UPSC Prelims 2011 Q27: Geography – Atmosphere & Climatology
A layer in the Earth’s atmosphere called Ionosphere facilitates radio communication. Why?
1. The presence of ozone causes the reflection of radio waves to Earth.
2. Radio waves have a very long wavelength.
Which of the statements given above is/are correct?
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer: (d) Neither 1 nor 2
Explanation
Why the ionosphere helps radio communication
The ionosphere is a layer of the upper atmosphere containing charged particles (ions and free electrons), created by solar radiation ionising gas molecules.
| Statement | Verdict | Reason |
|---|---|---|
| 1. Presence of ozone causes reflection of radio waves | Incorrect | Ozone is in the stratosphere and absorbs UV radiation; radio-wave reflection is caused by free electrons/ions, not ozone |
| 2. Radio waves have a very long wavelength | Incorrect | Only certain frequency bands reflect off the ionosphere; wavelength alone does not explain the mechanism, and not all radio waves behave this way |
The real mechanism:
| Point | Detail |
|---|---|
| What reflects radio waves | Ionised layers (charged particles) bending/reflecting certain frequencies back to Earth |
| Why it helps communication | Lets radio signals bounce over long distances beyond the horizon |
| Ozone's actual role | Absorbs UV radiation, protecting life; unrelated to radio reflection |
Answer: (d) Neither 1 nor 2.
Why each option is right or wrong
- (a) Incorrect. Ozone is not responsible for radio-wave reflection; ionisation is.
- (b) Incorrect. Wavelength alone does not explain the reflection mechanism.
- (c) Incorrect. Neither statement correctly explains the ionosphere's role, so 'both' is wrong.
- (d) CORRECT. Neither the presence of ozone nor long wavelength explains why the ionosphere reflects radio waves; it is ionisation (charged particles).
Key point
Ionosphere reflects radio waves because of its charged particles (ions/free electrons) from solar radiation, NOT because of ozone or wavelength.
Remember
Ionosphere reflects radio waves due to ionisation, not ozone.
Common mistakes
- Confusing the ozone layer (stratosphere, blocks UV) with the ionosphere (reflects radio waves).
- Thinking wavelength by itself is the deciding factor, rather than the layer's ionised state.
- Assuming any 'layer of the atmosphere' statement involving ozone must be correct.
Exam tip
Ozone = UV protection in the stratosphere. Ionosphere = charged particles reflecting radio waves. Keep the two separate.
Sources
- NCERT Class XI Geography — Fundamentals of Physical Geography — Composition and Structure of Atmosphere
- Savindra Singh — Climatology (Prayag Pustak Bhawan)