NCERT Solutions for Class 7 Social Science Our Environment Chapter 3

Our Changing Earth Class 7

Chapter 3 Our Changing Earth Exercise Solutions

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Exercise : Solutions of Questions on Page Number : 17

Q1 :  

Answer the following questions.

(i) Why do the plates move?

(ii) What are exogenic and endogenic forces?

(iii) What is erosion?

(iv) How are flood plains formed?

(v) What are sand dunes?

(vi) How are beaches formed?

(vii) What are ox-bow lakes?


Answer :

(i)The Lithospheric plates move around because of the movement of the molten magma inside the Earth.

(ii)Earth's movements are divided on the basis of the forces which cause them. The ones that work on the Earth's surface are called exogenic forces while the ones that work in the Earth's interior are called endogenic forces. The erosional and depositional activities of wind and water are examples of exogenic forces. Earthquakes and volcanoes are examples of endogenic forces.

(iii)Erosion is the weathering or wearing away of the landscape by different agents like wind, water and ice.

(iv)During its course through a plain, a river sometimes overflows its banks. This leads to the flooding of the neighbouring areas. As it floods, the river water deposits layers of fine soil and sediments on its banks. This leads to the formation of a flat, fertile flood plain.

(v)In deserts, when wind blows, it lifts and transports sand from one place to another. When it stops blowing, the sand particles fall and get deposited in low hill-like structures called sand dunes.

(vi)The erosional and depositional activities of the sea waves give rise to different coastal landforms. A beach is one such coastal landform. It is formed when the sea waves deposit sediments along the sea shore.

(vii)An ox-bow lake is a crescent-shaped lake formed by a meandering river. During its journey through a plain, a river twists and turns to form meanders. Erosion and deposition occur constantly along the sides of a meander, thereby causing the ends of its loop to come closer and closer. In due course of time, the meander loop cuts off from the river and forms a cut-off, crescent-shaped ox-bow lake.

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Q2 :  

Tick the correct answer.

(i) Which is not an erosional feature of sea waves?

(a) Cliff

(b) Beach

(c) Sea cave

(ii) The depositional feature of a glacier is

(a) Flood plain

(b) Beach

(c) Moraine

(iii) Which is caused by the sudden movements of the Earth?

(a) Volcano

(b) Folding

(c) Flood plain

(iv) Mushroom rocks are found in

(a) Deserts

(b) River valleys

(c) Glaciers

(v) Ox-bow lakes are found in

(a) Glaciers

(b) River valleys

(c) Deserts


Answer :

(i) Which is not an erosional feature of sea waves?

(a) Cliff

(b) Beach

(c) Sea cave

(ii) The depositional feature of a glacier is

(a) Flood plain

(b) Beach

(c) Moraine

(iii) Which is caused by the sudden movements of the Earth?

(a) Volcano

(b) Folding

(c) Flood plain

(iv) Mushroom rocks are found in

(a) Deserts

(b) River valleys

(c) Glaciers

(v) Ox-bow lakes are found in

(a) Glaciers

(b) River valleys

(c) Deserts

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Q3 :  

Match the following.

(i) Glacier

(a) Sea shore

(ii) Meanders

(b) Mushroom rock

(iii) Beach

(c) River of ice

(iv) Sand dunes

(d) Rivers

(v) Waterfall

(e) Vibrations of Earth

(vi) Earthquake

(f) Sea cliff

-

(g) Hard bed rock

-

(h) Deserts


Answer :

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Q4 :  

Give reasons.

(i) Some rocks have a shape of a mushroom.

(ii) Flood plains are very fertile.

(iii) Sea caves are turned into stacks.

(iv) Buildings collapse due to earthquakes.


Answer :

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Q5 :  

Activity.

Observe the photographs given below. These are various features made by a river. Identify them and also tell whether they are erosional or depositional or landforms formed by both.

Photograph

Name of the Feature

Type

[Erosional or Depositional or Both]

-

-

-

-

-

-


Answer :

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Q6 :  

For fun.

Solve the crossword puzzle with the help of given clues.

Across

Down

2. Loop like the bend of a river

1. Rise and fall of water caused by friction

of wind on water surface

4. Solid form of water

3. Flow of water in a channel

7. Moving mass of ice

5. Steep perpendicular face of a rock along

sea coast

9. Sudden descent of water in the bed of a river

6. Debris of boulder and coarse material

carried by glacier

11. Natural cavity on weak rocks formed by action of waves

8. Crescent-shaped lake formed by a meandering river

12. Embankment on a river that keeps it

in its channel

10. Fine sand deposited by the action of the wind

13. Large body of sea water

13. Isolated mass of rising steep rock near a

coastline

14. Dry area where sand dunes are found

14. Alluvial tracts of land formed by river deposits at mouth of the river

15. Small hill of sand caused by the action of the wind

-

16. Flat plain formed by river deposits during time of flood

-


Answer :

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