The absorption of radio waves by the atmosphere depends on

Options

A. their distance from the transmitter
B. the polarisation of the wave
C. their frequency
D. the polarisation of the atmosphere

Answer

To solve the question regarding the absorption of radio waves by the atmosphere, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding the Interaction of Radio Waves with the Atmosphere**:
- Radio waves are a form of electromagnetic radiation that interacts with different layers of the atmosphere, particularly the ionosphere.

2. **Role of the Ionosphere**:
- The ionosphere is a region of the atmosphere that contains a high concentration of ions and free electrons. This layer plays a crucial role in the behavior of radio waves.

3. **Reflection and Absorption**:
- When radio waves reach the ionosphere, part of the wave is reflected back to space, while a significant portion is absorbed by the ionosphere.

4. **Critical Frequency**:
- The critical frequency is a key concept in understanding how radio waves interact with the ionosphere. It is defined as the frequency above which radio waves can penetrate the ionosphere rather than being reflected.
- The critical frequency (fc) is given by the formula:
\[ f_c = 9 \sqrt{N_e} \]
where \(N_e\) is the electron density in the ionosphere.

5. **Frequency Dependence**:
- If the frequency of the incident radio wave is above the critical frequency, the wave will penetrate the ionosphere and may get absorbed.
- Conversely, if the frequency is at or below the critical frequency, the wave will be reflected back into space.

6. **Conclusion**:
- Therefore, the absorption of radio waves by the atmosphere primarily depends on the frequency of the radio waves. Higher frequencies can penetrate and may be absorbed, while lower frequencies are reflected.

### Final Answer:
The absorption of radio waves by the atmosphere depends on the frequency of the radio waves.

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