Geography: UPSC Previous Year Questions (Prelims)

Explanation

Option (a) is correct: Earth has the highest average density among all planets in the Solar System. Earth has a metallic core rich in iron and nickel which makes it denser than gas giants like Jupiter or Saturn. Planet Density (g/cm3) Earth 5.51 Mercury 5.43 Venus 5.24 Mars 3.93 Jupiter 1.33 Saturn 0.69 Uranus 1.27 Neptune 1.64 Options (b), (c) and (d) are incorrect:

The most abundant element in Earth’s composition is iron (Fe), not silicon (Si). Earth’s elemental composition (by mass):

Iron(35%)>Oxygen(30%)>Silicon(15%) The Sun actually contains about 99.8% of the total mass of the Solar System, not just 75%. The remaining 0.2% of the mass is distributed among planets, moons, asteroids, and comets. The diameter of the Sun is 109 times and not 190 times that of Earth. Actual ratio of Sun’s diameter to Earth’s diameter:

Ratio = 1,391,000(Sun) × 12,742(Earth) 109 times

Explanation

Option (c) is correct: A sun halo is caused by the refraction of sunlight through ice crystals in cirrus clouds, forming a ring of light around the sun. This phenomenon occurs when light bends as it passes through the hexagonal ice crystals, creating a halo effect in the sky. The angle at which light is refracted by the ice crystals typically forms a halo with a radius of about 22 degrees, often appearing as a bright, circular ring. Sun halos are more common in colder regions and can be seen when thin cirrus clouds are present in the upper atmosphere. Options (a), (b) and (d) are incorrect:

Water vapor in stratus clouds: Stratus clouds are low-level clouds composed of water droplets, not ice crystals. Ice crystals in cirro-cumulus clouds: Cirro-cumulus clouds are not as common for halo formation as cirrus clouds. Dust particles in stratus clouds: Dust does not cause the refractive effects required for a halo.

Explanation

Statement 1 is incorrect: Equatorial regions generally experience two main seasons: a wet season (due to intense convectional rainfall) and a dry season (caused by a temporary shift in wind patterns). These regions do not have four distinct seasons like temperate zones.

Statement 2 is incorrect: In a Mediterranean climate, summers are dry due to the dominance of subtropical high-pressure systems, while winters are wet due to cyclonic activity. This climate is commonly found in areas like Southern California, parts of Australia, and the Mediterranean basin itself.

Statement 3 is correct: In China-type climate rainfall occurs throughout the year. This climate is known as the humid sub-tropical climate and is typical of regions like southern China, Taiwan, and parts of southeastern United States.

Statement 4 is correct: Tropical highlands show vertical zonation of climates, where altitude impacts temperature and vegetation. Example: In the Andes, conditions transition from tropical climates at lower elevations to temperate and alpine climates at higher altitudes. As the altitude increases, temperatures drop, and the climate changes from tropical conditions at the base to cooler temperate or even alpine climates at higher elevations.

Explanation

Albedo is the measure of a surface’s reflectivity, with higher albedo indicating greater reflection of sunlight.

Option (b) is correct: The correct sequence in decreasing order of albedo values is Tundra Taiga Tropical Deciduous Tropical Evergreen Tundra (Highest Albedo): Snow and ice dominate the Tundra landscape, leading to the highest reflectivity (albedo). Snow reflects up to 80-90% of sunlight. Taiga (Second Highest Albedo): Taiga, or boreal forests, have a lower albedo than tundra but still reflect sunlight during snowy winters. Dense coniferous forests, combined with snow, lead to moderate albedo values. Tropical Deciduous Forest - Moderate Albedo: These forests shed leaves seasonally, and during the dry season, the exposed ground and sparse canopy increase albedo slightly. Albedo ranges from 15% to 20%. Tropical Evergreen Forest - Low Albedo: Dense, evergreen canopies absorb most sunlight due to year-round leaf cover. Albedo is very low, around 10% to 15%.

Explanation

Assertion (A) is true: The 60°-65° latitudes in both hemispheres are dominated by the subpolar low-pressure belt, where the cold polar easterlies meet the warm westerlies, creating a zone of convergence. This leads to rising air and low-pressure conditions. Reason (R) is false: While oceans generally have a more stable pressure pattern due to their thermal inertia, low-pressure systems in the subpolar regions are not restricted to oceans and can also occur over land, especially in areas influenced by westerlies and cyclonic activity.

