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Question

# The face PR of a prism QPR of angle 30o is silvered. A ray incident on face PQ at an angle of 45o as shown in the figure. The refracted ray undergoes reflected on face PR and retraces its path. The refractive index of the prism is

A
2
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B
3/2
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C
1.5
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D
1.33
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Solution

## The correct option is A √2From the image it is clear that,for the light to retrace its path, it should fall normally on the mirror.and for a normal fall on the mirror,900−r+900+300=1800r=300By snellls law,μairsin450=μsin300 μair=1μ=sin450sin300=2√2=√2Hence option A is the correct answer.

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