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Shadow on the wall

  1. Mar 9, 2013 #1

    As we know, if one turn a light blub(and no other light is present) on and put his hand in front of a wall to make a shadow, the shadow is blurry, depending on the distance between the hand and the wall.

    I want to ask you if this blur is caused by quantum uncertenty (like this experiment), or it is just a consequence of the wave nature of light ?
  2. jcsd
  3. Mar 9, 2013 #2
    Any observable blurriness is caused by the fact that light sources aren't point sources. So if you draw it out, there will be a region where the light is partially obscured by ur hand, causing the blurriness
  4. Mar 9, 2013 #3


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    hello xzardaz! :smile:
    neither … it's caused by the fact that the bulb isn't a point source

    so the shadow has an "umbra" and a "penumbra", to use solar eclipse terminology

    the "penumbra" is the blurry bit :wink:

    (if you place a screen in between, with a pinhole in it, so as to produce an effectively point source, then the umbra would disappear, but there would be fringes round the edge of the shadow)
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