Question

The propagation of radio signals is greatly influenced by

• A. Troposphere
• B. Ionosphere
• C. Exosphere
• D. Thermosphere

Hint:

Match the word "ionosphere" with "ions", the charged particles that bounce radio waves back down to Earth.

Answer 1

The Correct Option is B

This is a basic physical geography question about the Earth's atmosphere, and it helps to think about what property a layer needs to interact with radio waves.

1. Troposphere: This is the layer closest to the ground, where clouds form and weather happens, but it does not contain the charged particles needed to bounce radio waves back to Earth.
2. Ionosphere: Correct. This layer is ionised by the Sun's radiation, giving it free electrons and ions that reflect radio waves, especially shortwave signals, allowing them to travel around the curve of the Earth rather than shooting off into space.
3. Exosphere: This is the outermost fringe of the atmosphere, so thin that it barely counts as air; it has no meaningful effect on radio signals.
4. Thermosphere: While the ionosphere physically sits within the thermosphere's altitude range, the radio-reflecting property comes specifically from ionisation, which is why the ionosphere gets credit for this effect rather than the thermosphere as a whole.

The key idea to remember is the word "ionosphere" itself: ions in this layer are what reflect and refract radio waves, letting broadcasters send signals over hundreds or thousands of kilometres using skywave propagation.

Let's summarize:

• The ionosphere contains charged particles that reflect radio waves back toward Earth.
• Troposphere, exosphere, and thermosphere do not provide this specific ionisation-based reflection.

So the correct layer is the ionosphere, option (B).