately exposed to the Sun rays.

Question 34.
What are the results of the difference in the Earth’s speed of rotation at various latitudes ?
Answer:
At equator, the Earth’s speed of rotation is about 1600 km per hour. The speed, goes on decreasing poleward. At 60° latitude, it is 800 km per hour. This difference affects the general circulation of the atmosphere. Winds are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. Similarly, the ocean currents are also deflected. This is known as Ferral’s Law. Due to this, the Earth is flattened at the poles and bulging at the equator.

Question 35.
Distinguish between the following pairs :

(a) Summer Solstice and Winter Solstice.
(b) Solstice and Equinoxes

Answer:
(a)
Summer Solstice :

1. The Earth is in this position on its orbit on 21st June.
2. The Sun is overhead on Tropic of Cancer (23 1/2° N).
3. Days are longer than nights in the Northern Hemisphere.
4. There is summer season in the Northern and winter season in the Southern Hemisphere.

Winter Solstice :

1. The Earth is in this position on its orbit on 22nd December.
2. The Sun is overhead on Tropic of Capricorn (23 1/2° S).
3. Days are shorter than night in the Northern Hemisphere.
4. There is winter season in the Northern and summer season in the Southern Hemisphere.

(b)
Solstices :

1. The positions of the Earth on 21st June and 22nd December are known as Solstices.
2. The Sun is overhead at tropics.
3. Days and nights are unequal.
4. The term Solstice mean “Sun standing ‘still’.
5. There is summer or winter season in Northern Hemisphere.

Equinoxes :

1. The positions of the Earth on 23rd September and 21st March are known as Equinoxes.
2. The Sun is overhead at Equator.
3. Days and nights are equal.
4. The term Equinox means ‘Equal nights’.
5. There is autumn or spring season in Northern Hemisphere.

Question 36.

(a) Define Rotation
(b) What is the period of rotation?
(c) What are its effects ?

Answer:
Rotation : The spinning of the Earth on its axis from West to East is called rotation. The Earth takes about 24 hours (23 hours 56 minutes 4 seconds) to complete one rotation. It is also known as daily motion of the Earth.
Effects :

(a) Rotation causes days and nights.
(b) All heavenly bodies like Sun, Moon, planets appear to move from East to West.
(c) Tides occur regularly twice a day.
(d) Winds and ocean currents change their directions.
(e) The four main directions (North, South, East, West) can be determined with the help of rotation.
(f) We get a measure of time. A day consists of 24 hours – one complete rotation.
(g) The different times of a day like sunrise, noon, sunset, midnight can be determined due to rotation.

Question 37.

(a) What is revolution ?
(b) What is period of revolution ?
(c) What are aphelion and perihelion ?
(d) What are its effects ?

Answer:
Revolution : The spinning of the Earth around the sun, along an elliptical orbit from West to East is known as revolution. It takes a year or 365 1/4 days to complete one revolution. Hence, it is also known as annual motion of the Earth. The Earth’s axis is always inclined at a fixed angle of 66 1/2° to the plane of the ecliptic. When the Earth is farthest from the Sun (152 million km) it is aphelion. When the Earth is nearest the Sun (147 million km) it is perihelion.

Effects :

(a) Due to revolution, the length of days and nights vary at a place at different times of the year.
(b) Revolution causes change of seasons.
(c) It helps in the location of Tropic of Cancer and Tropic of Capricorn due to the fact that Sun rays fall vertical he’re.
(d) Altitude of the mid-day Sun changes.
(e) It gives us a measure of time for one year.
(f) Poles have days and nights of 6 months duration.
(g) It determines the distribution of solar energy on the Earth.

ICSE Solutions for Class 9 Geography – Geographic Grid: Latitudes and Longitudes

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Exercises

I. Short Answer Questions

Question 1.
What is a geographic grid ?
Answer:
The network of the latitudes and the longitudes is known as a geographical grid.

Question 2.
Who devised the lines of latitude and longitude ?
Answer:
Eratosthenes, the Greek philosopher, first time devised the lines of latitude and longitude.

Question 3.
What are lines of latitude and longitude ?
Answer:
The latitudes are the parallel circles with respect to the equator reducing in length northwards and southwards and the poles are the points only. On the other hand longitudes are equal in length drawn from North Pole to South Pole with their intervals reducing towards poles.

