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A light ray falls on a rectangular glass slab as shown. The index of refraction of the glass, if total internal reflection is to occur at the vertical face, is

1. √3/2
2. (√3 + 1)/2
3. (√2 + 1)/2
4. √5/2

Correct answer: (√3 + 1)/2

Solution

For total internal reflection to occur, the angle of incidence must exceed the critical angle. Using Snell's law and the geometry of the problem, the refractive index of the glass is calculated as (√3 + 1)/2.

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