UPSC CSE Prelims
Fundamentals of Geography Previous Year Questions (PYQs)

Detailed Explanation:

Correct Answer: ✅ Option 1 (I only)

Anadyr (Russia) and Nome (Alaska, USA) are located on opposite sides of the International Date Line (IDL). Although they are geographically close, crossing the IDL results in a change of calendar date. Therefore, people in these cities can experience the same part of the day but on different dates.

✅ Statement I is Correct: Anadyr and Nome are separated by the International Date Line, so they can have similar clock times but different calendar dates.

❌ Statement II is Incorrect: Anadyr is ahead of Nome. If it is Monday in Anadyr, it would still be Sunday in Nome, not Tuesday.

Short Notes: International Date Line (IDL)

• The International Date Line lies roughly along 180° longitude.

• Crossing the IDL from west to east subtracts one day.

• Crossing the IDL from east to west adds one day.

• The IDL is not perfectly straight; it bends to avoid splitting countries and island groups.

• Russia and Alaska are separated by the Bering Strait and the IDL.

• Places close to each other geographically can have different calendar dates due to the IDL.

• The IDL is important for global travel, communication, and timekeeping.

Detailed Explanation:

Correct Answer: ✅ Option 2 (Only Four)

When counting all official time zones, including overseas territories and external territories, the United Kingdom, Denmark, New Zealand, and Australia each have more than four time zones. Brazil, however, has exactly four time zones, not more than four.

✅ Statement I: United Kingdom – Correct

• The UK has 9 time zones when overseas territories are included.

• Territories such as the Falkland Islands, Gibraltar, Bermuda, and Pitcairn Islands contribute to multiple time zones.

✅ Statement II: Denmark – Correct

• Denmark has more than four time zones due to Greenland and the Faroe Islands.

• Greenland alone spans several time zones.

✅ Statement III: New Zealand – Correct

• New Zealand has 5 time zones when including territories such as the Chatham Islands, Tokelau, and the Ross Dependency (Antarctica).

✅ Statement IV: Australia – Correct

• Australia has 8–9 time zones when all external territories are counted.

• These include territories such as Norfolk Island, Christmas Island, and Cocos (Keeling) Islands.

❌ Statement V: Brazil – Incorrect

• Brazil officially has 4 time zones, not more than four.

Short Notes: World Time Zones

• The Earth is divided into 24 standard time zones.

• Each time zone generally covers 15° of longitude.

• Countries with large territories often have multiple time zones.

• Russia has the highest number of time zones (11).

• France has the most time zones globally (12) when overseas territories are included.

• Overseas territories significantly increase the number of time zones for some countries.

• India follows a single time zone: IST (UTC +5:30).

Detailed Explanation:

Scientific studies confirm that the Earth's rotational axis is gradually shifting, a phenomenon known as polar drift. Melting polar ice redistributes mass from the poles toward the equator, changing the Earth's moment of inertia and affecting its rotation. Solar flares and CMEs do impact the upper atmosphere, but they do not significantly alter the Earth's rotational axis.

✅ Statement I is Correct: Satellite observations show that Earth's rotational axis is drifting and its rotation rate is changing slightly.

✅ Statement II is Correct: Solar flares and CMEs transfer large amounts of energy to the thermosphere and magnetosphere.

✅ Statement III is Correct: Melted polar ice redistributes water toward lower latitudes, especially near the equator.

❌ Statement II does NOT explain Statement I: Solar activity affects the atmosphere and satellites but not the Earth's rotational axis significantly.

✅ Statement III explains Statement I: Redistribution of mass from poles to equator changes Earth's moment of inertia, causing polar drift and slight rotational changes.

Concept Note:

Moment of Inertia is the resistance of a rotating object to changes in its rotation. When mass moves away from the rotational axis (toward the equator), the moment of inertia increases, leading to changes in rotational speed and axis orientation.

Detailed Explanation:

Answer: Option 3 — Both 1 and 2

The Coriolis force is an apparent deflection force caused by Earth's rotation, affecting moving objects including wind and ocean currents. Both statements about the Coriolis force are correct based on fundamental principles of atmospheric and oceanographic dynamics.

✅ Statement 1 – Correct: The Coriolis force is directly proportional to the velocity of the moving object (F = 2mΩv sinφ), so higher wind velocity results in greater Coriolis force and deflection.

✅ Statement 2 – Correct: The Coriolis force varies with the sine of latitude (sinφ), being maximum at the poles (sin 90° = 1) and zero at the equator (sin 0° = 0), where no deflection occurs.

📝 Short Notes: Coriolis Force

• Definition: An apparent deflection force acting on moving objects due to Earth's rotation, named after French scientist Gaspard-Gustave de Coriolis.
• Mathematical Expression: F = 2mΩv sinφ, where m = mass, Ω = Earth's angular velocity, v = object velocity, φ = latitude.
• Direction of Deflection: Objects are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
• Latitudinal Variation: Zero at the equator, increases with latitude, and maximum at the poles; this explains why tropical cyclones do not form within 5° of the equator.
• Dependency on Velocity: Greater the speed of the moving object (wind, ocean current, missile), greater the Coriolis deflection.
• Impact on Wind Patterns: Responsible for the rotation of cyclones, anticyclones, trade winds deflection, and the geostrophic wind balance.
• Ocean Currents: Causes major ocean currents to flow in circular patterns (gyres) - clockwise in Northern Hemisphere and counterclockwise in Southern Hemisphere.
• Practical Applications: Critical for long-range artillery, missile trajectories, aviation routes, and understanding global circulation patterns.