Question 4.
Mention two characteristics of lines of latitude ?
Answer:

(a) The lines of latitude are parallel to the equator.
(b) The lines of latitude are drawn at an angular distance with respect to the equator.

Question 5.
Name the two hemispheres of the earth made by the Equator.
Answer:
Northern hemisphere and Southern hemisphere.

Question 6.
Express 1° angular distance in kilometres.
Answer:
As the circumference or the equator is nearly about 40,000 km.
So 1° angular distance in km. will be 40,000/360 =111 km. approximately.

Question 7.
Name the thermal zones of the earth.
Answer:
The thermal zones of the earth are Tropical, Temperate and Polar zones.

Question 8.
With the help of degrees, name the important lines of latitude.
Answer:

(a) Tropic of Cancer — 23 1/2°N
(b) Tropic of Capricorn — 23 1/2° S.
(c) Arctic Circle — 66 1/2° N.
(d) Antarctic Circle — 66 1/2° S
(e) North Pole — 90°N
(f) South Pole — 90°S

Question 9.
Which temperature zone receives almost vertical rays of the sun and which zones receive slanting rays ?
Answer:
The Tropical zone gets vertical rays of the sun, while temperate and polar zones receive slanting rays of the sun.

Question 10.
Which line is known as the Prime Meridian ? State its importance.
Answer:
Greenwich Meridian is called the ‘Prime Meridian’ or the 0° longitude. The time is calculated with respect to this Meridian. So it is the basic Meridian and time is written as G.M.T. (Greenwich Meridian Time) The earth takes 4 minutes for moving 1° distance.

Question 11.
How can the general climate of an area be described with the help of the lines of latitudes ?
Answer:
The temperature decreases northwards and southwards from the equator. The region within 23 1/2° N and 23 1/2° S will get tropical climate with ample temperature and rainfall. On the other hand the regions between
23 1/2° N – 66 1/2° N and 23 1/2° S – 66 1/2° S will get temperate climate, while the regions known as Arctic and Antarctic circles get very cold polar climate as Tundra region.

Question 12.
Which line of longitude is used to fix the World Standard Time ? State its value in degrees.
Answer:
Greenwich Meridian is used to fix the World Standard Time. Its value in degrees is 0°. This time is written as G.M.T.

Question 13.
State the longitudinal value in degrees of Indian Standard Meridian.
Answer:
Longitudinal value of Indian Standard Meridian is 82 1/2° E. It passes midway through India nearly along the city of Allahabad.

Question 14.
What is meant by IDL ? State its importance.
Answer:
IDL means the International Date Line, which is along 180° E & W. The date or day changes while crossing this line i.e. while there is Monday in the Eastern Hemisphere i.e.
0° – 180°E, there will be Sunday in the Western Hemisphere i. e. 0° – 180° W.

Question 15.
What are the Great Circle Routes ? State their importance.
Answer:
The Great Circle Routes follow the great circles i. e. the perimeters of the earth, which cover the shortest distances between any two places in spite of the zigzag routes along the surface of earth. These circles are beneficial for following the shortest distances between any two places and help in saving the time.
i. e. the shortest routes are covered in minimum time span.

Question 16.
What is a globe ? State the importance of a globe.
Answer:
A globe is a man-made spherical model of the earth. A globe is very useful model to display the actual shape of the earth with its tilted axis ; The rotation and revolution of the earth can be very clearly shown by it along with the continents and oceans.

II. Give reasons for each of the following

Question 1.
Lines of latitude carve out the heat zones of the earth.
Answer:
The Temperature goes on decreasing from the equator towards the poles. So the latitudinal zones are the actual heat zones of the earth, namely tropical, temperate and polar zones.

Question 2.
Lines of longitude are also called Meridians of longitude?
Answer:
The word ‘meridian’ means related to noon or 12 p.m. As every longitude receives the noon time or 12 p.m. at different intervals where the sun’s rays are exactly vertical over a particular longitude. On a particular longitude the noon-time is the same from north to south ; so a longitude is also called a Meridians of longitude.

Question 3.
Diametrically opposite lines of longitude and the Equator are called Great Circles.
Answer:
Every longitude along with its opposite longitude makes a complete circle around the earth and another complete big circle is the equator; while the latitudes make smaller circles along with the poles to be only points. So the equator and the longitudinal lines around the earth are called the Great Circles.

