Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 06/10/2012 10:30:01

Title: Why does the shadow created by a colander have tiny dots in the middle of the holes of light?
Post by: thedoc on 06/10/2012 10:30:01

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?

Title: Re: Why does the shadow created by a colander have tiny dots in the middle of the holes of light?
Post by: RD on 06/10/2012 10:47:43

Similar diffraction mechanism to Arago bright spot ...

Quote

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fen%2Fthumb%2F6%2F6c%2FPoissonspot_simulation_d1mm.jpg%2F200px-Poissonspot_simulation_d1mm.jpg&hash=5e3517c8c73bfc8a0178aee61df34547)

 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 it’s diffraction at a circular aperture rather than by circular obstacle ...

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similar to  a zone plate ... https://en.wikipedia.org/wiki/Zone_plate which has circular apertures.