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Questions about light

  1. Sep 14, 2011 #1
    1.it's easy to see your reflected image on the glass window of your room during night,while it's hard too see your image during day

    2.when a blue light is placed in the centre of a glass cube,light comes out from the cube as circular spot, while when red light is placed in the cube,light comes out as a rectangular spot

    could you explain the reasons??
  2. jcsd
  3. Sep 14, 2011 #2
    For 1): What reaches your eye is the light coming from the outside showing the trees and the light reflected from the inside showing you. At night, the light from the trees outside is absent, leaving only your mirror image which is then more clearly visible.

    I'm not convinced that 2) is a general effect.
  4. Sep 14, 2011 #3


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    But why is the reflection a left-to-right swapped image and not an up-and-down swapped image!! ;)
  5. Sep 14, 2011 #4


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    It's not, that's just a fault of human designation of what "right" and "left" should be. Put an object up that has four unique points (up, down, left, right). Each point will be directly across from itself in the reflection. There is no swapping.

    So your left hand is still across from your left hand in the mirror. The outer edge of your hand conforms to the outer edge of your hand's reflection, just like the outer edge of your head conforms to the outer edge of your head's reflection.
  6. Sep 14, 2011 #5
    I'm not much into the guru cult that some people on the Internet seem to establish around physicists that are widely know, but incidentally I recently saw an amusing YouTube video of Richard Feynman talking about this:
    Last edited by a moderator: Sep 25, 2014
  7. Sep 16, 2011 #6
    Great answer,Thanks
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