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NEET 2018 · Prism, Dispersion & Scattering

Prism, Dispersion & Scattering question from NEET 2018

Q76NEET 2018Medium

Prism, Dispersion & Scattering

The refractive index of the material of a prism is $\sqrt{2}$ and the angle of the prism is 30°. One of the two refracting surfaces of the prism is made a mirror inwards, by silver coating. A beam of monochromatic light entering the prism from the other face will retrace its path (after reflection from the silvered surface) if its angle of incidence on the prism is

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Answer: (b)

Retracing needs normal incidence on the silvered face, so the refraction angle at the first face is $r = A = 30^\circ$ .
$\sin i = \mu\sin r = \sqrt{2}\times\frac{1}{2} = \frac{1}{\sqrt{2}}$
So the answer is (b) $45^\circ$ (printed as 450).

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