Optics 2 Question 11

11. A ray of light passes through four transparent media with refractive indices μ1,μ2,μ3 and μ4 as shown in the figure. The surfaces of all media are parallel. If the emergent ray CD is parallel to the incident ray AB, we must have

(2001, 2M)

(a) μ1=μ2

(b) μ2=μ3

(c) μ3=μ4

(d) μ4=μ1

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Answer:

Correct Answer: 11. (d)

Solution:

  1. Applying Snell’s law at B and C, μsini= constant or

μ1siniB=μ4siniC

But AB||CD

iB=iC

or

μ1=μ4

NOTE

The Snell’s law, which the

students read in their plus two syllabus μ=sinisinr is derived from μsini= constant or μ1sini1=μ2sini2

Here : μ1=1,μ2=μ, or sini=μsinr or μ=sinisinr



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