NCERT Solutions Class 11 Geography Chapter 3: Interior of the Earth– This article includes free NCERT Solutions Class 11 Geography Chapter 3: Interior of the Earth according to the latest CBSE Syllabus 2023-24, and guidelines.
It has been developed by the subject matter experts at GFG, to help the students of Class 11 create a solid conceptual base for NCERT Solutions Class 11 Geography Chapter 3: Interior of the Earth and help them solve questions for exams.
NCERT Solutions Class 11 Geography Chapter 3: Interior of the Earth
Page No: 29
1. Multiple choice questions.
(i) Which one of the following earthquake waves is more destructive?
(a) P-waves
(b) S-waves
(c) Surface waves
(d) None of the above
Answer:
(a) P-waves
(ii) Which one of the following is a direct source of information about the interior of the earth?
(a) Earthquake waves
(b) Volcanoes
(c) Gravitational force
(d) Earth magnetism
Answer:
(a) Earthquake waves
(iii) Which type of volcanic eruptions have caused Deccan Trap formations?
(a) Shield
(b) Flood
(c) Composite
(d) Caldera
Answer:
(b) Flood
(iv) 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
Answer:
(b) crust and upper mantle
2. Answer the following questions in about 30 words.
(i) What are body waves?
Answer:
Body waves are generated due to the release of energy at the focus and move in all directions travelling through the body of the earth. These are of two types: P-waves and S-waves.
(ii) Name the direct sources of information about the interior of the earth.
Answer:
The direct sources of information about the interior of the earth are:
Mining: The extraction of valuable minerals from the Earth constitutes mining. Surface rock and materials obtained from mining sites represent the most readily accessible solid earth resources.
Drilling: Scientists are engaged in significant drilling initiatives such as the “Deep Ocean Drilling Project” and the “Integrated Ocean Drilling Project.” These, alongside numerous other deep drilling endeavors, have yielded substantial volumes of data by analyzing materials collected from various depths.
Volcanic eruption: Volcanic eruptions offer another source of obtaining direct information. When molten material (magma) is ejected onto the Earth’s surface during volcanic events, it becomes available for laboratory analysis, providing valuable insights.
(iii) Why do earthquake waves develop shadow zone?
Answer:
When earthquake waves travel, they get picked up by seismographs placed far away. But sometimes, there are places where the waves don’t show up on the seismographs. We call these areas the ‘shadow zone’. Each earthquake has its own shadow zone.
Scientists found out that seismographs within 105° from the earthquake’s center can detect both P and S-waves. But if they’re placed beyond 145°, they only catch P-waves, not S-waves. So, between 105° and 145° from the center, there’s a shadow zone for both types of waves. This zone beyond 105° doesn’t get any S-waves at all.
The shadow zone for S-waves is bigger than for P-waves. The P-wave shadow zone looks like a band around the Earth between 105° and 145° from the center. But the S-wave shadow zone covers over 40% of the Earth’s surface and is much wider.
(iv) Briefly explain the indirect sources of information of the interior of the earth other than those of seismic activity.
Answer:
The indirect sources of information of the interior of the earth are:
Temperature, Pressure, and Density: These factors increase as you go deeper into the Earth from its surface. Scientists have calculated the rate at which temperature, pressure, and density change. By knowing the Earth’s total thickness, they can estimate these values at various depths.
Meteors: Although meteors don’t come from inside the Earth, their material and structure resemble that of our planet. This similarity makes meteors another source of information about Earth’s interior.
Gravitational Force: Gravity is stronger near the poles and weaker at the equator. Gravity values also vary depending on the amount of material. The uneven distribution of material within the Earth affects these values.
Magnetic Field: Magnetic surveys reveal the distribution of magnetic materials in the Earth’s crust, providing insights into the distribution of materials in this region.
3. Answer the following questions in about 150 words.
(i) What are the effects of propagation of earthquake waves on the rock mass through which they travel?
