I was wondering if diffraction of a wave can occur when the gap through which the wave passes is shorter than the wavelength itself. Then I came across this website http://www.talktalk.co.uk/reference/encyclopaedia/hutchinson/m0015966.html Which says that "In order for this effect to be observed, the size of the object or gap must be comparable to or smaller than the wavelength of the waves." I would like to know how can diffraction occur when the wavelength is longer than the gap? Wouldn't it be blocked? I don't really understand the mechanism here because every illustration I met just showed some straight and curve lines "as a whole" without drawing out what happens to each single wavelength.