Date: Sat, 22 Jun 2002 12:38:37 -0700 (PDT)

Author: William Beaty

Subject: Re: razor blade diffraction


On Sat, 22 Jun 2002, BeverleyBowyer wrote:

> I do have a laser, but even using that I don't see anything very
> interesting. I was hoping to get the criss-cross pattern in the holes
> that you see in all the text books. How crucial is it to have a really
> clean blade? Do you need a really dark room? What sort of distance
> should there be between the components? If using white light, should
> you send it through a pinhole first? Should I use a lens?

Which criss-cross pattern? The edge of a razor blade demonstrates
interference, but there is no criss-cross pattern. Can you give a
textbook page which has the photo?

The diffraction pattern for a single razor blade should look like a big
black shadow (the blade), and on the straight edge of the shadow you
should see some straight dark lines parallel to the edge of the shadow.
Those lines are the "interference fringes," and are the whole point to
performing the demo.

If you use TWO blades, and bring their edges together, then the group of
interference fringes on each blade-shadow will combine to form the classic
"single-slit diffraction" pattern (a central bright line with dimmer
parallel lines on either side.)

Holes? Do you mean the holes in the razor blade?

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