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Diffraction at an object - diagram?

  1. Feb 4, 2013 #1
    I was wondering if anyone would have a link to, or have, a diagram showing light wave diffraction at an obstacle?

    That is, when it collides with an obstacle, then diffracts around the corners.

    It's easy to find diagrams for slot experiments, but am having problems finding a good diagram for this.

    Thanks!
     
  2. jcsd
  3. Feb 4, 2013 #2

    sophiecentaur

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    As it happens, the diffraction pattern from a slot (aperture) and the pattern from an obstacle the same width, are the same but inverse. This is not altogether surprising when you think that the slot is what you get when you take the obstacle away and vice versa. If you let the light from the slot add to the light from the obstacle, you get an unobstructed uniform resulting field.

    So, for a long slot, you get a
    sin(x)/x pattern and , for a single rectangular obstruction of the same size, you get a

    1-sin(x)/x pattern.

    The (optical) diffraction pattern for a slot is, of course, easier to see because your eyes are not blasted by all that unobstructed light that gets past a single obstacle. If you take a receiving antenna round behind a metal obstruction, however, it is often possible to detect a set of maxes and mins right where you'd expect to find a shadow.

    See this link and many more. I searched Google for "diffraction pattern obstacle".
     
  4. Feb 4, 2013 #3
    Thanks sophiecentaur.

    It was really a flat/straight obstacle, rather than a round obstacle I was looking for.

    I should have been more clear on that.

    Something like this:
    http://www.google.co.uk/imgres?q=diffraction+pattern+obstacle&start=372&um=1&hl=en&tbo=d&biw=1920&bih=890&tbm=isch&tbnid=MMB_5UkCCUwOaM:&imgrefurl=http://fizik-fizik.blogspot.com/2010_01_01_archive.html&docid=XJ_aIqefGFA4cM&imgurl=http://4.bp.blogspot.com/_FAgA6-CHYr8/TUQNdArxW7I/AAAAAAAAAuQ/XQYhajZNTZk/s1600/untitled.bmp&w=840&h=304&ei=aegPUZmvAsWd0AW35oGgDQ&zoom=1&ved=1t:3588,r:92,s:300,i:280&iact=rc&dur=687&sig=111767905124275248331&page=10&tbnh=122&tbnw=317&ndsp=46&tx=98&ty=28
    which is the only such diagram of its kind I can find on the internet!
     
  5. Feb 4, 2013 #4

    jtbell

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    Here's a Java applet that displays diffraction patterns for various shapes. You can vary the size, and switch between apertures and obstacles.

    http://www.falstad.com/diffraction/
     
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