Final answer:
Wave diffraction is determined by the size of the opening or obstacle relative to the wavelength of the wave, with the greatest diffraction occurring when the opening is about the same size as the wavelength.
Step-by-step explanation:
The amount by which a wave diffracts, or spreads out, when encountering an opening or an obstacle is determined by several factors. Primarily, the level of diffraction depends on the size of the opening or obstacle relative to the wavelength of the wave.
When the size of the opening is about the same as the wave's wavelength, the wave diffraction is most noticeable. This phenomenon is explained by Huygens's principle, which states that each point on a wave front is the source of a secondary wavelet.
These wavelets spread out in all directions, and the new wave front is the tangent to these wavelets. Consequently, when the opening is smaller, the wavelets that emerge from the edges can spread out more, leading to greater diffraction. Conversely, if the opening is much larger than the wavelength, the wave will not diffract as much and will mostly continue in a straight path.