Question 4.
The Greenwich time is called Greenwich Mean Time.
Answer:
The time of any place or country is calculated according to the 0° longitude or Greenwich meridian, the time change is of 4 minutes for every 0° longitude. So it is called Greenwich Mean Time.

Question 5.
IDL deviates and goes zig-zag near some Islands in the Pacific ocean.
Answer:
IDL is not a straight line, but it deviates in order to classify some scattered Islands in a particular divisions of Hemispheres, so that the day and time can be calculated according to the line, as the natural position of the Islands is haphazard.

Question 6.
A globe is the most popular model of the earth.
Answer:
As our earth is spherical in shape, so it can be best represented by a spherical model like a globe. A globe illustrates the position of continents and oceans, the tilted axis of the earth, its rotation, the sea and air routes etc. So a globe is a perfect model of the earth.

III. Long Answer Questions 

Question 1.
Describe the lines of latitude, their importance and use.
Answer:
The face of the earth is divided into various parallel circles with respect to the equator on both sides at different angular distances. These lines are veiy important to decide the climate and temperature range of any place or region as the temperature goes on decreasing from the equator to polewards.

Question 2.
With reference to the International Date Line, state the following:

(a) It is meaning and application.
(b) The important deviations it makes and reasons for the same.
(c) Give an example of how time lost or gained is computed with reference to this line.

Answer:

(a) The time and date changes as we cross the International Date Line i.e. the navigators or pilots have to loose one day while crossing westwards and gain one day while crossing eastwards i.e. When one travels from Tokyo to San Francisco on Monday, he will reach San Francisco on Sunday.
(b) The International Date Line is not a straight line but have some deviations in order to adjust with the pattern of the landforms and some islands to decide for the time and date of these places and regions.
(c) If we are moving from Hawaii Islands towards Shanghai on Tuesday, we will reach there on Wednesday or Thursday probably, but if we are going eastwards from Shangai to Hawaii islands on Tuesday. We may reach there either on Tuesday or Monday.

Question 3.
Describe the lines of longitude and state their use in relation to distance and time.
Answer:
A longitude is the angular distance of a place east or we§t of the Prime Meridian or 0° longitude.
The lines of longitude are the great semi-circles joining North pole and South pole and are equal in length. These are 0° – 180°E and 0° – 180°W longitudes or total 360°. As the earth takes 24 hours to make a complete rotation along its axis crossing 360° lines of longitude, so earth takes nearly 4 minutes to move one degree (1 °) longitude or 111 km length or distance. There is difference of time of one hour between 15° interval of longitudes. According to the clock-time, EGA stands for East-Gain-Add and WLS means West Lose Subtract. In other words for each 10 longitude towards east 4 minutes are to be added and towards west for each 1° longitude 4 minutes are to be subtracted.

Question 4.
Make a detailed study of finding time with the help of longitudes. Give one practical example.
Answer:
Indian Standard Time is based on 82 1/2° E longitude. So if the time in India is 12 noon, so it will be 6.30 A.M. in England or GMT. The time difference between 0° and 82 1/2° E will be 82.5 × 4 – 330 minutes or 330 ÷ 60 = 5 1/2 hours. So there is difference of 5 1/2 hours between India and England, as England lies in the west, so the time will be 5 1/2 hours less than India.

IV. Problem Solving

An Example:
A cricket match was to be held at Birmingham at 9 a.m. local time. The position of Birmingham is 5° W. Calculate the time the viewers have to tune their television in Sydney 151°E.
Answer:
The local time at Birmingham is 9 am.
The location of Birmingham is 5° W of Prime Meridian.
The GMT would be 9:20 a.m.
[9.00hrs + (5° × 4min) = 9.00hrs + 20 min = 9.20 a.m. Sydney is located at 151 °E of Prime Meridian
At any point of time Sydney would be 151 × 4 = 604 min = 10 hrs 4 min ahead of GMT (Sydney is to the East of the Prime Meridian so local time would be ahead of GMT)
When it is 9:20 a.m. GMT the local time at Sydney would be (9:20 + 10:04) 19:24 hrs or 7:24 p.m.
in order to watch the Brimingham match at Sydney the viewers would have to tune their televisions at 7:24 p.m. local time.

