For large apertures the wave passes by or through the. For very small aperture sizes, the vast majority of the wave is blocked. It occurs when the size of the aperture or obstacle is of the same order of magnitude as the wavelength of the incident wave. However the shorter the waves the less they diffract. When he is further from the gully, he can neither hear nor see the stream. Some of the energy of the sound waves diffracts around the top of the wall. When he is closer to the gully, he can both hear and see the stream. Smaller holes cause waves to diffract more. Because waves are caused by restoring forces that smooth out differences - if you pull a bit of taut string up, it snaps back down to be closer to the adjacent bits of the string. ![]() In the diagram, the mountaineer can hear the stream although he cannot see it. The spreading out of waves when they pass an obstacle is called diffraction. ![]() \) is the actual path difference a wave reflected off the upper surface must travel an extra distance equal to twice the Step Thickness to catch up with a wave reflected off the lower surface. Diffraction is the spreading out of waves as they pass through an aperture or around objects. sound waves that are too quiet for humans to hear.
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