Will water waves diffract through a gap smaller than their wavelength?

Question

I was wondering what happens when a water wave passes through a gap smaller than its wavelength, does diffraction occur?

Answer 1

... when a water wave passes through a gap smaller than its wavelength, does diffraction occur?

Yes, it will. A water wave is the progressive disturbance of the water molecules due to the viscosity of the liquid (or elasticity for solids). The molecules moving up and down and in principle are not moving forwards. As long as the molecules are smaller the slit, the wave will pass the slit.

In reality there are some phenomena which make it necessary to have a slit much greater the dimension of the liquids molecules:

• The tension as well as the friction between the liquid and the slits walls are limiting the smallest distance of the slit.
• For tiny slits the dispersion of the waves energy behind the slit fades the wave out so fast that the wave would be unobservable.