Answer the following questions

Question 1.
An important programme was to be broadcast from Mumbai at 7.30 p.m. This was heard by some Indian sailors near Ivory Coast in West Africa at 20°W longitude. What was the local time there ?
Answer:
According to the Indian Standard Time 7.30 p.m. based on 82 1/2° E. Longitude was the time at Mumbai. The longitudinal difference between Mumbai and Ivory Coast at 20° W is 82.5 + 20 = 102.5. So 102.5 × 4 = 410.0 minutes = 6 hours 50 minutes, i.e. the time will be 6 hours 50 minutes less than 7.30 p.m. So the time will be 12.40 p.m

Question 2.
What is the longitude of a place where the local time 1:15 p.m. when it is 4 a.m. at Chicago (88°W) ?
Answer:
The time difference between the two places is 9 hours and 15 minutes or 540 + 15 = 555 minutes So the longitudinal difference will be 555/4 = 138.75° degrees. So the longitude of the required place will be 50° 45′ E i.e. it will cover 88° from west to 0° and 50° 45 east from 0° or Greenwich line.

Question 3.
Calculate the time at Durban (longitude 30°E) when the time is 7.00 a.m. at New York (75°W).
Answer:
The longitudinal difference between Durban and New York is 30° + 75°= 105°, so the time will be 105 x 4 = 420 minutes ahead from New York. There is the difference of 420 minutes or 7 hours, or 2 p.m.

Question 4.
Calculate the longitude of a place where the local time is 6.00 a.m., when the time is 9.00 p.m. at New Delhi on longitude 77° E.
Answer:
The time difference between the required place and New Delhi is 6 + 9 = 15 hours, so the time in minutes =15 × 60 = 900 minutes So the longitudinal difference = 900/4 = 225°. So the place will be in the west 225° – 77° = 148° W.

Question 5.
Calculate the local time at Singapore (104°E) when it is 6.00 p.m. at Greenwich.
Answer:
The longitudinal difference at Singapore and Greenwich is 104°, so the time difference is 104 × 4 = 416 minutes i.e. 6 hours 56 minutes. So the time at Singapore will be 12.56 a.m.

Question 6.
Calculate the location of a place where the local time is noon when it is 7.30 p.m. at Greenwich.
Answer:
Time difference is 12 – 7.30 = 4.30 or 4 hours 30 minutes = 240 + 30 = 270 minutes So the longitudinal difference is 270/4 = 67.5°. So the longitude is 67.5°W or 67 1/2° W.

Question 7.
What is the time and day at Mumbai (73°E) when it is Sunday 10.30 p.m. at Shillong (92°E) ?
Answer:
The longitudinal difference is 92° – 73° = 19°. So the time difference is 19 x 4 = 76 minutes or 1 hours 16 minutes or the time at Mumbai is 9.14 p.m.

Practice Questions (Solved)

Question 1.
How many lines of latitude are there ?
Answer:
180 + 1 = 181

Question 2.
How many lines of longitude are there ?
Answer:
360 – 1 = 359.

Question 3.
Which meridian is called Prime meridian ?
Answer:
0° meridian.

Question 4.
What is the latitude of equator ?
Answer:
0°

Question 5.
What is the latitude of Tropic of Cancer ?
Answer:
23 1/2° North.

Question 6.
What is the latitude of Tropic of Capricorn ?
Answer:
23 1/2° South.

Question 7.
Which is the longest line of latitude ?
Answer:
Equator.

Question 8.
Which star is located vertically above the North pole ?
Answer:
Pole-Star

Question 9.
Into how many time zones, has the world been divided?
Answer:
24

Question 10.
What do you mean by meridians ?
Answer:
Lines of longitude.

Question 11.
What is the relation between Temperature and Latitude of a place ?
Answer:
The temperature decreases with latitude.

Question 12.
What is latitude of North pole and South pole ?
Answer:
90° N and 90° S.

Question 13.
Why are there 180 parallels of latitude ?
Answer:
Because North pole to South pole (a hemisphere) has an angle of 180°.

Question 14.
Name the two hemispheres of the Earth made by the equator ?
Answer:
Northern Hemisphere and Southern Hemisphere.

Question 15.
Which temperature zone receives slanting rays ?
Answer:
Polar Zone.

Question 16.
Name the two reference lines with respect to which the distances of various places on the earth’s surface are measured ?
Answer:
Prime Meridian and Equator.

