Homework Help: Why wavelength matters in diffraction

1. Aug 9, 2007

MIA6

Waves pass through a 10.-centimeter opening in a barrierr without being diffracted. This observation provides evidence that the wavelength of the waves is much shorter than 10. cm. This is a multiple-choice question, and this is not the question that I am asking. I want to use this as an example to ask that why wavelength matters in diffraction, like in slit problem. If the wavelength is long, then what happens? If it is short, then?
thanks.

2. Aug 9, 2007

mgb_phys

Diffraction is only significant if the wavelength is similair to the size of the opening. So light diffracts through a pinhole or small slit, electrons diffract in a crystal, water waves diffract in a harbour.

But you don't significantly diffract when walking through a doorway!

3. Aug 9, 2007

But why?

4. Aug 9, 2007

lightgrav

While the same amount of light is effected by the edges,
whether it is a 100 nm opening or a 100 mm opening,
the amount of light that is NOT effected is much greater
for the wider opening.
Rule-of-thumb says that "about 1 wavelength wide"
is *markedly* effected by a single sharp edge ...
so the fraction 2*600 [nm]/100,000,000 [nm] IS effected.
It takes _serious, careful_ work to notice 10 parts per million
(but it can be done ... just wait till next year!)