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A ray of light is incident on a right angled isosceles prism parallel to its base as shown in the figure. Refractive index of the material of the prism is $\sqrt{2}$. Then. which of the following statement(s) is/are true? 
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The refiection at $P$ is total internal., The ray emerging at $R$ is parallel to the ray incident at $S .$
Critical angle $\theta_{C}=\sin ^{-1}\left(\frac{1}{\sqrt{2}}\right)=45^{\circ}$
Snell's law at points, $\left(\because n_{1} \sin \theta_{1}=n_{2} \sin \theta_{2}\right)$
$1 \sin 45^{\circ}=\sqrt{2} \sin \theta$
$\therefore \quad \theta=30^{\circ}$
At $P \because$ incidence angle at $P=75^{\circ}>\theta_{C}$
$\therefore$ TIR at point $P$
At $Q \because$ incidence angle at $Q=15^{\circ} < \theta_{C}$
$\therefore$ Partial reflection and refraction at $Q .$ As $S P \| Q R$, emergent ray at $R$ is parallel to incid,
ray at $S$.
$\therefore$ Net deviation $=180^{\circ}$
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