Question 17.
What is the rate of change of time per degree of longitude ?
Answer:
4 minutes per degree.

Question 18.
Why are the letters N or S added to latitude values ?
Answer:
The latitudes in Northern Hemisphere are marked N while the latitude in Southern Hemisphere marked S.

Question 19.
Why are letters E or W added to longitude values ?
Answer:
The longitudes in the Eastern Hemisphere are marked E while the longitudes in the Western Hemisphere are marked W.

Question 20.
What is the importance of Tropic of Capricorn ?
Answer:
It marks the Southern limit of tropical zone.

Question 21.
What is meant by “the Parallels of Latitude ?
Answer:
If you examine a globe or map, you will see two sets of lines drawn across it. One set of lines runs north and south of Equator and Parallel to it. These lines are called Parallels of a Latitude. The total number of such lines, if drawn at a distance of one degree, from one another is 180 : 90 North of the equator and 90 South of the equator.

Question 22.

(a) What do you mean by Longitude of a place ? How is longitude of a place determined ?
(b) What is the “Prime Meridian” ?
(c) What is the difference between Prime Meridian and other meridians of longitude ?
(d) Explain how latitudes and longitudes help to determine the position of a place on the globe ?
(e) Explain how the longitude of a place affects the time.

OR
State the rate of change of time with longitude.
Answer:

(a) Longitude is the distance of a place east and west of the Prime Meridian along a parallel of latitude. This distance is measured in degrees.
When we say that the Longitude of Delhi is 77° East, we mean that Delhi lies East of the Prime Meridian and its distance from the Prime Meridian is 77°
The Longitude of a place can be determined by comparing its Local Time with Greenwich Time. Greenwich Time can be known either by radio or by means of a watch which keeps Greenwich Time. Captains of ships generally use a Chronometer for this purpose. A Chronometer is a time piece which keeps accurate time and which is not affected by change in temperature. Now suppose that when it is 2 p.m. at Greenwich, another place shows 5 p.m. The difference between the times of two places is 3 hours, that is 180 minutes. Thus the place is =180 / 4 = 45° away from the Prime Meridian and since its time is ahead of Greenwich. Its longitude will be 45° East.
(b) The Prime (or First) Meridian is the meridian from which longitude is measured. It is numbered. 0° longitude. It is the meridian which passes through Greenwich (near London). Thus the Prime Meridian is also called Greenwich line.
(c) Other meridians of longitude are the lines which join all places having the same angular distance, east or west, of the Prime Meridian.
(d) The intersection of latitude and longitude points out the exact position of a place on the earth’s surface. For example London is situated at 51°30’N (latitude) and 0.5 W (longitude). With the help of these intersecting lines, it is convenient to locate the position of London on the map. Actually, latitude and longitude are both imaginary lines drawn on a map or a globe in order to locate the position of a place or a region on the earth’s surface.
(e) As the Earth rotates from west to east about its own axis, the zone of illumination moves slowly towards the west. This accounts for variation in the time of Sunrise and Sunset at different places on the Earth. The Earth takes 24 hours to complete one rotation. This means that 360 degrees of longitude are covered in a period of 24 hours. This gives rise to a time difference of [24 × 60/360] or 4 minutes for 1° of longitude. The time difference is to be added in case of places to the east of a point. In case of places to the west, the time difference is to be subtracted. It is possible to calculate the time at a given place A from the time recorded at B and the longitude difference between stations A and B.

Question 23.

(a) What is “Greenwich Mean Time” ?
(b) How far is it correct to say that local time is the Sun time ?
(c) How can you say that the use of ‘Local Time’ is very inconvenient nowadays in practical life ?
(d) Why do some countries have many time zones ?

OR
What are ‘Time Zones’ ?
Answer:

(a) Greenwich Mean Time (GMT):- It is based on 0° longitude of a place of this name near London. GMT is adopted uniformly by all countries to keep time. It forms the basis of fixing Time Zones.
(b) When the Sun reaches the highest point in the sky, while crossing the meridian of any place, it is mid-day or 12.00 noon at that place. If watches are adjusted according to this time, then it will be known as local time. But the highest position of the sun can be found only on a sunny day. Therefore it is correct to say that local time is the Sun-time.
(c) Use of Local time is very inconvenient now-a-days in practical life, because if we have to travel through many countries, it will be convenient to us to follow one particular standard time, according to which we can set our watches with respect to a particular country and its standard time with reference to Greenwich or Prime Meridian (0° Longitude) to bring about international uniformity. This is known as Greenwich Mean Time (GMT). The Indian Standard time is 5 hrs 30 minutes ahead of GMT.
(d) Large countries like Russia, Canada and the United States have vast longitudinal extent. They do not have a single Standard Time for the whole Country. They have many time zones, with each time zone covering about 15° of longitude. The erstwhile Soviet Union had 11 times zones to cover 165° of longitudinal extent. Canada and the United States have five time zones extending from the Atlantic coast of the Pacific coast. There is time difference of five hours between the two coasts.

