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Question

# In the diagram shown, a light ray is incident on the lower medium boundary at an angle 45∘ with the normal. Light ray become tangential to the top part of medium−2 after all kind of refraction for μ2>√2. Which of the following statements is/are true?

A
If μ2>2 then angle of deviation is 45.
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B
If μ2<2 then angle of deviation is 90.
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C
If μ2<2 then angle of deviation is 135.
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D
If μ2>2 then angle of deviation is 0.
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Solution

## The correct option is B If μ2<√2 then angle of deviation is 90∘. Critical angle is given by θc=sin−1(μ2μ1)=sin−1(μ22) If μ2<√2, then total internal reflection takes place and that ray reflects back, the angle of deviation is 180∘−(45∘+45∘)=90∘ If μ=√2, then the ray passes tangentially at the first medium, the angle of deviation is 180∘−(45∘+90∘)=45∘ If μ>√2, then the ray enters the second medium and, grazes the interface of medium−2 & 3 as shown in figure. So, the angle of refraction is 90∘ in medium 3. The deviation is 180∘−(45∘+90∘)=45∘.

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