Get Refraction Homework Help - Stuck on Theta 3? Let Us Help You!

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ibysaiyan
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Homework Statement


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

Homework Equations


hmm 180- something =/? no idea


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.
 

Discussion

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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
 


mgb_phys said:
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

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?
 


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.
 


err... would it be 90degree or same as theta 2
 


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..
 


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 , can't 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 a lot mgb phys =]
i will be posting more threads soon xD.