# Refraction on the edge of mediums

Say I have this setup :

Here a light ray (in red) is incident on the point A in such a way that it is collinear with AB, and the indices of refraction are as mentioned in the figure. So my question is where will the light ray go?

Here is what I thought

• If the ray goes towards the medium with refractive index n3, then as n3 < n2, it will tend to go towards n1.
• But if the ray goes towards n1, then as n1>n2, it will tend to go towards n3.

Therefore, I think that the ray will trace the line segment AB. But then what will happen at the point B??

P.S. Here, ni means the medium with the refractive index as (mu)i

• I meant that I am not sure what would happen, and that I expected tracing the line segment to be the outcome. – Eagle Feb 16 at 19:15
• It might be best to consider the case where you aren't along boundaries and then take limits. The problem is at point A you don't have a way to define what medium the light is propagating through. – Aaron Stevens Feb 16 at 19:20
• But what if I have an experimental setup, where I can vary the angle of incidence at point A in such a way that the refracted ray varies from going to n3 to n1. So what will happen at that transition? – Eagle Feb 16 at 19:24
• I didn't think about it. That might be a possibility too, but won't it depend on the relative refractive indices, so that we might have two cases - one where total internal reflection take place, and the other where it doesn't. – Eagle Feb 16 at 19:30
• At least one kind of electromagnetic wave can propagate along the interface between two media: a surface plasmon polariton. See [rua.ua.es/dspace/bitstream/10045/75492/1/…. – S. McGrew Feb 16 at 21:18