Diffraction of water waves (opening)

 

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A wave spreads out (noticeable diffraction) when the size of the slit is comparable to or smaller than the wavelength.
 

When waves reach a narrow slit, the water in the slit vibrates like a point source. The waves thus sent out from secondary sources along the slit are nearly in-phase when arriving any point in the forward direction. The diffracted wave resembles a circular wave with centre at the slit.

 

 

A wave goes straight when the size of the slit is much larger than the wavelebgth.
 

 

Related applets

1. Diffraction by an obstacle.

2. Bending of waves around a corner.