Please Help Me On As-level Physics PHYA2. Got Exam Tomorrow! :)? I have a question from the past paper. I can not find the paper from the so I will have to explain.

BTW, the paper is june 2009 and the question is Q6aii)

Q) An optical fiber used for communications has a core of refractive index 1.55 which is surrounded by cladding of refractive index 1.45.

6a) critical angle is 63.9 deg and incident angle is 60 deg.

Note: Incidence substance is the core.

Q6aii) state why the light ray enters the cladding at Q.

Note: Q is the cladding boundary.

Answer: I know that the incident angle is smaller than the critical angle. (so refraction should occur). However, the incident substance (the core) has a larger refractive index than the cladding, (so TIR should occur).

I just want to know why does refraction occurs if the incident substance (core) has larger refractive index but the incident angle is smaller than the critical angle.

For TIR(total internal reflection) to occur,

1) incident angle should exceed the critical angle. (which it does not)
2) Incident substance (core) has larger refractive index than the cladding. (which is does).

So, why still refraction occurs and not reflection?

For total internal reflection, why does both criteria (1 and 2) have to be met?

Thanks.