Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Snell's law/Deriviation

  1. Jan 19, 2012 #1
    i simply can't figure out how to make the equations work, so i copied everything into pictures.

    Attached Files:

    • brydning.png
      File size:
      10.5 KB
    • 2.jpg
      File size:
      29.3 KB
    • 1.jpg
      File size:
      21.3 KB
    Last edited: Jan 19, 2012
  2. jcsd
  3. Jan 19, 2012 #2


    User Avatar
    Homework Helper

    dt/dx=0 will give local stationary points (minima or maxima). In the general case, there may be several points which satisfy dt/dx=0. So to actually prove that a point is the lowest possible t value, you would need to draw a graph and/or use good reasoning.

    I don't understand why you were taking the limit of dt/dx as x goes to zero. This would give the case where the light goes the shortest distance through the first medium. And taking the limit as x goes to infinity makes no physical sense, because we would expect x<m.

    In this problem, most teachers expect that you just try to solve dt/dx, rather than go in to detail about why this minimises t. I don't know what your teacher is looking for, but I would guess he just wants you to solve dt/dx and provide a reasonable explanation to why it minimises t.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook