When light is incident on a glass slab, the incident ray, refracted ray and the emergent ray are in three media A, B and C.

Monjur Alahi

When light is incident on a glass slab, the incident ray, refracted ray and the emergent ray are in three media A, B and C. If n1, n2 and n3 are the refractive indices of A, B and C respectively and the emergent ray is parallel to the incident ray, which of the following is true ?

(a) n1 < n2 < n3

(b) n1 > n2 > n3

(c) n1 < n2 = n3

(d) n1 = n3 < n2


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Salim Ahmed Kawsar

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Correct answer is (d) n1 = n3 < n2 

Medium A and C in air, therefore, n1 = n3, but glass slab is of higher refractive index.

∴ n1 = n3 < n2

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