Answer:
Earthquake waves come in two main types: body waves and surface waves. Body waves originate from energy released at the earthquake focus and travel through the Earth’s interior in all directions, hence their name.
These waves interact with surface rocks, generating another set of waves known as surface waves, which move along the Earth’s surface.
The speed of waves changes as they pass through materials with different densities, with denser materials causing faster wave velocities.
P-waves vibrate parallel to the direction of the wave. This exerts pressure on the material in the direction of the propagation. As a result, it creates density differences in the material leading to stretching and squeezing of the material.
S-waves vibrate perpendicular to their direction of travel in the vertical plane, creating troughs and crests in the material they pass through. Surface waves are considered the most destructive.
Seismographs located within 105° from the earthquake’s epicenter detect both P and S-waves, while those beyond 145° only register P-waves, not S-waves. Therefore, a zone between 105° and 145° from the epicenter is termed the shadow zone for both types of waves. The area beyond 105° does not receive S-waves at all. The shadow zone for S-waves is larger than for P-waves, covering over 40% of the Earth’s surface.
(ii) What do you understand by intrusive forms? Briefly describe various intrusive forms.
Answer:
The lava that is released during volcanic eruptions on cooling develops into igneous rocks. These forms are called intrusive forms.
Various intrusive forms are:
Batholiths: These are immense bodies of magma that cool deep within the Earth’s crust, forming large domes. They represent the solidified sections of magma chambers.
Lacoliths: Lacoliths are expansive dome-shaped intrusive formations with a flat base, connected below by a pipe-like conduit. They resemble the surface features of composite volcanoes but are situated at deeper levels.
Lapolith: When lava ascends and encounters a weak plane, it may spread horizontally and settle in various shapes. If it forms a concave saucer-like body facing the sky, it’s termed a lapolith.
Phacolith: A sinuous mass of intrusive rocks positioned near the crest of an anticline or the base of a syncline.
Sills: These are nearly horizontal bodies of intrusive igneous rock. Depending on their thickness, they are termed either sheets (thin deposits) or sills (thick horizontal formations).
Dykes: Dykes form when lava flows through fractures and fissures in the Earth’s crust, solidifying vertically from ground level. Once cooled, they create wall-like structures perpendicular to the surface.
Conclusion
In this article, we provided free NCERT Solutions for NCERT Solutions Class 11 Geography Chapter 3: Interior of the Earth, adhering to the latest CBSE syllabus for 2023-24. Understanding the interior of the Earth is crucial for comprehending various geological processes and phenomena. Through seismic activity, direct sources like earthquake waves provide valuable insights into the Earth’s composition and structure.
Chapter 3: Interior of the Earth- FAQs
What makes P-waves more destructive than S-waves in earthquakes?
P-waves are more destructive than S-waves in earthquakes because they have a higher velocity and can travel through both solid and liquid layers of the Earth. This allows them to cause more damage as they can propagate through a wider range of materials compared to S-waves.
How do seismographs help identify the shadow zone in earthquake waves?
Seismographs help identify the shadow zone in earthquake waves by recording the arrival times and types of waves at different distances from the earthquake’s epicenter. Seismographs within 105° from the epicenter detect both P and S-waves, while those beyond 145° only register P-waves, indicating a shadow zone for S-waves between these distances.
Besides seismic activity, what other methods provide information about the Earth’s interior?
Besides seismic activity, other methods providing information about the Earth’s interior include temperature, pressure, and density measurements, analysis of meteors, gravitational force variations, and magnetic field surveys.
What are the effects of earthquake waves on the rock mass they traverse?
The effects of earthquake waves on the rock mass they traverse include stretching and squeezing of the material due to pressure from P-waves, and the creation of troughs and crests in the material by S-waves. Surface waves, which are the most destructive, cause significant damage to structures and landscapes.
What are the various intrusive forms found within the Earth’s crust?
Intrusive forms found within the Earth’s crust include batholiths, lacoliths, lapoliths, phacoliths, sills, and dykes. These formations provide valuable insights into the geological processes and history of the Earth’s interior.