A ray of laser of a wavelength 630 nm is incident at an angle of 30 °… | JEE Main 2021 (25 Jul, Shift 1)

Q33JEE Main 2021 · 25 JUL · SHIFT 1Medium

Total Internal Reflection

A ray of laser of a wavelength 630 nm is incident at an angle of 30 ${}^\circ$ at the diamond-air interface. It is going from diamond to air. The refractive index of diamond is 2.42 and that of air is 1. Choose the correct option.

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Answer: (c)

Critical angle for diamond-air: $\sin C = \frac{1}{2.42} \approx 0.413 \Rightarrow C \approx 24.4^\circ$ .
The angle of incidence $30^\circ > C$ , so the light is totally internally reflected.
(Snell's law would need $\sin r = 2.42\times0.5 = 1.21 > 1$ , which is impossible.)
So the answer is (c) refraction is not possible.

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Total Internal Reflection question from JEE Main 2021 (25 Jul, Shift 1)

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