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InterviewSolution
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The width of a rectangular glass slab is 5 cm. From a point on its bottom surface, length rays are incident on its top face and after total reflection form a circle of light of radius 8 cm. What is the refractive index of the glass slab? |
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Answer» Solution :Let O be a bright point at the bottom face of the rectangular slab. Light RAYS staring from O return to the bottom face after total reflection from the upper face of the slab. As a result, a circle of light of RADIUS OA = OB = 8cm is formed on the bottom face. So angle of incidence on the upper face is `theta_(c)` (critical angle) [Fig. 2.60]. According to the figure `OP = sqrt(OC^(2) + PC^(2)) = sqrt((4)^(2) + (5)^(2)) = sqrt(41) cm` `therefore " " "refractive index"` `mu= (1)/(sintheta_(c)) = (1)/((OC)/(OP)) = (OP)/(OC) = (sqrt41)/(4) = 1.6` 
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