Electromagnetic waves can interact with objects smaller than their wavelength, but the nature of the interaction depends on the size of the object relative to the wavelength of the wave.
When an electromagnetic wave encounters an object, such as a solid particle or a molecule, several interactions can occur. These interactions can be broadly categorized into two regimes: the geometric optics regime and the wave optics regime.
In the geometric optics regime, where the size of the object is much larger than the wavelength of the wave, the wave interacts with the object based on its geometrical features. This regime is governed by the laws of geometric optics, where the wavefronts of the electromagnetic wave are considered as rays that reflect, refract, or diffract when they encounter the object. This regime is applicable to macroscopic objects like mirrors, lenses, and everyday objects that we encounter in our daily lives.
In the wave optics regime, where the size of the object is comparable to or smaller than the wavelength of the wave, the wave interacts with the object on a wave-like scale. At these scales, phenomena such as diffraction and interference become prominent. When an electromagnetic wave encounters an object of comparable size to its wavelength, the wave can diffract around the edges of the object, leading to a bending and spreading of the wave. This diffraction phenomenon is a characteristic of wave behavior and can occur for waves such as light, radio waves, and microwaves.
However, when the size of the object becomes much smaller than the wavelength of the wave, the wave interactions become less significant. This is because the wavefronts tend to "smooth out" the details of the object, and the wave passes over or around the object without significant scattering or diffraction. The interaction becomes less noticeable, and the object's effects on the wave become negligible. This phenomenon is known as the "Rayleigh scattering regime" or "geometric optics approximation." It is commonly observed when waves interact with nanoparticles or molecules that are much smaller than the wavelength.
In summary, electromagnetic waves can interact with objects smaller than their wavelength, but the nature of the interaction depends on the size of the object relative to the wavelength. In the geometric optics regime, the wave interacts based on the object's geometrical features, while in the wave optics regime, diffraction and interference effects become prominent. However, when the object size becomes much smaller than the wavelength, the wave interactions become less significant, and the object's effects on the wave become negligible.