UPSC Prelims 2012 Q20: Science & Technology – Space Technology & Astronomy
Electrically charged particles from space travelling at speeds of several hundred km/sec can
severely harm living beings if they reach the surface of the Earth. What prevents them from
reaching the surface of the Earth ?
- (a) The Earth's magnetic field diverts them towards its poles
- (b) Ozone layer around the Earth reflects them back to outer space
- (c) Moisture in the upper layers of atmosphere prevents them from reaching the surface of the Earth
- (d) None of the statements (a), (b) and (c) given above is correct
Answer: (a) The Earth's magnetic field diverts them towards its poles
Explanation
What stops charged particles from space?
The Sun throws out a stream of charged particles called the solar wind.
The Earth's magnetic field (the magnetosphere) deflects them and guides them towards the poles.
| Option | Verdict | Reason |
|---|---|---|
| (a) The Earth's magnetic field diverts them towards its poles | Correct | Charged particles follow magnetic field lines |
| (b) Ozone layer reflects them back to outer space | Incorrect | Ozone absorbs ultraviolet light; it does not stop charged particles |
| (c) Moisture in the upper atmosphere prevents them | Incorrect | Not the cause |
| (d) None of the above | Incorrect | Option (a) is right |
Related features:
| Feature | Detail |
|---|---|
| Van Allen belts | Zones where the field traps charged particles |
| Aurora Borealis and Australis | Glow near the poles when particles hit the upper air |
| Solar storms | Can disturb satellites, radio and power grids |
Answer: (a) The Earth's magnetic field diverts them towards its poles.
Why each option is right or wrong
- (a) CORRECT. The Earth's magnetic field diverts charged particles towards the poles.
- (b) Incorrect. The ozone layer blocks ultraviolet rays, not charged particles.
- (c) Incorrect. Moisture in the upper atmosphere does not stop them.
- (d) Incorrect. Option (a) gives the right reason.
Key point
Magnetosphere deflects the solar wind; Van Allen belts trap particles; auroras appear near the poles. Ozone blocks UV, not charged particles.
Remember
Magnetic field shields us from charged particles.
Common mistakes
- Giving the ozone layer every protective role.
- Not linking auroras to charged particles at the poles.
- Confusing radiation (UV) with charged particles.
Exam tip
Ozone stops rays; the magnetic field stops charged particles.
Sources
- NCERT Class XII — Physics Part I (Moving Charges and Magnetism; Magnetism and Matter: Earth's magnetism)
- NASA — Earth's magnetosphere and the Van Allen belts