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Critical Angle

Hi, there's just one thing that's confused me about the Wave Properties part of the AQA Physics A syllabus. Working out the critical angle.

I know how to find it, it's just I'm not sure how it's derived from Snell's Law?

Snell's Law is n = sin i/sin r, and since i = C, sin i must = sin C. Also, r = 90, so sin r = 1. Wouldn't this make n = sin C/1 rather than n = 1/sin C?


Thanks in advance :smile:
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welwyn
the critical angle is the angle of incidence IN THE MATERIAL for which the angle of refraction if 90 degrees (OUT OF THE MATERIAL).

when you say, eg from air into glass, the refractive index of the glass is n, then the refractive index from glass to air is 1/n.

so 1/n = sinC/sin90
1/n = sinC

One of the requirements of Total Internal Reflection is that i must be larger than C. This only really applies when the boundary is from a more-dense medium to a less-dense medium.

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