Physics homework help (again)

[Jess]

Please please help me before tomorrow afternoon!!



A fiber optic line is composed of a core with an index refraction of 1.47 and is coated with a material of index 1.31. What is the minimum angle at which the light must enter from the air to the inner core of the cable so as to result in total internal reflection within the fiber optic cable? (Hint: This is a two part problem. First, consider the critical angle within the cable as the light hits the boundary between the cored and the coating material.)

[Anselmo]

n1=1.47 n2=1.31

sin α lim= n2/n1
sin α lim=0.89
α lim=62º
I don't know if it's this what you want to know...

[Jess]

I don't think that's it, it's a two part problem :/

[Anselmo]

I really can't see how this can be an exercise with 2 parts.... with any angle superior to sin α lim= n2/ni it will happen total internal reflection. I checked my book and they have examples of exercises and in all of them they only make 1 step to get to the result.

Edit: i just came back from school and my teacher solved this exercise the same way as i solved it above. But she suggested that maybe the part1 is get from n1 * sin(theta1) = n2 * sin(theta2) to sin α lim= n2/n1 and the part 2 is solve it and get a result