Question 24.
Give reasons for the following :

(a) There are no latitudes higher than 90°N and 90°S.
(b) The opposite meridians of longitude form a Great Circle.
(c) Local time is a theoretical reality, while Standard Time is a practical necessity.
(d) “The International Date Line is not a straight line coinciding with longitude 180 degrees.” Why ?
(e) The distance between two consecutive meridian, is equal to about 111 kilometres only at the equator.
(f) When it is noon at Cairo (30°E), the local time in New York (75°W) is 5.00 a.m.
(g) All parallel other than equator are not Great Circles.
(h) A person, travelling from Mumbai to London, alters the time on his watch at several places.

Answer:

(a) The total circumference of a circle is 360° and the distance between the Equator and the North Pole is one-fourth of the circumference i.e. 90°. So we have 90 latitudes towards north and 90 towards south, which are denoted as 90° N and 90° S respectively.
(b) The opposite meridians of longitude form a Great circle because by each of them the world is divided into two equal parts
(c) Local time may differ from place to place. Therefore, it is only a theoretic reality. On the other hand, standard time is the same for a particular country. It is a practical necessity for the sake of uniformity of time.
(d) The International Date Line passes through the Pacific ocean where there are no land masses. It follows 180° meridian for most of its distance. The date line is zig-zag in some places to avoid the confusion of time on the same island. It avoids some islands and deviates from 180°. In Northern Hemisphere, it bends to the West of 180° while in the Southern Hemisphere it bends Eastwards.
(e) The circumference of the Earth is approximately 40,000 km. It covers ah angle of 360 degrees. The distance between two consecutive parallels of latitude is everywhere the same. This is because lines of latitude are parallel lines. Therefore one degree of latitude. = 40,000/360 = 111km (approximately.)
On the other hand, the distance between two consecutive meridians of longitude is 111 km only at the equator and gradually decreases with distance from the equator. This is because the meridians of longitude converge at the two poles.
(f)

Longitude of Cairo = 30° E
Longitude of New York = 75° W
Difference in Longitude = 30° + 75° = 105°
(Add because Cairo is in the East of Greenwich and New York is in the West of Greenwich).
∴ Difference in time = 105 × 4 = 420 minutes = 7 hours
As New York is situated in the West of Greenwich, its local time will be behind that of Cairo. So we subtract.

(h) it is because of change in longitude at several places

Question 25.
What do you mean by the Latitude of place ?
Answer:
Latitude is the distance of a place north or south of the equator along a meridian. This distance is measured in degree. When we say that the Latitude of Delhi is 28-j North, we mean that Delhi lies North of the equator and its distance from the equator is 28 1/2.

Question 26.
How are Latitudes measured ?
Answer:
The latitude of a place is the angular distance of the point north or south of the equator measured in degrees. The equator is taken as 0° latitude. Latitudes are measured from 0 ° to 90° N and 0° to 90° S. The distance from the equator to 90° N covers a distance of 1/4 of the circumference of the Earth or 140,000 km. One degree of latitude is equivalent to the length of about 111 km or 69 miles.

Question 27.
Explain why the lines of longitude are called meridians of longitude ?
Answer:
Lines of longitude are lines which join all places having the same angular distance east or west of the Prime Meridian. All lines of longitude are semicircles of equal length. Lines of longitude are also called Meridians because all places along a lines of longitude experience mid-day at the same time.

Question 28.
State two properties of lines of latitude.
Answer:

1. The length of the lines of latitudes decrease with distance from the equator.
2. All lines of latitude are circles parallel to the equator.

Question 29.
State two properties of lines of longitude.
Answer:

1. The distance between two consecutive longitude decreases gradually with distance from the equator.
2. All lines of longitude are semicircles of equal length.

