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Asked in CBSE AIPMT 2004 · Snell's law, slabs and apparent depth
Given: red and green enter a rectangular slab obliquely at the same point on the first face.
Idea: the two colours have different refractive indices, so Snell's law bends them through different angles inside the slab.
Green, with the larger μ, is bent more than red, so the two travel along separate lines and reach the far face at two separate points.
The two faces are parallel, so at the second face each ray is bent back by exactly the amount it was bent at the first.
Each emergent ray is therefore parallel to the original beam, just displaced sideways, and the two displacements differ.
So the rays come out from two points, travelling in parallel directions.
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