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Asked in GSEB Board July 2022 · Total internal reflection and optical fibres
Idea: the critical angle is defined as the angle of incidence in the denser medium at which the refracted ray just grazes the boundary.
Snell's law at the boundary: n₁ sin i=n₂ sin r, with n₁>n₂, so r is always larger than i.
As i grows, r reaches its largest possible value 90° first, and the angle of incidence at which that happens is the critical angle: sin C=(n₂)/(n₁).
So when i=C, the angle of refraction is exactly r=90°.
Beyond that there is no refracted ray at all and the light is totally internally reflected.
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