Question 30.
Clearly distinguish Longitude from Lines of Longitude.
Answer:
Longitude is the distance of a place from the Prime Meridian while lines of longitude are lines drawn on a map or globe showing the longitude of all the places at the distance from the Prime Meridian. These lines join the north and south poles and cut the Equator at right angles.

Question 31.
What do you mean by “Meridians or Lines of Longitude” ?
Answer:
The other set of lines join the north and south poles and cuts the equator at right angles. These lines are called Lines of Longitude or Meridians. The total number of such lines, if drawn 1° apart, is 360° – 180° East and 180° West of the Prime Meridian. It should be noted that 180° East and 180° West in the same lines.

Question 32.
What is the latitude of :

1. Equator
2. North Pole
3. South Pole
4. Tropic of Cancer
5. Tropic of Capricorn
6. Arctic Circle
7. Antarctic circle ? Also give their characteristics.

Answer:

1. Latitude of Equator The latitude of the equator is 0°. Here the days and nights are equal throughout the year and the rays of the sun fall exactly vertically at noon on March 21 and September 23.
2. Latitude of North Pole The latitude of the North pole is 90° North because it is situated north of the Equator at a distance of a quarter of the circumference of the earth. Here days and nights are of six-months duration.
3. Latitude of South Pole Latitude of the south pole is 90° south, because it is situated South of Equator at a distance of a quarter of the circumference of the earth. Here the days and night are of six months duration.
4. The Latitude of the Tropic of Cancer is 23 1°/2 North. Here the rays of the sun fall vertically at noon on June 21.
5. The Latitude of the Tropic of Capricorn is 23 1°/2 South.
   Here the rays of the sun fall vertically at noon on December 22.
6. The Latitude of the Arctic Circle is 66 1°/2 North. Here once the year (June 21) the day is of 24 hours duration and once in the year (December 22) the night is of 24 hours duration.
7. The Latitude of the Antarctic Circle is 66 1°/2 South. Here once in the year (December 22nd) the day is of 24 hours duration and once in year (June 21) the night is of 24 hours duration.

Question 33.
What adjustment has to be made when ships cross the International Date Line ?
OR
Explain why a day appears to be lost in sailing round the world from east to west and gained when travelling from west to east.
Answer:
The earth rotates on its axis from west to east, hence places in the east have their sun rise earlier than places in the west. Now if a man travels round the world from east to west, for every degree of longitude covered; he will have to set back his watch by four minutes. Thus after covering 360°when he returns to the place from where he started he will have to set back his watch 360 x 4 / 60 = 24 hrs. Thus he will appear to have lost a day. When Francis Drake returned to England after circumnavigating the globe, he thought it was Saturday, where as actually it was Sunday. The reason was that he had traveled from east to west, and had under calculated a day. On the other hand if a man travels from west to east, for every degree of longitude covered he will put forward his watch by four minutes and for 360° he will forward it 24 hrs. When he returns to the place from where he started he will appear to have gained a day. When Cap. Basil Hailed reached Manila after circumnavigating the globe, he thought it was Monday; where as actually it was Sunday. The reason was that he had traveled from west to east and had over calculated a day.

Question 34.
Define Equator. What is its main function ?
Answer:
Equator is the parallel of zero degree latitude. It is an imaginary circle round the Earth bisecting it into halves i.e. Northern * Hemisphere and Southern Hemisphere. It serves as reference line for the location of different places on the earth.

Question 35.
What will be local time at Delhi 77° E longitude when is 3 p.m. at Tokyo 139°E longitude ?
Answer:
Longitude of Delhi = 77°E
Longitude of Tokyo = 139°E
Difference per degree – 139°- 77° = 62°
Difference of time per degree = 4 minutes , Difference between the time of Delhi and Tokyo = 4 × 62 = 248 minutes = 4 hours 8 minutes
Since Delhi lies west of Tokyo we shall subtract 4 hours 8 minutes from Tokyo time. Hence local time at Delhi is 10.52 a.m.

Question 36.
What will be the local time at Madras 80°E ? When it is 9 P.M. at New York 74° W ?
Answer:
Longitude of Madras = 80° E
Longitude of New York = 74° W
Difference in Degrees = 80° + 74° = 154°
Difference in time per degree = 4 minutes
Difference between the times of two places = 40 x 154 = 616 = 10 hour 16 minutes
Since Madras lies East of New York, we shall add 10 hours 16 minutes to the local time of New York. The local time at Madras will therefore, be 7.16 A.M. next morning.

