If refractive index is n,
n= sin i / sin r
where i = angle of incidence
r = angle of refraction
As joinedup has advised, substitute 90 degrees for r, and the equations wll give you angles of incidence (iin this case of TIR these are the critical agles, i.e. the smallest angle of of incidence that will lead to the ray being reflected rather than transmitted).
n= sin i / sin r
where i = angle of incidence
r = angle of refraction
As joinedup has advised, substitute 90 degrees for r, and the equations wll give you angles of incidence (iin this case of TIR these are the critical agles, i.e. the smallest angle of of incidence that will lead to the ray being reflected rather than transmitted).
(edited 7 years ago)
Whenever you hear critical angles on a question just remember to plug in 90 degrees for the reflected ray part, it just means it's going to stay inside the medium at the boundary. Google "critical angle" in images for a better and comprehensive pic.
Original post by macpatelgh
If refractive index is n,
n= sin i / sin r
where i = angle of incidence
r = angle of refraction
As joinedup has advised, substitute 90 degrees for r, and the equations wll give you angles of incidence (iin this case of TIR these are the critical agles, i.e. the smallest angle of of incidence that will lead to the ray being reflected rather than transmitted).
n= sin i / sin r
where i = angle of incidence
r = angle of refraction
As joinedup has advised, substitute 90 degrees for r, and the equations wll give you angles of incidence (iin this case of TIR these are the critical agles, i.e. the smallest angle of of incidence that will lead to the ray being reflected rather than transmitted).
No sure, do you realize that using your formula for refractive index and apply the suggestion of substituting r with 90 deg, the value of n is less than 1.00. (If this does not shock you, then I am quite worried.
)Spoiler
It means that the material is optically less dense than air.
Medium Refractive index
water 1.33
diamond ~2.4
glass ~1.5 (depending on what types of glass)
Thanks for pointing this error out Eimmanuel; of course you are right!
Because we are taking (for TIR to be at all possible) a ray potentially coming out of glass (or diamond) out into air, and the definition of refractive index states entry from air into a more optically dense material, therefore the 90 degrees must be put into the numerator.
Much obliged for your input and apologies for the oversight.
Because we are taking (for TIR to be at all possible) a ray potentially coming out of glass (or diamond) out into air, and the definition of refractive index states entry from air into a more optically dense material, therefore the 90 degrees must be put into the numerator.
Much obliged for your input and apologies for the oversight.
Original post by Sheeba.07
Hi there! Thank you so much for the help and no there was no data which is why I was slightly confused. However thank you very much for the help!
You can want to look into this site to understand how refractive index and critical angle are related.
http://www.physicsclassroom.com/class/refrn/Lesson-3/The-Critical-Angle
Original post by Eimmanuel
You can want to look into this site to understand how refractive index and critical angle are related.
http://www.physicsclassroom.com/class/refrn/Lesson-3/The-Critical-Angle
http://www.physicsclassroom.com/class/refrn/Lesson-3/The-Critical-Angle
Thank you for your help!
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