Detailed Explanation:

Answer: Option 4 — 2 and 4

On June 21, the Summer Solstice in the Northern Hemisphere, the sun's rays are directly overhead at the Tropic of Cancer, and all latitudes north of the Equator experience daylight longer than 12 hours. The Arctic Circle experiences 24 hours of continuous daylight (Midnight Sun), while the Equator always has exactly 12 hours of daylight throughout the year.

✅ Statement 1 (Equator) – Incorrect: The Equator experiences exactly 12 hours of daylight on all days of the year, not more than 12 hours.
✅ Statement 2 (Tropic of Cancer) – Correct: On June 21, the Tropic of Cancer receives direct sunlight and experiences more than 12 hours of daylight.
❌ Statement 3 (Tropic of Capricorn) – Incorrect: The Tropic of Capricorn lies in the Southern Hemisphere, which is tilted away from the Sun on June 21, resulting in less than 12 hours of daylight.
✅ Statement 4 (Arctic Circle) – Correct: The Arctic Circle experiences 24 hours of continuous daylight on June 21, known as the Midnight Sun phenomenon.

📝 Short Notes: Summer Solstice and Day Length

• Summer Solstice (June 21): The Northern Hemisphere is tilted at its maximum (23.5°) toward the Sun, resulting in the longest day of the year in the Northern Hemisphere.
• Direct Rays at Tropic of Cancer: On this day, the sun's rays fall vertically at the Tropic of Cancer (23.5° N), which receives maximum solar energy.
• Day Length Pattern: All latitudes north of the Equator experience more than 12 hours of daylight on June 21, with day length increasing toward the North Pole.
• Equator: The Equator experiences exactly 12 hours of daylight and 12 hours of night on all days of the year due to its position midway between the poles.
• Midnight Sun: At the Arctic Circle (66.5° N) and all latitudes beyond it toward the North Pole, the sun does not set on June 21, resulting in 24 hours of continuous daylight.
• Southern Hemisphere: On June 21 (Winter Solstice in Southern Hemisphere), all latitudes south of the Equator experience less than 12 hours of daylight, with the Antarctic Circle experiencing 24 hours of darkness.
• Tropic of Capricorn: Located at 23.5° S, it experiences its shortest day on June 21 with significantly less than 12 hours of daylight.

Detailed Explanation:

Correct Answer: ✅ Option 4 (Statement-I is incorrect, but Statement-II is correct)

Stars live for different lengths of time depending mainly on how fast they consume their nuclear fuel. Although giant stars contain more fuel, they burn it much more rapidly than dwarf stars.

❌ Statement I is Incorrect: Giant stars do not live longer than dwarf stars. Due to their high energy output, they exhaust their fuel quickly and have shorter lifespans.

✅ Statement II is Correct: Giant stars have much higher core temperatures and pressures, leading to a faster rate of nuclear fusion reactions than dwarf stars.

Relationship: Statement II actually explains why Statement I is incorrect. Faster nuclear reactions mean faster fuel consumption, resulting in a shorter lifespan.

Short Notes: Stellar Life Cycle

• The lifespan of a star depends mainly on its mass.

• More massive stars have higher core temperatures and faster fusion rates.

• Giant stars burn fuel much faster and may live only millions of years.

• Small dwarf stars can survive for billions to trillions of years.

• The Sun is a medium-sized star with an expected lifespan of about 10 billion years.

• Red dwarfs are the longest-living stars in the universe.

• Stars generate energy through nuclear fusion, mainly converting hydrogen into helium.

• After exhausting fuel, stars evolve into white dwarfs, neutron stars, or black holes depending on their mass.

Detailed Explanation:

Answer: Option 2 — Second half of the month of June

The longest day of the year in the northern hemisphere is known as the summer solstice, which typically occurs on June 20th or 21st, falling in the second half of June. On this day, the sun is directly overhead at the Tropic of Cancer (23.5°N latitude), resulting in maximum daylight hours in the northern hemisphere. The exact date may vary slightly from year to year due to the calendar system and Earth's orbital mechanics.

📝 Short Notes: Solstices and Equinoxes

• During solstices, the sun is directly overhead at either the Tropic of Cancer (June) or Tropic of Capricorn (December)
• During equinoxes, the sun is directly overhead at the Equator, resulting in equal day and night globally
• The tilt of Earth's axis (23.5°) is responsible for seasonal variations and solstices
• The term 'solstice' comes from Latin 'sol' (sun) and 'sistere' (to stand still), as the sun appears to pause at its northernmost or southernmost position

Detailed Explanation:

Answer: Option 1 — does not set below the horizon at the Arctic Circle

On 21st June, the Northern Hemisphere experiences the Summer Solstice, when the North Pole is tilted at its maximum angle (23.5°) towards the Sun. This results in the Arctic Circle (66.5°N) experiencing 24 hours of continuous daylight, meaning the Sun does not set below the horizon. Conversely, the Antarctic Circle experiences polar night, the Equator has equal day and night, and the Sun is directly overhead at the Tropic of Cancer (not Capricorn).

