Results 1 to 3 of 3

Math Help - Angles of light hiting a more dense medium

  1. #1
    Junior Member
    Joined
    May 2011
    Posts
    34

    Angles of light hiting a more dense medium

    Sorry I couldn't think of a better title...
    Can any smart person here explain to me why the mark scheme gives very weird answers? my exam is tomorrow and I need help in the questions attached. I had also managed to put the ansewrs in the scan, please anyone explain how to get the answers for b (i) and (ii)

    thanks in advance
    Attached Files Attached Files
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Member
    Joined
    May 2011
    From
    Sacramento, CA
    Posts
    165
    For (1) you need to understand what the angle of incidence is. That vertical line at E establishes the angle of incidence. In particular, that 60 degrees for the ray FE is its angle of incidence. If you have a ray coming in nearly horizontal (or think of pushing FE down to AE), then the angle of incidence must be nearly 90 degrees, as indicated in the answer. As for the rest, it should be established by Snell's law.

    My guess is that (2) is conceptual. I assume that since the ray coming in is nearly horizontal that the refracted ray (i.e., the ray turning inside the medium) at 43 degrees is nearly the critical angle for total internal reflection. Just think about how the critical angle is defined. It is the point at which light would come out horizontal, no? And any adjustment would either allow some light to pass through the surface or be total reflected internally.

    From that we should be able to use Snell's law to answer (iii). Is the medium outside the cube supposed to be air? The speed question is also straight-forward if you think about what defines the indices.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    May 2011
    Posts
    34
    THNAKS!
    I know the critical angle, but I never thought about it the other way round....
    thanks again, I really appreciate your help
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: August 28th 2011, 03:33 AM
  2. Ratio 3 problem medium
    Posted in the Geometry Forum
    Replies: 12
    Last Post: January 21st 2011, 09:15 PM
  3. Roof Light Angles
    Posted in the Trigonometry Forum
    Replies: 0
    Last Post: July 8th 2010, 03:56 PM
  4. Replies: 5
    Last Post: June 20th 2010, 10:12 PM
  5. Motion in a resisting medium
    Posted in the Differential Equations Forum
    Replies: 5
    Last Post: August 30th 2009, 09:37 PM

Search Tags


/mathhelpforum @mathhelpforum