Weekly Revision Test : January 31st, 2021

The earth’s radius is 6,370 km. No one can reach the centre of the earth and make observations or collect samples of the material.  

• Most of our knowledge about the interior of the earth is largely based on estimates and inferences. Yet, a part of the information is obtained through direct observations and analysis of materials. 
• Volcanic eruption forms another source of obtaining direct information. As and when the molten material (magma) is thrown onto the surface of the earth, during volcanic eruption it becomes available for laboratory analysis. However, it is difficult to ascertain the depth of the source of such magma.  
• Indirect Sources: Another source of information is the meteors that at times reach the earth. However, it may be noted that the material that becomes available for analysis from meteors, is not from the interior of the earth.  

• The material and the structure observed in the meteors are similar to that of the earth. They are solid bodies developed out of materials same as, or similar to, our planet.  
• Hence, this becomes yet another source of information about the interior of the earth.  
• The other indirect sources include gravitation, magnetic field, and seismic activity. 

Source: NCERT – XI Fundamentals of Physical Geography 

The portion of the interior beyond the crust is called the mantle. The mantle extends from Moho’s discontinuity to a depth of 2,900 km. The upper portion of the mantle is called asthenosphere.  

• Connardo’s discontinuity separates upper felsic layer of continent from mefic layer. It is only present within continental crust and not in the oceanic layer. 
• While the Gutenberg discontinuity separates the lower mantle from the core. It is present at about 2900 km of depth. 

Source: NCERT – XI Fundamentals of Physical Geography 

Moon is a non-luminous object because as we know that luminous objects emit light on their own while non-luminous objects emit light with the help of luminous objects. 

Here sun is a luminous object so moon takes light from the sun and emits light in our surrounding and our environment. 

Source: G C Leong 

Sonoran Desert, also called Desierto de Altar, arid region covering 120,000 square miles (310,800 square km) in southwestern Arizona and southeastern California, U.S., and including much of the Mexican state of Baja California Sur, part of Baja California State, and the western half of the state of Sonora.  

Subdivisions of the hot, dry region include the Colorado and Yuma deserts. 

Source: G C Leong 

India has 15,106.7 Km of land border and a coastline of 7,516.6 Km including island territories. The length of our land borders with neighboring countries is as under:  

Source: NCERT – XI Fundamentals of Physical Geography 

The climate of India is described as a monsoon type. This type of climate is found in south and south-east Asia. However, there are variations in climatic conditions in the country itself. The coastal regions of India show the least amount of difference between the temperatures of night and day. In the interior regions, the difference in temperatures of day and night is huge. 

The climate of India depends greatly on monsoon winds. The monsoons usually happen due to the differential heating of land and water. 

• The Advancing Monsoon (Rainy Season) or South west Monsoon: By early June, the trade winds of the southern winds bring abundant moisture to the country. The windward side of the Western Ghats receives very heavy rainfall, more than 250 cm. The monsoon is known for its uncertainties. While it causes heavy floods in one part, it may be responsible for droughts in the other. It is also irregular in arrival and retreat. 
• Retreating Monsoons (Transition Season) or North-east Monsoon: During October-November, the monsoons become weaker. The sun moves towards the south. By the beginning of October, monsoon withdraws from the Northern Plains. There is a transition from hot rainy season to dry winter season. 

Source: NCERT – XI India Physical Environment 

Sikkim and Meghalaya are the only two states in India to share border with just one state. Sikkim shares border with West Bengal while Meghalaya shares border with Assam. 

• Uttar Pradesh is the only state which has maximum number of neighboring state. Uttar Pradesh shares border with 9 states, which are Uttarakhand, HP, Delhi, Haryana, Rajasthan, MP, Chhattisgarh, Bihar and Jharkhand. 
• The second highest number of neighboring states is 7. Both Assam and Chhattisgarh shares border with 7 other states. 

Source: NCERT – XI India Physical Environment 

Guru Shikar is located at a height of 1772 meters above sea level. This mountain peak is located at a distance of 15 km from Mount Abu in the Aravalli range. It is the highest peak in the Aravali Range. 

Source: NCERT – XI India Physical Environment 

India’s climate is controlled by a number of factors which can be broadly divided into two groups — factors related to location and relief, and factors related to air pressure and winds. With a long coastline, large coastal areas have an equable climate.  

• Areas in the interior of India are far away from the moderating influence of the sea. Such areas have extremes of climate.  
• That is why the people of Mumbai and the Konkan coast have hardly any idea of extremes of temperature and the seasonal rhythm of weather.  
• On the other hand, the seasonal contrasts in weather at places in the interior of the country such as Delhi, Kanpur and Amritsar affect the entire sphere of life. 

Source: NCERT – XI India Physical Environment 

India is a vast country. Lying entirely in the Northern hemisphere the main land extends between latitudes 8°4’N and 37°6’N and longitudes 68°7’E and 97°25’E.  

• The Tropic of Cancer (23° 30’N) divides the country into almost two equal parts. To the southeast and southwest of the mainland, lie the Andaman and Nicobar Islands and the Lakshadweep islands in Bay of Bengal and Arabian Sea respectively.  

• The land mass of India has an area of 3.28 million square km. India’s total area accounts for about 2.4 per cent of the total geographical area of the world. It is clear that India is the seventh largest country of the world.  
• India has a land boundary of about 15,200 km and the total length of the coast line of the mainland including Andaman and Nicobar and Lakshadweep is 7,516.6 km. 

Source: NCERT – XI India Physical Environment