UPSC Prelims 2013 Q18: Geography – Physical Geography & Geomorphology
Consider the following:
1. Electromagnetic radiation
2. Geothermal energy
3. Gravitational force
4. Plate movements
5. Rotation of the earth
6. Revolution of the earth
Which of the above are responsible for bringing dynamic changes on the surface of the earth?
- (a) 1, 2, 3 and 4 only
- (b) 1, 3, 5 and 6 only
- (c) 2, 4, 5 and 6 only
- (d) 1, 2, 3, 4, 5 and 6
Answer: (d) 1, 2, 3, 4, 5 and 6
Explanation
Forces that change the surface of the Earth
| Factor | Brings dynamic change? | How |
|---|---|---|
| 1. Electromagnetic radiation | Yes | Sunlight drives weather, weathering and erosion |
| 2. Geothermal energy | Yes | Heat from inside drives volcanoes and plate movement |
| 3. Gravitational force | Yes | Moves water, ice and rock downhill; causes tides |
| 4. Plate movements | Yes | Build mountains; cause earthquakes |
| 5. Rotation of the earth | Yes | Causes the Coriolis force, day and night, and tidal rhythm |
| 6. Revolution of the earth | Yes | Causes seasons |
Two families of forces:
| Type | Examples |
|---|---|
| Endogenic (internal) | Geothermal energy, plate movements, volcanism |
| Exogenic (external) | Sunlight, gravity, wind, water, ice |
Answer: (d) 1, 2, 3, 4, 5 and 6.
Why each option is right or wrong
- (a) Incorrect. Rotation and revolution of the Earth also bring changes.
- (b) Incorrect. Geothermal energy and plate movements also bring changes.
- (c) Incorrect. Electromagnetic radiation and gravity also bring changes.
- (d) CORRECT. All six factors bring dynamic changes on the surface of the Earth.
Key point
Earth's surface is shaped by endogenic forces (geothermal energy, plate movements) and exogenic forces (solar radiation, gravity), plus rotation and revolution.
Remember
All six shape the Earth's surface.
Common mistakes
- Leaving out electromagnetic radiation, which is simply sunlight.
- Thinking rotation and revolution affect only time and seasons.
- Forgetting gravity as the force behind all downhill movement.
Exam tip
A long list of natural forces is usually all correct.
Sources
- NCERT Class XI — Fundamentals of Physical Geography, Ch 6 (Geomorphic Processes)
- NCERT Class XI — Fundamentals of Physical Geography, Ch 3 (Interior of the Earth)