Single slit diffraction problem

[Saado]

I've read that if you want light to diffract through a single slit, the slit opening must be equal too or less than the wavelength of the light. So for example, light of wavelength 600nm would diffract through a slit with width 600nm or less. Is this true? Or am I missing something. Since when I saw a demonstration, the slit width was only 10^-4m apart and the light began to diffract.

 

[ShayanJ]

Its not that the width of the slit should be less than or equal to the wavelength of the light,it only should be comparable to it.
Think about it this way: Imagine you want to throw a basketball through a hole.If the hole is a circle of radius 10m,you will have no trouble doing it and its very improbable that you hit the ball to the edges. But if the hole has a radius of 0.25m,then its really probable that you hit the edges.There is no sharp distinction in the radius spectrum that says radii greater than this one mean that the ball always goes through the hole and radii smaller than this one mean that the ball always hits the edges.
Some people may say that the dimensions of the hole must be somehow that the light "sees" the edges and so acts properly and if the dimensions are somehow that the light doesn't "see" the edges,there will be no diffraction(with a good approximation).

 

[jtbell]

With apertures that are much larger than the wavelength, you do get diffraction effects at the edges, provided of course that the light actually passes by the edges. The width of the aperture can even extend to infinity in one direction, as in knife-edge (straight-edge) diffraction:

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/difopa.html#c1

Here's a picture:

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/bardif.html

A couple more pictures, with non-straight edges:

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/bardif3.html#c1

 

[Saado]

Ahh thank you for the replies