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!

Refraction of Light question assistance needed

  1. May 19, 2015 #1
    As revision for my upcoming physics exam, I'm doing an old exam paper from a previous year of the course, for which the answers aren't published. However, I'm stuck on a basic angle of refraction question:
    "A light ray makes an angle of 35degrees to the surface of an oil layer. [A diagram is attached, which shows the light ray travelling through air until it hits the oil surface]. The air's n=1.00, and the oil''s n=1.47. What is the angle of refraction of the light ray in the oil?"

    It's a multichoice answer, and the answers are A) 35degrees, B) 56.1degrees, C) 55.9degrees, D) 33.9degrees, and E) 67.7.
    However when I use the n1*sin(theta1) = n2*sin(theta2) method, my answer is always equal to 22.97degrees? Which is equal to none of the multichoice answer values? And because there are no published answers, I can't check the correct answer.
    Have I done something wrong? Or is there a mistake in the exam paper? Thank you for any and all help!
    [P.S. my calculator is definitely set in degrees.]


    Relevant equations:
    n1*sin(theta1) = n2*sin(theta2)


    The attempt at a solution:
    1 * sin(35) = 1.47 * sin(theta2), therefore sin-1 (sin(35)/1.47) = theta2 = 22.97degrees.
     
  2. jcsd
  3. May 19, 2015 #2

    andrevdh

    User Avatar
    Homework Helper

    Try 90o - 35o as the incident angle.
    The incident angle for Snell's law is measured with respect to the normal to the surface.
     
  4. May 21, 2015 #3
    Thank you very much! A dumb mistake on my part; you've saved me from embarrassing myself in front of my lecturer when I went to ask him for help, and the extra info at the bottom was also very helpful, thank you again!
     
  5. May 21, 2015 #4

    andrevdh

    User Avatar
    Homework Helper

    Don't be afraid to make mistakes or ask questions (and hopefully do not break anything in the process). That is (mostly) how we learn.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Refraction of Light question assistance needed
Loading...