📝 Short Notes: Solstices and Sun's Position

• Arctic Circle: Located at 66.5°N latitude; experiences midnight sun during summer solstice
• Antarctic Circle: Located at 66.5°S latitude; experiences midnight sun during winter solstice (December)
• Tropic of Cancer: 23.5°N - Sun directly overhead on 21st June
• Tropic of Capricorn: 23.5°S - Sun directly overhead on 22nd December
• Earth's axial tilt: 23.5° from perpendicular to orbital plane causes seasonal variations

Detailed Explanation:

Answer: Option 1 — Bengaluru

Delhi is located at approximately 77.10°E longitude, and among the given options, Bengaluru (77.59°E) lies closest to this longitude with a difference of only about 0.49°. Hyderabad (78.49°E), Nagpur (79.09°E), and Pune (73.86°E) are all farther away from Delhi's longitude.

📝 Short Notes: Longitudes of Major Indian Cities

• Bengaluru and Delhi nearly share the same longitudinal line, making them closest in east-west positioning.
• Pune lies significantly west of Delhi, while Hyderabad and Nagpur lie progressively east.
• Understanding longitude positions helps in determining time zones and relative geographical positioning of cities.

Detailed Explanation:

Answer: Option 3 — 1 and 3 only

This question tests knowledge about Earth's magnetic field reversals and the evolution of Earth's atmosphere. Statements 1 and 3 are scientifically accurate, while Statement 2 contains factual errors about the early Earth's atmospheric composition.

✅ Statement 1 – Correct: The Earth's magnetic field undergoes geomagnetic reversals approximately every few hundred thousand years, a phenomenon recorded in volcanic rocks and ocean floor sediments.

❌ Statement 2 – Incorrect: The early Earth's atmosphere (over 4 billion years ago) had virtually no free oxygen and was dominated by carbon dioxide, water vapor, nitrogen, and methane—not 54% oxygen.

✅ Statement 3 – Correct: Living organisms, particularly cyanobacteria through photosynthesis during the Great Oxygenation Event (~2.4 billion years ago), fundamentally transformed Earth's atmosphere by adding oxygen.

📝 Short Notes: Earth's Atmospheric Evolution

• Primordial Atmosphere: Early Earth (4+ billion years ago) had no free oxygen; atmosphere consisted mainly of hydrogen, helium, water vapor, methane, ammonia, and carbon dioxide.
• Secondary Atmosphere: Formed through volcanic outgassing, releasing CO₂, nitrogen, water vapor, and sulfur compounds.
• Great Oxygenation Event (GOE): Around 2.4 billion years ago, cyanobacteria began photosynthesis, gradually increasing atmospheric oxygen from ~0% to ~21% today.
• Geomagnetic Reversals: Earth's magnetic poles switch positions irregularly; last reversal occurred ~780,000 years ago (Brunhes-Matuyama reversal).
• Evidence of Reversals: Preserved in magnetized minerals in volcanic rocks (paleomagnetism) and oceanic crust spreading from mid-ocean ridges.
• Impact on Life: The oxygen revolution caused mass extinction of anaerobic organisms but enabled evolution of complex aerobic life forms.

Detailed Explanation:

Seasonal variation in day and night length occurs due to the Earth's revolution around the Sun combined with its axial tilt of 23.5°.

The tilted axis causes different hemispheres to receive varying amounts of direct sunlight throughout the year – when the Northern Hemisphere is tilted toward the Sun (summer solstice), it experiences longer days; when tilted away (winter solstice), it experiences shorter days.

❌ Option 1 – Incorrect: Earth's rotation causes the daily cycle of day and night (24 hours), not seasonal variation in their length.

❌ Option 3 – Incorrect: Latitudinal position determines the magnitude of variation (polar regions experience extreme variation, equatorial regions minimal), but not the cause of seasonal changes.

❌ Option 4 – Incorrect: The elliptical orbit affects Earth-Sun distance but does not cause seasonal day-length variation; the tilt is the primary factor.

Detailed Explanation:

Polaris (Pole Star) is always located in the northern direction in the Northern Hemisphere.

To walk east, a person must face east with north on the left side; therefore, keeping the Pole Star to the left ensures eastward movement.

Detailed Explanation:

Carbon, Hydrogen, and Nitrogen are the primary elements responsible for the origin of life on Earth.

Carbon forms the backbone of all organic molecules, while Hydrogen and Nitrogen are essential for creating amino acids, nucleic acids (DNA/RNA), and proteins — the fundamental building blocks of life.

Detailed Explanation:

Earth's magnetic field (magnetosphere) acts as a protective shield, deflecting charged particles (solar wind, cosmic rays) toward the polar regions.

When these particles collide with atmospheric gases near the poles, they create auroras (Aurora Borealis and Aurora Australis), preventing direct surface exposure that would harm living organisms.