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WBJEE 2014 Physics Solved Paper
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© examsnet.com
Question : 51
Total: 60
A glass slab consists of thin u iform layers of progressively decreasing refractive indices RI (see figure) such that theRI of any layer is μ-mΔμ. Here μ and Δμ denote the RI of 0th layer and the difference in RI between any two consecutivelayers, respectively. The integer m = 0, 1, 2, 3..... denotes the numbers of the successive layers. A ray of light fromthe 0th layer enters the 1st layer at an angle of incidence of 30°. After undergoing the mth refraction, the ray emergesparallel to the interface. If μ = 1.5 and Δμ = 0.015, the value of m is
20
30
40
50
Validate
Solution:
By Snell’s law, μ sin i = constant,1.5 sin 30° = (μ – mΔμ) sin 90°
3
2
×
1
2
= (1.5 - m × 0.15) × 1
∴ m = 50
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