Samacheer Kalvi 7th Social Science Term 1 Geography Solutions Chapter 1 Pdf
Tamilnadu Board Samacheer Kalvi 7th Social Science Term 1 Geography Solutions Chapter 1: Tamilnadu State Board Solution Class 7 Social Science Term 1 Geography Chapter 1 – Interior of the Earth.
Samacheer Kalvi 7th Social Science Geography Solutions Chapter 1: Overview
Board |
Samacheer Kalvi |
Class |
7 |
Subject |
Social Science Geography |
Term |
1 |
Chapter Name |
Interior of the Earth |
Unit 1: interior of the Earth
Multiple choice questions:(marks:1)
1.) The Earth have how many concentric layer:
A.) 2
B.) 3
C.) 4
Ans: 3
2.) The outermost layer of the Earth is:
A.) The crust
B.) The mantle
C.) The core
Ans: The crust.
3.) The middle layer of the Earth is:
A.) The core
B.) The crust
C.) The mantle
Ans: The mantle.
4.) The innermost layer of the Earth is:
A.) The crust
B.) The mantle
C.) The core
Ans: The core.
5.) The radius of the Earth is:
A.) 6371 km
B.) 2900 km
C.) 5150 km
Ans: 6371 km.
6.) Assertion(A): The inner core of the Earth is also known as Nife.
Reason(R): Nife is composed of nickel and ferrous.
a.) Both A and R are true and R is the correct explanation of A.
b.) Both A and R are true but R is not the correct explanation of A.
c.) A is true and R is false.
d.) A is false but R is true.
Ans: Both A and R are true and R is the correct explanation of A.
7.) Assertion (A): Earth is called a blue Planet.
Reason(R): 71% of the earth is covered by water.
A.) Both A and R are true and R is the correct explanation of A.
B.) Both A and R are true but R is not the correct explanation of A.
C.) A is true but R is false.
D.) R is true but A is false.
Ans: Both A and R are true and R is the correct explanation of A.
Answer the following questions: (marks:1)
1.) What are the concentric layers of the Earth?
Ans: There are three concentric layers of the Earth. They are:
A.) The crust
B.) The mantle
C.) The core
2.) What are the two main types of crust?
Ans: Two main types of crust are:
A.) The continental crust and
B.) The oceanic crust.
3.) What is called mohorovicic discontinuity?
Ans: The crust (the outer layer of the Earth) is separated from the mantle (the middle layer of the Earth) by a boundary called mohorovicic discontinuity.
4.) What is barysphere?
Ans: The innermost layer of the Earth is also known as the barysphere.
5.) What is known as Weichert Gutenberg discontinuity?
Ans: The core ( the innermost layer of the Earth ) is separated from the mantle (the middle layer of the Earth ) by a boundary called Weichert Gutenberg discontinuity.
6.) The lithosphere is broken into a number of plates known as ……………
Ans: lithospheric plates.
7.) What is termed as tectonic movement?
Ans: The movement of the Earth’s lithospheric plates is known as tectonic movement.
8.) What is known as an earthquake?
Ans: A sudden movement of a portion of the Earth’s crust which produces a shaking or trembling is known as an earthquake.
9.) What is the Richter scale?
Ans: The magnitude of an earthquake is measured by the Richter scale. The numbers on this scale range from 0 to 9.
10.) What is known as the epicentre of the earthquake?
Ans: The point of the Earth’s surface directly above the focus is called the epicentre of the Earthquake.
11.) What is known as the focus of the earthquake?
Ans: The point where the vibration of the earthquake originates is known as the focus of the Earthquake.
12.) The waves of the earthquake are recorded by an instrument named…………
Ans: seismograph.
13.) What is known as volcano?
Ans: A volcano is a vent or an opening in the earth’s crust through which hot magma erupts from deep below the surface. Volcanic eruptions may also take place through a long crack or fissure through which steam and other materials flow out.
14.) What is volcanology?
Ans: The scientifi c study of volcanoes are called volcanology.People who study volcanoes are called volcanologists.
15.) Which is the world’s biggest active volcano?
Ans: Mauna Loa in Hawaii is the world’s biggest active volcano.
Answer the following questions: (marks:2/3)
1.) What is Sial and Sima?
Ans: The crust or the outermost layer of the Earth comprises two distinct parts. The upper part consists of granite rocks and forms the continents. It has the main mineral constituents of silica and alumina. So it is referred to as Sial. It has an average density of 2.7g/cm3.
