Why does the shadow created by a colander have tiny dots in the middle of the holes of light?

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Offline thedoc

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Karen  asked the Naked Scientists:
   
Hi Chris,

...Why does the shadow created by the light shining through the holes in a colander have tiny dots in the middle of the "holes of light"?

Hope this makes sense.

Many thanks and best wishes,

Karen Cannard

What do you think?
« Last Edit: 06/10/2012 10:30:01 by _system »

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Offline RD

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Similar diffraction mechanism to Arago bright spot ...

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 an Arago spot, Fresnel bright spot, or Poisson spot is a bright point that appears at the centre of a circular object's shadow due to Fresnel diffraction.
https://en.wikipedia.org/wiki/Arago_spot

but in the colander case itís diffraction at a circular aperture rather than by circular obstacle ...

[attachment=17055]

similar to  a zone plate ... https://en.wikipedia.org/wiki/Zone_plate which has circular apertures.
« Last Edit: 06/10/2012 13:20:46 by RD »