Question 37.
“The degree of longitude decreases in length poleward”. Why?
Answer:
Equator is the longest parallel on the Earth. All other parallels become shorter polewards due to spherical shape of the Earth. So the meridians near the poles have a narrow space. One degree of longitude is the longest at the equator (111 km) at 45° latitude it is 79 km, at 60° latitude it is 55 km and at poles, it is zero km.

Question 38.
What is the relation between longitude and time ?
Or
“There is a difference of 4 minutes of time for one degree of longitude”. Why ?
Answer:
There is a close relation between longitude and time. The Earth makes one complete rotation of 360 degrees in 24 hours. It passes through 15 degrees is one hour or one degree in four minutes. Thus, there is a difference of 4 minutes of time for one degree of longitude. As the Earth moves from West to East, the places East of Greenwich gain time whereas the places West of Greenwich loose time.

Question 39.
“Lines of latitude are called parallels of latitude” Why?
Answer:
Lines of latitudes join the places of same latitude. These are circles drawn round the earth, parallel to the equator. Therefore, these are called parallels of latitude.

Question 40.
A ship crossing international date line at mid-night on Wednesday Eastwards, find that it is mid-night Tuesday on American side. Why ?
Answer:
A ship crossing international date line from West to East gains a day. It repeats a day. A day is subtracted from the calendar. So when it is Wednesday mid-night on Asiatic side, it is Tuesday midnight on the American side.

Question 41.
Mid-days Sun can be seen overhead in Chennai twice a year, but not even once in Delhi. Why ?
Answer:
Tropic of Cancer is the Northernmost limit of overhead Sun. Sun’s rays do not fall vertical beyond 23 1/2° N latitude. Delhi is located North of Tropic of Cancer, so the Sun is never overhead at Delhi. But Chennai has overhead Sun twice a year.

1. When the Sun moves northward, from equator to Tropic of Cancer, the Sun is overhead at Chennai.
2. When the Sun shifts from Tropic of Cancer to equator, then again Chennai has overhead Sun.

Question 42.
Explain why there is no higher latitude other than 90° N and 90° S.
Answer:
Latitude is the angular distance from the plane of the equator. All of surfaces (planes) or circles make a maximum angle of 90° from the plane of the equator. Therefore, maximum latitude is 90° N in the Northern Hemisphere and 98° Southern Hemisphere.

Question 43.
Name the five important parallels of latitude.
Answer:

(a) Equator is the starting line for all the parallels. It is zero degree parallel.
(b) Tropic of Cancer – 23 1/2° North parallel.
(c) Tropic of Capricorn – 23 1/2° South parallel.
(d) Arctic circle – 66 1/2° North parallel.
(e) Antarctic circle – 66 1/2° South parallel.

Question 44.

(a) What do you mean by local time ?
(b) What is the local time when it is noon at a place ?
(c) What are the main characteristics of local time ?

Answer:
(a) Local time : The local time of a place is the time of its own meridian. The local time is calculated by the position of the Sun at noon at a given place. When the Sun at any place is highest in the sky. It is noon.
(b) It is 12 o’clock. All the watches of that place should be set according to that time.
(c) Characteristics :

1. Every meridian has a different local time.
2. The places on the same meridian have the same local time.
3. The Eastern places will be ahead of Western places for local time.
4. Sundial was a simple and old method to determine local time.

Question 45.

(a) What is the rule of changing the date while crossing the international date line ?
(b) What is meant by ‘six-day week’ and ‘eight-day week’?
(c) Explain the above with the help of a map.

Answer:
Rule : On crossing the date line, the ships adjust the dates according to the following rules :

(a) When crossing westward, towards Asia (from U.S.A. to Japan), a day must be added.
When crossing the date line, ship misses a day from the calendar and have ‘six day week’. If a ship crosses the date line on Monday, the next day will be Wednesday and not Tuesday.
(b) When crossing eastward towards America (from Japan to U.S.A.) a day must be subtracted. When crossing the date line ships gain a day from the calendar and have an ‘eight- day week’. It repeats a day. If ship crosses the date line on Monday, the next day will be again Monday and not Tuesday.