As the e.m. waves travel in free space

Options

A. absorption takes place
B. attenuation takes place
C. refraction takes place
D. reflection takes place

Answer

To solve the question regarding the behavior of electromagnetic (e.m.) waves as they travel in free space, we need to analyze the options provided and understand the principles of wave propagation.

### Step-by-Step Solution:

1. **Understanding Electromagnetic Waves**: Electromagnetic waves are waves of electric and magnetic fields that propagate through space. They can travel in a vacuum (free space) without the need for a medium.

2. **Wave Propagation in Free Space**: When an e.m. wave is emitted from a transmitter, it spreads out in all directions. The wavefronts take the shape of expanding spheres as they move away from the source.

3. **Energy Conservation**: As the e.m. waves travel, the energy they carry is conserved. However, as the wavefronts expand, the energy is distributed over a larger area. This means that the energy density (energy per unit area) decreases as the distance from the source increases.

4. **Amplitude and Energy Relationship**: The energy of a wave is proportional to the square of its amplitude. Therefore, as the energy density decreases due to the expansion of the wavefronts, the amplitude of the wave must also decrease to conserve energy.

5. **Identifying the Correct Process**: The decrease in amplitude and energy density as the wave travels indicates that the wave is experiencing attenuation. Attenuation refers to the reduction in the strength (amplitude) of the wave as it propagates through space.

6. **Evaluating Other Options**:
- **Absorption**: This refers to the conversion of wave energy into other forms (like heat) by the medium, which is not applicable in free space.
- **Refraction**: This is the bending of waves when they pass from one medium to another, which does not occur in free space.
- **Reflection**: This is the bouncing back of waves when they encounter a barrier, which is also not relevant to free space travel.

7. **Conclusion**: Since the only process that describes the behavior of e.m. waves traveling in free space, where their amplitude and energy decrease, is attenuation, the correct answer is that attenuation takes place.

### Final Answer:
**The correct option is B: Attenuation takes place.**

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