Electromagnetic (EM) waves, such as visible light or radio waves, travel through air as a result of the oscillations of electric and magnetic fields. These waves are composed of synchronized oscillations of electric and magnetic fields, which are perpendicular to each other and propagate perpendicular to the direction of wave travel.
When an EM wave travels through air, it interacts with the molecules present, even though the size of the molecules is significantly larger than the wavelength of the EM wave. The interaction between EM waves and molecules is primarily based on the electromagnetic force.
As an EM wave passes through a medium like air, the electric field component of the wave exerts forces on charged particles within the molecules, causing them to undergo slight displacements or vibrations. These charged particles can include electrons or even the atomic or molecular nuclei. However, it's important to note that these displacements are typically very small.
The magnitude of the interaction between EM waves and molecules depends on several factors, including the frequency of the wave and the nature of the molecules involved. If the frequency of the EM wave matches the natural resonant frequency of a molecule or a group of molecules, a phenomenon known as resonance can occur. Resonance can lead to stronger interactions between the EM wave and the molecules, resulting in energy absorption or scattering.
In general, though, the interaction of EM waves with individual molecules in air is relatively weak because the wavelength of EM waves is much larger than the size of the molecules. Therefore, the wave passes through air with minimal absorption or scattering. This characteristic allows EM waves to propagate over long distances through air without significant attenuation.
It's worth noting that in certain situations, such as at higher frequencies or with specific types of molecules, there can be more pronounced interactions between EM waves and matter. For example, at higher frequencies in the microwave or infrared range, rotational or vibrational transitions of molecules can occur, leading to energy absorption. Additionally, in denser media or with more complex materials, scattering and other interactions can become more significant.