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  4. A light ray is incident perpendicular to one face of a 90° prism and is totally internally reflected at the glass-air interface. If the angle of reflection is 45°, we conclude that the refractive index n

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Q. A light ray is incident perpendicular to one face of a $90^{\circ}$ prism and is totally internally reflected at the glass-air interface. If the angle of reflection is $45^{\circ}$, we conclude that the refractive index $n$Physics Question Image

AIEEEAIEEE 2004Ray Optics and Optical Instruments

Solution:

Angle of incidence $i > C$ for total internal reflection.
Here $i = 45^{\circ}$ inside the medium.
$\therefore \quad45^{\circ} > sin^{-1}\left(1/n\right)$
$\Rightarrow n > \sqrt{2}.$