Final answer:
Large waves encountering a small hole in a barrier undergo diffraction, spreading out in a pattern that provides protection at certain angles within a harbour.
Step-by-step explanation:
When a large wave approaches a barrier with a small hole, the wave is likely to undergo diffraction after it encounters the barrier. This is because when the size of the opening is comparable to the wavelength of the incident wave, diffraction effects become significant. For the scenario where ocean waves with a 20.0-m wavelength approach a 50.0-m-wide opening, the wave will spread out after passing through the opening and the diffraction pattern will protect certain areas within the harbour at specific angles from direct wave action. To determine the protection angle, one would need to use principles derived from the study of wave behavior, including the wave's wavelength and the width of the opening in the barrier.