The inverse square law describes how the intensity of a wave diminishes with increasing distance from the source. It states that the intensity of a wave is inversely proportional to the square of the distance from the source. Mathematically, it can be expressed as:
I ∝ 1/distance²
where I represents the intensity of the wave.
The inverse square law applies to the spreading of waves in a homogeneous medium, assuming no absorption or scattering. However, when waves travel through different media, such as air or vacuum, there can be variations in their behavior.
In the case of radio waves, when they propagate through a vacuum, they will follow the inverse square law. In a vacuum, there are no particles to interact with the waves, so they travel in straight lines, spreading out according to the inverse square law as they move away from the source.
On the other hand, when radio waves propagate through air, they can experience absorption, scattering, and other interactions with the molecules in the medium. These interactions can cause the waves to deviate from the ideal inverse square law behavior. As a result, the waves may become less collimated (more dispersed) in air compared to a vacuum.
So, if you were to emit radio waves into a vacuum chamber, the waves would generally be more collimated than in air, assuming all other factors are constant. In a vacuum, the waves would spread out according to the inverse square law, whereas in air, they may disperse more due to interactions with the air molecules.