1. Not finding help here? Sign up for a free 30min 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!

Index of refraction, calculate frequency. ~ stuck at 2 unknown variables

  1. Mar 3, 2008 #1
    1. The problem statement, all variables and given/known data

    An laser is used of wavelength 544 x 10^-7 m (in air) for eye surgery. The index of refraction of the fluid in an eye is n = 1.43. Calculate the frequency of the laser waves in the eye.

    n = 1.43
    L1=544 x 10^-7
    L2=
    f =


    2. Relevant equations

    n=L1/L2

    L1 being the wavelength in "air"
    L2 being the wavelength in the eye

    f=v/L

    L=v/f

    3. The attempt at a solution

    so, given n and L1 its simple to find L2, so I now know the wavelength in the eye. Yet I can't seem to derive the frequency.

    so:

    n=L1/L2

    1.43= (5.44 x 10^-7) / (v/f)

    the frequency remains constant for both wavelengths.

    so simply I would have to find the velocity of L1 or L2 that would be the frequency "within the eye"

    v1/L1=v2/L2

    the velocity is not the same so I now have 2 unknown variables.

    I KNOW this isn't hard, my minds just shot right now
     
    Last edited: Mar 3, 2008
  2. jcsd
  3. Mar 3, 2008 #2

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    You already said the correct answer. The frequency is the same. The wavelengths and velocities are different, but they both change by the same factor.
     
  4. Mar 3, 2008 #3
    Thanks Dick,

    I had though that, but then that same factor that they change by is simply equal to n. Using n for the frequency wouldn't create the correct answer. I'm just not thinking right.

    If you or anyone else could elaborate it would be greatly appreciated.

    I know this isn't complicated and I'm embarrassed to continue asking when I'm sure this is so simple..
     
    Last edited: Mar 3, 2008
  5. Mar 3, 2008 #4

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    Air has basically n=1. f=v/lambda. In a different medium v->v/n, lambda->lambda/n. The frequency is unchanged. This is also sort of obvious. A thing that measures frequency is counting waves as they pass. If it's located outside of the eye it counts f waves per second. If it's inside the eye it must also count f waves per second. Otherwise, some 'waves' are getting lost somewhere. Where could they go??
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Index of refraction, calculate frequency. ~ stuck at 2 unknown variables
Loading...