1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
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