Explanation

A tropical cyclone is a powerful, rotating storm system characterized by strong winds, heavy rain, and low pressure, typically forming over warm ocean waters in tropical regions. Assertion (A) is true: In a tropical cyclone, surface winds spiral inwards toward the low-pressure center due to the Coriolis effect. The rotation direction depends on the hemisphere (counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere). Reason (R) is true: Air descends in the center of the cyclone, creating the eye of the storm, which is typically calm and free of rain. This descent is due to subsidence in the center of the low-pressure system. Reason (R) is NOT the correct explanation of Assertion (A):

The inward spiraling of surface winds is caused by the pressure gradient force pulling air toward the low-pressure center and the Coriolis effect, not by the descending air in the cyclone’s center.

Explanation

Thundercloud development, specifically cumulonimbus clouds, is influenced by various climatic and geographical factors.

Statement 1 is correct: Condensation is the process by which water vapor in the atmosphere cools and turns into liquid water droplets. For condensation to occur, the air must be saturated, and cooling must take place. This forms clouds, and in the case of thunderstorms, the towering cumulonimbus clouds. These clouds result from intense condensation when warm, moist air rises and cools.

Statement 2 is correct: High temperatures near the Earth’s surface heat the air, causing it to become lighter and rise (convection). Humidity refers to the amount of water vapor in the air. When the air is warm and moist, it carries more energy, which is essential for unstable atmospheric conditions. These conditions fuel the upward movement of air masses, leading to the formation of thunderclouds.

Statement 3 is correct: Orography refers to the influence of mountains and terrain on weather patterns. When air is forced to rise over mountains (called orographic lifting), it cools and condenses, forming clouds. This lifting mechanism often triggers thunderstorms, particularly on the windward sides of mountains where moisture-laden air ascends.

Statement 4 is correct: Vertical winds, or updrafts, are essential for the development of cumulonimbus clouds. These updrafts carry warm, moist air upward into the colder layers of the atmosphere, allowing the clouds to grow vertically. The combination of strong upward motion and moisture contributes to the towering structure of thunderclouds.

Explanation

Option (c) is correct: El Nino and Southern Oscillations (ENSO) events are known to significantly impact the Indian monsoon. During an El Niño event, sea surface temperatures in the central and eastern Pacific Ocean warm unusually. This disrupts global atmospheric circulation, including the monsoon winds. In India, this results in weakened monsoons and reduced rainfall, often leading to drought-like conditions in certain regions. The Southern Oscillation, a periodic change in atmospheric pressure between the western and eastern Pacific, works in tandem with El Niño to amplify its effects. Options (a), (b) and (d) are incorrect:

La Niña (cooler Pacific) typically strengthens the monsoon. Jet streams primarily influence monsoon onset and withdrawal, not occasional weak rainfall. Greenhouse effect, while contributing to long-term climate change, does not directly explain short-term monsoon variations.

Explanation

Statement 1 is incorrect: While some ocean currents are slow-moving others like the Gulf Stream, can move swiftly, reaching speeds of up to 5.6 miles per hour (9 kilometers per hour). Additionally, ocean currents are not limited to surface movements as there are also deep-water currents driven by differences in water density.

Statement 2 is correct: Ocean currents play a significant role in maintaining the Earth’s heat balance by transporting warm water from the equator to the poles and cold water from the poles to the equator. This helps regulate global temperatures.

Statement 3 is correct: Prevailing winds, such as the trade winds and westerlies, are a primary force driving ocean currents. These winds create friction on the ocean’s surface, causing water to move.

Statement 4 is correct: The configuration of the ocean, such as the shape of ocean basins, land masses, and coastlines, significantly influences the direction, speed, and path of ocean currents. For example, the Gulf Stream is influenced by the shape of the North American coastline, and the Antarctic Circumpolar Current is shaped by the absence of landmasses in the Southern Ocean.

Explanation

Below is a table summarizing approximate population figures for the four countries for the years 2002 and 2024:

Country Population (2002) Population (2024) Indonesia ~214 million ~283 million Brazil ~176 million ~212 million Russia ~145 million ~144 million Japan ~127 million ~123 million

Option (c) is correct: Based on the table above, the correct descending order (largest to smallest) for the population of the countries is: Indonesia (2)>Brazil (1)> Russia (4)> Japan (3)