5.3 Diffraction
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In addition to reflection and refraction, waves can be made to change direction due to diffraction. Diffraction is when waves are bent around objects. When a wave moves past an object or through a tight gap, the edges of waves spread out (diffract). The extent of diffraction depends on the wavelength of the waves and the width of the gap. There are three broad scenarios:
- The gap is much wider than the waves’ wavelength. When this is the case there is little diffraction, meaning that the waves continue pretty much in the same direction.
- Gap is slightly wider than the waves’ wavelength. Here only the waves at the edges diffract and change their direction.
- The gap is very narrow compared to the waves’ wavelength. When this is the case, the waves diffract greatly and go off in all kinds of directions.
However, we need to remember that the same gap will have different effects on waves that have different wave lengths. An easy way to think of diffraction is to think of a harbour with waves travelling through the gap where boats come in (the harbour entrance).