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So, when I point a laser at a piece of wire (pointed at a specific angle), a circle of light appears on a wall behind it (see image below). I am trying to see why this happens and if there are any readings on this. Could anyone give some tips on what I should search for or any references?

enter image description here
(screenshot from this youtube video)

So this is a problem for a physics tournament, but I haven't tried it myself yet. However I have found a video depicting what I mean.

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    $\begingroup$ A reference for what, exactly? It's not all clear to me what it is you are doing that you want to search. $\endgroup$ – Kyle Kanos Jan 28 '15 at 1:27
  • $\begingroup$ Sorry for being so unclear, I'm new to this and was in a rush typing up the question. Will edit shortly. Thanks! $\endgroup$ – Tao Tien Jan 28 '15 at 13:49
  • $\begingroup$ This is a problem for a physics tournament, and the problem is basically written exactly as I asked, so I'm completely lost too. $\endgroup$ – Tao Tien Jan 28 '15 at 14:08
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    $\begingroup$ I see what you mean now, the video really helped. I've added a screenshot from the video so that others can see what you mean without clicking away (as well as add some grammar fixes). $\endgroup$ – Kyle Kanos Jan 28 '15 at 14:20
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    $\begingroup$ I suspect that it's going to be related to diffraction about the sharp point of the pin. $\endgroup$ – Gremlin Jan 29 '15 at 11:03
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So I did it myself and figured it out. It's just really simple reflection.

enter image description here

Basically the wire acts as a mirror, albeit a curved one. Because the light from a laser is straight, we won't have messy light. When a laser reflects off of a flat surface, it keeps going straight. However when it reflects off a small curved surface (i.e a wire), the laser rays all go different ways, and create a circle of light.

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  • $\begingroup$ From the screenshot, the circle looks closed and uniform in intensity, which is odd if reflection is the sole cause. $\endgroup$ – user27118 May 21 '15 at 17:46
  • $\begingroup$ But how about the dark fringes? $\endgroup$ – David 2000 Jul 1 '15 at 23:46

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