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 homework help

  1. Nov 22, 2009 #1
    1. The problem statement, all variables and given/known data
    Hi all its me again.need help again =]
    well basically i am stuck at b part (iii), no idea on how to find out theta 3 =/
    inwsu8.png
    2. Relevant equations
    hmm 180- something =/? no idea


    3. The attempt at a solution
    well i though at first that it would be this way:
    180=90+19.47 =/ but.. on the mark scheme the answer is way low/
    Thanks.
     
  2. jcsd
  3. Nov 22, 2009 #2

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Re: Refraction

    if you got the first two parts right then you must know Snell's law
    the only thing to be carefull about is that theta3 will be measured from the normal, and remember which way the light bends going from high n to low n
     
  4. Nov 22, 2009 #3
    Re: Refraction

    yea i do but doesn't snells law work on ratio of indices between two mediums =/? as in this case theta 2 and 3 both are in the same medium?
     
  5. Nov 22, 2009 #4

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Re: Refraction

    looking at the diagram more closely - have you heard of total internal reflection?
     
  6. Nov 22, 2009 #5
    Re: Refraction

    yeah which occurs when light propagates from dense medium to less dense and i got the critical angle, its just finding out theta 3 bit.
     
  7. Nov 22, 2009 #6

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Re: Refraction

    So having determined that it reflects at A what is the angle - remember that TIR is the same as normal reflection
     
  8. Nov 22, 2009 #7
    Re: Refraction

    err... would it be 90degree or same as theta 2
     
  9. Nov 22, 2009 #8

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Re: Refraction

    imagine the bottom of the prism is a mirror draw the reflected ray from where the theta2 ray hits A
    then angle theta 3 is between this reflected ray and the normal at A
     
  10. Nov 22, 2009 #9
    Re: Refraction

    ooh.. i still don't get it sorry for being such a nuisance lol ,looking at the time its 1.20 am xD and i got college in less than 8 hours ,...wonder what am i missing here hmm..
     
  11. Nov 23, 2009 #10
    Re: Refraction

    OO hi all back again and sorry for the late reply.I think i have figured it out.
    what i did was basically finding all of the unknown angles lol yea.. ugh.. image hosting sites are blocked at my college , cant upload screenshot.this is what i did:
    180-(135+19.47)=25.53.
    => so to get theta3
    90-25.53=64.47 which is >critical angle , hence TIR.
    Thanks alot mgb phys =]
    i will be posting more threads soon xD.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Refraction homework help
  1. Refraction help (Replies: 1)

Loading...