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: Refraction angle physics help

  1. May 14, 2006 #1
    For each of the following cases, will the light rays be bent toward or away from the normal?

    a. ni > nr, where the angle of ni = 20
    b. ni < nr, where the angle of ni = 20
    c. from air to glass with an angle of incidence of 30
    d. from glass to air with an angle of incidence of 30

    for a, i put toward. b i think is away (but i'm not sure why it would be) and i am not sure about c and d

    thanks in advance
     
  2. jcsd
  3. May 14, 2006 #2

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Do you know an equation that would help to answer these questions.

    Regards,
    George
     
  4. May 14, 2006 #3

    Hootenanny

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You are correct for a and b. Perhaps if you drew a diagram, it would make the answer more apparent. Where are the angles measured from?

    As for c and d. Consider snell's law, what happens when a light ray travels through the interface from a lower refractive index (air) to a higher (glass) and visa versa.

    ~H
     
  5. May 14, 2006 #4
    well i think this is a conceptual problem, so no equation is needed. but the equation i have to work with is (ni)(sinXi)=(nr)(sinXr)

    --index of refraction of first medium x sine of the angle of incidence = index of refraction of second medium x sine sine of the angle of refraction
     
  6. May 14, 2006 #5
    o ok thanks
     
  7. May 14, 2006 #6

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I find that that looking at a physics problem from different perspectives is often useful. As Hootenanny has indicated, diagrams here are very useful, but I like also to verfiy things with mathematics.

    Note that the graph of sinx is increasing for x between 0 and 90, i.e., if sinx2 > sinx1, then x2 is greater than x1.

    Now consider a) ni > nr. In order for ni sinXi = nr sinXr to hold, this means that sinXi < Sin Xr, which in turn, from what I wrote above, means that Xi < Xr. Now, a diagram shows what happens with respect to bending towards/ away from the normal.

    Regards,
    George
     
  8. May 14, 2006 #7
    o thank you both
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook