Class 11 | Geography | Questions and Answers | NCERT | AHSEC
1. What are body waves?
The waves that originated at the epicenter are called body or primary waves. Such waves move in all directions from the focus and travel throughout the body of the earth. Body waves are of two types – S and P waves. P waves are too fast and they reach the earth’s surface first. They can pass through any material. S waves take some time to reach.
2. Name the direct sources of information about the interior of the earth.
To gather information about the interior of the earth, it is necessary to dive deep into it. surface rock and mining. Among the direct sources, mining and volcanic eruptions can be taken into account. Scientists on the other hand, have undertook various projects like “Deep Ocean Drilling Projects” and “Integrated Ocean Drilling Project”. The collection of various materials through such activities has revealed the nature of the interior of the earth.
3. What is a “shadow zone”?
Earthquakes waves get recorded in seismographs at distant locations. These devices are positioned in various places. But it is seen that in certain locations, the seismograph cannot detect the waves. Such a place is called a “shadow zone”.
4. Briefly explain the indirect sources of information of the interior of the earth other than those of seismic activity.
Except seismic activity, the other indirect sources of information of the interior of the earth are –
- Mining activities – By analyzing the various properties of matter like density, structure etc., we can indirectly get information about the interior of the earth.
- Meteors – The structure of the substances in meteors and the structures of the substances of the interior of the earth have been found to be similar. So, we can get good information from the meteors.
- From other indirect sources like gravitation and magnetic field, we can understand the distribution of matter.
5. What are the effects of propagation of earthquake waves on the rock mass through which they travel?
The earthquake waves are mainly of two types – Body waves and Surface waves. Due the propagation of such waves through the rock mass, vibration occurs and as a result, extreme pressure is generated. As a consequence, it causes density differences in the material leading to stretching and squeezing of the material. Earthquake waves shake the rocks creating fault, fold, etc.
6. What do you understand by intrusive forms? Briefly describe various intrusive forms.
The lava from the volcanoes turns into volcanic stones after cooling. Sometimes, the lava cools inside the earth’s core and take various shapes or forms which are called as intrusive forms.
The various intrusive forms are –
- Batholiths – Sometimes the magma materials do not come out of the crust and take the form of a large dome after cooling. These magma chambers are called batholiths.
- Dykes – When the lava makes its way through cracks and fissures in the land, it solidifies almost perpendicular to the ground. It starts to cool in the same position forming wall-like structures. Such structures are called dykes.
- Lacoliths – They are large dome-shaped intrusive bodies with a level base that remain connected by a pipe like conduit from below. Their shape resemble that of volcanic domes.
Apart from these, various others intrusive forms like Lapolith, Phaeolith, Sills, etc. can be found.
7. Explain the interior structure of the earth?
We can divide the interior of the earth into three parts.
i) Crust – The outermost and solid part of the earth is the crust. Its thickness varies with regard to oceanic and continental areas. The average thickness of oceanic crust is 5 km while that of continental is around 30 km. In major mountainous regions, the continental crust is thicker.
ii) Mantle – The portion of the earth beyond the crust is called Mantle. It extends from Moho’s discontinuity to a depth of 2900 km. The upper portion of the mantle is called asthenosphere which is very weak. It extends up to 400 km and it stores the magma materials. The crust and the uppermost part of the mantle are together called as lithosphere. Its thickness ranges from 10-200 km.
iii) Core – The core is the innermost and central part of the earth. The core-mantle boundary is located at a depth of 2900 km. The outer core is in liquid state while the inner core is in solid state. The core is made up of very heavy materials like nickel and iron. So, it is also called as the Ni-Fe layer sometimes.
8. Explain different types of earthquakes.
The various types of earthquakes are –
a) Tectonic earthquake – In general, most earthquakes are tectonic. They occur due to sliding of rocks along a fault plane.
b) Volcanic earthquake – These are special kinds of tectonic earthquake. They remain confined to volcanic regions.
c) Collapse earthquake – In the areas of heavy mining activities, the overhead roofs collapse creating minor tremors. These are called as collapse earthquakes.
Some other forms of earthquake are – Reservoir Induced earthquake, Explosion earthquake, etc.
9. How can we measure magnitude and intensity of earthquake?
Magnitude is measured by Richter Scale and intensity is measured by Mercalli Scale.
10. Which one of the following seismic waves is the most disastrous?
a) P waves
b) Surface waves
c) S waves
11. Which one of the following gives direct information about the interior of the earth?
a) Earthquake waves b) Gravitational force c)Volcano d) Earth’s Magnetic field
12. Which type volcanic eruption have caused deccan trap formation?
a) Shield b) Flood c)Composite d)Caldera
13. Which one of the following describes the lithosphere?
a) Upper and lower mantle b) Crust and upper mantle c) Crust and core d) Mantle and core