Let the refractive index of a denser medium with respect to a rarer… | JEE Main 2017 (8 Apr, Shift 1)

Q46JEE Main 2017 · 8 APR · SHIFT 1Medium

Total Internal Reflection

Let the refractive index of a denser medium with respect to a rarer medium be n12 and its critical angle be θC. At an angle of incidence A when light is travelling from denser medium to rarer medium, a part of the light is reflected and the rest is refracted and the angle between reflected and refracted rays is 90°. Angle A is given by:

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Answer: (d)

Snell's law (denser to rarer): $n_{12}\sin A = \sin r$ .
Reflected and refracted rays are perpendicular, so $A + r = 90^\circ$ and $\sin r = \cos A$ .
$n_{12}\sin A = \cos A \Rightarrow \tan A = \frac{1}{n_{12}} = \sin\theta_C$ .
So the answer is (d) $A = \tan^{-1}(\sin\theta_C)$ .

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Total Internal Reflection question from JEE Main 2017 (8 Apr, Shift 1)

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