Three rays of light, namely red (R), green (G) and blue (B) are… | JEE Main 2021 (18 Mar, Shift 2)

Q35JEE Main 2021 · 18 MAR · SHIFT 2Medium

Total Internal Reflection

Three rays of light, namely red (R), green (G) and blue (B) are incident on the face PQ of a right angled prism PQR as shown in the figure.

The refractive indices of the material of the prism for red, green and blue wavelength are 1.27, 1.42 and 1.49 respectively. The colour of the ray(s) emerging out of the face PR is:

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Answer: (d)

The rays enter PQ normally and meet PR at an angle of incidence $45^\circ$ (isosceles right prism).
A ray comes out of PR only if $\mu < \frac{1}{\sin45^\circ} = \sqrt{2} \approx 1.414$ .
Red $1.27 < 1.414$ comes out; green $1.42$ and blue $1.49$ are totally reflected.
So the answer is (d) red.

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Total Internal Reflection question from JEE Main 2021 (18 Mar, Shift 2)

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