Vertical double slit experiment separation of bright spots in air and water

  1. 1. The problem statement, all variables and given/known data

    A scientist decides to do the double-slit experiment in a ver-
    tical tube, with the slits at the top and a viewing screen at the
    bottom as shown. With red light from a HeNe laser (632 nm) a
    nice pattern forms on the viewing screen, with the bright spots
    1.50 cm apart.

    Now the scientist fills the tube up with water. What
    is the separation of the bright spots now?

    2. Relevant equations

    I think

    3. The attempt at a solution

    So we know n1 (air) is 1, and n2 (water) is 1.33. I thought the 1.50 cm was x1, so we need to find x2. I figured the L,w, and d would all be the same for both cases so I rearranged the equation so that (Lw)/d=x/n. then I set x1/n1=x2/n2 and solved for x2 and got about 2 cm. This was not right. Any help would be greatly appreciated thank you!
  2. jcsd
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