The lower part is a continuous zone of denser basaltic rocks forming the ocean floors, composed mainly of silica and magnesium. It is therefore called Sima. It has an average density of 3.0g/cm3.
2.) What are endogenic and exogenic forces?
Ans: The forces which act in the interior of the earth are called Endogenic forces and the forces that work on the surface of the earth are called Exogenic forces.
3.) What are the causes of earthquakes?
Ans: A sudden movement of a portion of the earth’s crust which produces a shaking or trembling is known as an earthquake.The main cause of earthquakes are:
- sudden slipping of the portion of the earth’s crust along fractures or faults.
- The movement of the molten rocks underneath the surface produce strains which break the rocks apart.
- The sudden shifting of landmass causes effusion in the crust of the earth sending vibrations or waves into the surrounding portions of the earth. Sometimes the surface of the earth itself cracks.
4.) What are the effects of earthquakes?
Ans:A sudden movement of a portion of the earth’s crust which produces a shaking or trembling is known as an earthquake. The effects of earthquake are: Earthquakes may cause changes in the earth’s surface. Vibrations often set landslides in mountainous regions.
- A greater danger in an earthquake is the falling of buildings. Most of the houses which collapsed were made of mud and bricks and proved to be death traps.
- Underground water system is naturally disturbed by such movements.
- Fire is another great danger
- An earthquake which originates below or near the sea causes great disturbance in the water. The floods and waves cause great loss of life, sometimes more than the earthquake itself. Tsunami, a Japanese term, is the name given to the huge waves caused in the sea by an earthquake. Tsunamis are quite common along the coasts of Japan and other regions in the Pacific Ocean.
- Loss of lifes and materials.
These are the main effects of earthquakes.
5.) What are the types of earthquake waves?
Ans: There are three types of earthquake waves:
- P waves or longitudinal waves
- S waves or transverse waves
- L waves or surface waves.
6.) What is known as tsunami?
Ans: Tsunami, a Japanese term, is the name given to the huge waves caused in the sea by an earthquake. Tsunamis are quite common along the coasts of Japan and other regions in the Pacific Ocean.On 26th December 2004, Tsunami in the Indian Ocean swept coastal area of Indonesia, India, Sri Lanka, Thailand etc. They caused immense damage to life and property in the coastal area.
7.) In India, what are the earthquake prone regions?
Ans: In India, the Himalayan region and the Ganga-Brahmaputra valley are prone to earthquakes. A number of earthquakes have been experienced in this region. Some of them were very severe and caused extensive damage, e.g., the earthquake of UttarKashi in 1991 and Chamoli in 1999.
8.) What is magma and lava?
Ans: The molten rock material within the earth, together with gases, it is called magma. After
it rises to the surface, it is called lava.
9.) What are the differences between crater and caldera?
Answer-
10.) What are the causes of volcanic eruptions ?
Ans: The main causes of volcanic eruption are:
- The temperature increases as the depth increases at the rate of 1ºc for every 32 metres.
- There is also great pressure. At a depth of about 15 km the pressure is about 5 tonnes per cm 2 of rock. Under these circumstances, the interior of the earth is in a semi-molten state called magma.The magma, under great pressure has the capacity to dissolve great volume of gas; some gases are also combustible. This makes volcanic material burst forth through the weak spots in the earth’s crust.
Answer the following questions: (marks: 5)
1.) What are the major zones of volcanic activities in the world? (5)
Ans: Volcanoes are located in a clearly defined pattern around the world. They are closely related to regions that have been intensely folded or faulted. There are about 600 active volcanoes and thousands of dormant and extinct ones. They occur along the coastal mountain ranges, as off -shore islands and in the midst of oceans, but there are a few in the interior of continents. The volcanic belts are also the principal earthquake belts of the world. There are three major zones of volcanic activities in the world. They are:
A.) The Circum Pacific belt
B.) The Mid continental belt
C.) The Mid Atlantic belt
A.) Circum Pacific Belt: This is the volcanic zone of the convergent oceanic plate boundary. It includes the volcanoes of the eastern and western coastal areas of the Pacific Ocean. This zone is popularly termed as the Pacific Ring of Fire which has been estimated to include two-thirds of the world’s volcanoes.
B.) Mid continental belt: This is the volcanic zone of convergent continental plate boundaries that includes the volcanoes of Alpine mountain chains, the Mediterranean Sea and the fault zone of eastern Africa. The important volcanoes are Vesuvius, Stromboli, Etna, Kilimanjaro and Kenya. Surprisingly, the Himalayas have no active volcanoes at all.
