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Question

A light ray from the air is incident (as shown in the figure) at one end of a glass fiber (refractive index μ = 1.5) making an incidence angle of 60 on the lateral surface so that it undergoes a total internal reflection. How much time would it take to traverse the straight fiber of length 1 km

Time taken by light to traverse some distance in a medium t=μxc


A
3.33 μ sec
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B
6.67 μ sec
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C
5.77 μ sec
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D
3.85 μ sec
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Solution

The correct option is D 3.85 μ sec

When total internal reflection just takes place from lateral surface i = C i.e. 60=C
sin 60=sin C=1μμ=23

Time taken by light to traverse some distance in a medium t=μxc=23×1033×103=3.85 μ sec.


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