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# Total internal refraction

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1. Why does the relative refractive index for speeds between 2 materials need to be lower than 1 for TIR to occur, and how would it be like for refractive indices instead of speed?
2. (Original post by Jennifer50)
Why does the relative refractive index for speeds between 2 materials need to be lower than 1 for TIR to occur, and how would it be like for refractive indices instead of speed?
TIR is total internal reflection, not refraction. It happens when the angle of incidence is greater than the critical angle, from a more optically dense material to a less optically dense one.
3. (Original post by TheBride)
TIR is total internal reflection, not refraction. It happens when the angle of incidence is greater than the critical angle, from a more optically dense material to a less optically dense one.
Exactly what he said, and regarding the speed, the wave speeds up as it is refrated from a more dense to less dense medium hence the angle of refraction is greater than the angle of incidence
4. (Original post by voltz)
Exactly what he said, and regarding the speed, the wave speeds up as it is refrated from a more dense to less dense medium hence the angle of refraction is greater than the angle of incidence
It was a question on the aqa as physics paper 2 specimen paper
5. (Original post by Jennifer50)
Why does the relative refractive index for speeds between 2 materials need to be lower than 1 for TIR to occur, and how would it be like for refractive indices instead of speed?

if we set the beam to be the minimum angle of incidence that produces TIR then

this means that

since

6. (Original post by Jennifer50)
Why does the relative refractive index for speeds between 2 materials need to be lower than 1 for TIR to occur, and how would it be like for refractive indices instead of speed?
Also the speed of light in a material is related to the refractive index by

where c is the speed of light in vacuo and v is the speed of light in the medium.

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