The phenomenon of diffraction occurs when waves encounter an obstacle or a slit, causing them to bend and spread out. The extent of diffraction depends on the relationship between the wavelength of the wave and the size of the slit.
When the wavelength is comparable to the size of the slit or aperture, the diffraction effects are more pronounced, resulting in significant bending and spreading of the wave. This situation is commonly referred to as "single-slit diffraction."
On the other hand, when the wavelength is much larger than the size of the slit, the diffraction effects become less noticeable. In this case, the wave tends to propagate in a straighter path and exhibits less bending and spreading. This scenario is often referred to as the "ray approximation" or "geometric optics limit."
In summary, maximum diffraction occurs when the wavelength is similar to the size of the slit or aperture. As the wavelength becomes larger relative to the slit size, the diffraction effects diminish.