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Bending the light

  1. Jul 24, 2014 #1
    I saw this experiment:

    The light from laser is bending in small hole and moving in spring. I don't understand why.
    Please, can you tell me why? Why does spring moving in spring, not in air? It will happens in each spring? Why it occurs?

    Thank you very much
    Last edited by a moderator: Sep 25, 2014
  2. jcsd
  3. Jul 24, 2014 #2


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    Staff: Mentor

    Like the description on the video says, this is called "total internal reflection."



    A Google search finds many other pages about it.

    The basic explanation for it is the behavior of Snell's Law (which describes the refraction of a light ray at a boundary) when the light travels (or tries to travel) from a material with a higher index of refraction (e.g. water) to a material with a lower index of refraction (e.g. air).
  4. Jul 24, 2014 #3
    The ray reflect back to the watter, not to air because it is total reflection, OK. So, why the ray don't go back to the watter in the bottle but go to the spring?
  5. Jul 24, 2014 #4


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    Staff: Mentor

    Total internal reflection is like ordinary reflection from a mirror. When a light ray hits a mirror at a glancing angle (not "head-on") it doesn't come backwards on itself.

    More precisely, a mirror reverses a light ray only along the direction perpendicular to the mirror surface, not along the direction parallel to the mirror surface.
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