NCERT Solutions Class 7 Social Science (Geography)
The NCERT Solutions in English Language for Class 7 Social Science (Geography – Our Environment) Chapter – 3 (Our Changing Earth) has been provided here to help the students in solving the questions from this exercise.
Chapter – 3 (Our Changing Earth)
Exercises
1. Answer the following questions.
(i) Why do the plates move?
Answer – The plates move due to endogenic forces acting in the interior of the earth.
(ii) What are exogenic and endogenic forces?
Answer – The forces that act in the interior of the earth are called endogenic forces. The forces that act on the earth’s surface are called exogenic forces.
(iii) What is erosion?
Answer – Erosion is the wearing away of the landscape by different agents like water, wind, and ice.
(iv) How are flood plains formed?
Answer – 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) What are sand dunes?
Answer – 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) How are beaches formed?
Answer – The sea waves deposit sediments along the seashores. This results in the formation of beaches.
(vii) What are the ox-bow lakes?
Answer – When the river enters the plains, it twists and turns forming large bends known as meanders. In due course of time, the meander loops start to cut off the river and form cut off lakes, known as the ox-bow lakes.
2. Tick the correct answer.
(i) Which is not an erosional feature of sea waves?
(a) Cliff
(b) Beach
(c) Sea cave
Answer – (b) Beach
(ii) The depositional feature of a glacier is:
(a) Flood plain
(b) Beach
(c) Moraine
Answer – (c) Moraine
(iii) Which is caused by the sudden movements of the earth?
(a) Volcano
(b) Folding
(c) Flood plain
Answer – (a) Volcano
(iv) Mushroom rocks are found in:
(a) Deserts
(b) River valleys
(c) Glaciers
Answer – (a) Deserts
(v) Ox bow lakes are found in:
(a) Glaciers
(b) River valleys
(c) Deserts
Answer – (b) River valleys
3. 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 bedrock | |
| (h) Deserts |
Answer –
| (i) Glacier | (c) River of ice |
| (ii) Meanders | (d) Rivers |
| (iii) Beach | (a) Sea shore |
| (iv) Sand dunes | (h) Deserts |
| (v) Waterfall | (g) Hard bedrock |
| (vi) Earthquake | (e) Vibrations of earth |
4. Give reasons.
(i) Some rocks have the shape of a mushroom.
Answer – Some rocks have a shape of a mushroom because winds erode the lower section of the rock more than the upper part. Therefore, such rocks have a narrower base and wider top.
(ii) Flood plains are very fertile.
Answer – Flood plains are formed by the deposition of fine soil and other material called sediments on the river banks. As the soil and sediments are brought by floodwater, they are very fertile.
(iii) Sea caves are turned into stacks.
Answer – When the cavities in the sea caves become bigger and bigger, only the roof of the caves are leftover, which forms sea arches. Further, due to erosion, the roof vanishes and only the walls stay intact, turning the sea caves into stacks.
(iv) Buildings collapse due to earthquakes.
Answer – When the lithospheric plates move, the surface of the earth vibrates and then these vibrations travel outwards from the epicentre in the form of waves, which leads to sudden movement and results in the collapse of buildings.