C.) Mid Atlantic Belt: This belt represents the divergent boundary of plates located along the midAtlantic ridges. Volcanoes of this area are mainly of fissure eruption type. Iceland is the most active volcanic area and is located on the mid-Atlantic ridge. St. Helena and Azores Island are other examples.
2.) What is a volcano? What are the types of the volcano? (2+3)
Ans: A volcano is a vent or an opening in the earth’s crust through which hot magma erupts from deep below the surface. The opening is usually circular in form. Volcanic eruptions may also take place through a long crack or fissure through which steam and other materials flow out.
Types: Volcanoes are classified according to their periodicity of eruptions and the state of activity such as
- Active Volcano
- Dormant Volcano
- Extinct Volcano
A.) Active Volcano: Volcanoes that erupt frequently are called active volcanoes. Most of the active volcanoes lie in the Pacific Ring of Fire belt which lies along the Pacific coast. There are about 600 active volcanoes in the world, such as Mt. Stromboli in Mediterranean Sea, St.Helens in USA, Pinatubo in Philippines. Mauna Loa in Hawaii is the world’s biggest active volcano.
B.) Dormant Volcano:These volcanoes have shown no sign of activity for many years but they may become active at any time. These are called Sleeping Volcanoes. Vesuvius mountain of Italy, Mt Fujiyama of Japan, Mt. Krakatoa of Indonesia are famous examples of this type.
C.) Extinct volcano: A Volcano has not erupted in past 1000 years are often listed as Extinct volcanoes. The top of extinct volcanic mountains have been eroded. Mt Popa of Myanmar and Mt. Kilimanjaro and Mt. Kenya of Africa are examples of extinct volcanoes.
3.) What is an earthquake? What are the causes of earthquakes? Write down the effects of the earthquake? (1+2+2)
Ans: A sudden movement of a portion of the earth’s crust which produces a shaking or trembling is known as an earthquake.
Causes:
- sudden slipping of the portion of the earth’s crust along fractures or faults.
- The movement of the molten rocks underneath the surface produce strains which break the rocks apart.
- The sudden shifting of landmass causes effusion in the crust of the earth sending vibrations or waves into the surrounding portions of the earth. Sometimes the surface of the earth itself cracks.
Effects:
- Earthquakes may cause changes in the earth’s surface. Vibrations often set landslides in mountainous regions.
- earthquakes cause buildings falling. Most of the houses which collapsed were made of mud and bricks and proved to be death traps.
- Underground water system is naturally disturbed by such movements.
- Fire is another great danger
- An earthquake which originates below or near the sea causes great disturbance in the water. The floods and waves cause great loss of life, sometimes more than the earthquake itself. Tsunami, a Japanese term, is the name given to the huge waves caused in the sea by an earthquake. Tsunamis are quite common along the coasts of Japan and other regions in the Pacific Ocean.
- Loss of lifes and materials.
4.) Write a short note about the interior of the Earth?
Ans: The structure of the earth may be compared to that of an apple.On the basis of the study of earthquake waves the spherical earth is found to be three concentric layers.
They are:
A.) The crust,
B.) The mantle and
C.) The core.
A.) The Crust: The crust is the outermost layer of the earth. Its thickness varies from 5to 30 km.The crust comprises two distinct parts. The upper part consists of granite rocks and forms the continents. It has the main mineral constituents of silica and alumina. So it is referred to as Sial. It has an average density of 2.7g/cm3. The lower part is a continuous zone of denser basaltic rocks forming the ocean floors, consisting mainly of silica and magnesium. It is therefore called Sima. It has an average density of 3.0g/cm3.
B.) The Mantle: The next layer beneath the crust is called the mantle. It is separated from the crust by a boundary called Mohorovicic discontinuity. The mantle is about 2,900 km thick. It is divided into two parts. (i) The upper mantle with a density of 3.4 – 4.4g/cm3. extends down to 700 km. (ii) The lower mantle having a density of 4.4 – 5.5g/cm3 extends from 700 to 2,900 km.
C.) The Core: The innermost layer of the earth is called the core. It is also known as bar sphere. It is separated from the mantle by a boundary called Weichart Gutenberg discontinuity. The core is also divided into two parts. (i) The outer core, which is rich in iron, is in liquid state. It extends between 2,900 – 5,150 km. (ii) The inner core, composed of Nickel and Ferrous, also known as nife, is solid in state. The central core has very high temperature and pressure. It extends from 5,150 km to 6,370 km. The average density of the core is 13.0 g/cm3.
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