UPSC Prelims 2011 · Question 97 of 100

UPSC Prelims 2011 question on Ionosphere Radio Communication

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?

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2
Show answer

Answer: D. Neither 1 nor 2

Verdict

Correct Answer: Neither 1 nor 2

Both statements are incorrect because ionospheric radio communication is due to ionised particles and frequency-based reflection, not ozone or merely long wavelength.

Analysis

The ionosphere helps in radio communication because it contains ionised particles that can reflect certain radio waves back to Earth. It is not due to ozone.

Statement by statement

1. Presence of ozone causes reflection of radio waves — Incorrect

Ozone is mainly found in the stratosphere, not the ionosphere.

The ionosphere reflects radio waves because it contains ions and free electrons produced by solar radiation.

2. Radio waves have a very long wavelength — Incorrect

Reflection by the ionosphere depends mainly on frequency, not simply on very long wavelength.

High-frequency shortwave radio waves are commonly reflected by the ionosphere, while VHF and UHF waves generally pass through it.

Extra UPSC info

* Ionosphere extends roughly from about 80 km to 400 km above Earth.

* It contains ionised gases formed due to solar radiation.

* Ozone layer is mainly in the stratosphere, around 15–35 km altitude.

* Ionospheric reflection enables long-distance radio communication beyond the horizon.

* Skywave propagation means radio waves are reflected back to Earth by the ionosphere.

* Do not confuse ozone’s UV absorption role with ionosphere’s radio wave reflection role.

More questions on Information and Communication Technology

All 36 questions on Information and Communication Technology →

← Full 2011 question paper · All Science and Technology questions