Finding angle of refraction given angle of incidence?

[Martin Hanna]

Can someone help me in solving this question ?

my attemp is sin42/sin 90 to get the refractive index then n =sin i/sin r to get c
and for b n=1/sinc

 

[TSny]

Welcome to PF!

Try to answer part (i) first by examining the diagram and using a little geometry.

 

[Martin Hanna]

Thanks for responding but i am trying but can't figure it out its probably right there in my face but i just can't see it yet

 

[TSny]

What is the value of the angle DBM shown below?

 

[Martin Hanna]

that would be 90 ?

 

[TSny]

Yes, I think that's what you are supposed to assume. The fisherman's net (at D) is assumed to be essentially at the surface of the water.

 

[Martin Hanna]

so there fore the angle of incidence is 90 so that means C would be a critical angle

 

[TSny]

so there fore the angle of incidence is 90 so that means C would be a critical angle

Yes. From the diagram, can you determine the value of the critical angle in degrees?

 

[Martin Hanna]

42 ? i doubt you can just determine it from looking at the diagram as the question asks to calculate it

 

[TSny]

Note that the line connecting point A to Nemo's eye is a straight line.

 

[Martin Hanna]

therefore c must be 180-(42+90)

 

[TSny]

Yes

 

[Martin Hanna]

well it makes sense because the answer is 48 and 48 is the critical angle of air-water boundary so now i find the refractive index 1/48

 

[TSny]

Why 1/48?

 

[Martin Hanna]

because there is a formula which says that N(Refractive index) = 1/ sin C(48) oh i see yeah I am suppose to sin the 48

 

[TSny]

Yes, good.

 

[Martin Hanna]

thank you very much