Diffraction
When a wave meets an obstacle or a gap it will spread out or diffract. This is why shadows are fuzzy. Waves will only diffract around objects that are about the size of their wavelength: if they are smaller than that, they won't have to diffract very much or larger than that and they may be more of a wall and they will just reflect off it.
When it comes to gaps:
If a gap is smaller than the wavelength of the wave, it can't fit through!
If a gap is about the same size as the wavelength, it will diffract a lot and you will get a semicircular pattern.
If the gap is larger than the wavelength it will diffract less.
If a gap is smaller than the wavelength of the wave, it can't fit through!
If a gap is about the same size as the wavelength, it will diffract a lot and you will get a semicircular pattern.
If the gap is larger than the wavelength it will diffract less.