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: Optics Problem: What am I doing wrong?

  1. Jan 29, 2005 #1
    Hey Everyone..
    I'm having trouble with this question, I think I have this question figured out but my answer is coming out incorrect... Tell me if there is a flaw in my logic.. question is:

    "Suppose that a luminous star of radius R1=1.74×108 m is surrounded by a uniform atmosphere extending up to a radius R2=4.28×108 m and with index of refraction n=1.82. When the sphere is viewed from a location far away in vacuum, what is its apparent radius?"

    What I did was consider the outer edge of the atmosphere a spherical refracting surface.. and using the equation: n1/P + n2/q = (n2-n1)/R
    (sorry for not using latex)

    And then I took a point from the star's surface, and take the distance form the atmosphere to that point the image distance (where P is just R2 - R1).
    I also took n1 as 1.82 and n2 as 1 since it's just vacuum.. and according to the sign conventions the radius should be negative..

    After I got the image distance (which was negative, a virtual image), I subtracted it's absolute value from R2, and that should be apparent radius. Am I wrong?

  2. jcsd
  3. Jan 29, 2005 #2
    btw, the answer I got when I did this was 2.313x10^8 m

    there's a hint on that question but it made sense to me.. Here it is just in case: "What is special about the case R2 > n*R1? "
  4. Jan 30, 2005 #3
    Ideas anyone?
  5. Jan 30, 2005 #4


    User Avatar
    Science Advisor
    Homework Helper

  6. Feb 1, 2005 #5


    User Avatar
    Homework Helper

    Last edited: Jun 29, 2010
  7. Feb 2, 2005 #6


    User Avatar
    Science Advisor
    Homework Helper

    I found the original problem online and it seems that they wanted the answer in your form, since one had to incorporate the given R2>nR1
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook