CBSE 2023 · Region 2 · Set 2 · Q27 · 3 marks
A ray of light is incident on a glass prism of refractive index $\displaystyle \mu$ and refracting angle A . If it just suffers total internal reflection at the other face, obtain a relation between the angle of incidence, angle of prism and critical angle.
Marking-scheme solution
Obtaining a relation between angle of incidence, angle of prism and critical angle
\[\begin{gathered}
\because \text { the light ray ji } \\
\therefore \angle r_{2}=\angle i_{c} \\
A=r_{1}+r_{2} \\
A=r_{1}+i_{c}
\end{gathered}
\] From Snell's law at surface AB
\[\begin{aligned}
& \sin i=\mu \cdot \sin r_{1} \\
& \sin i=\mu \cdot \sin \left(A-i_{c}\right)
\end{aligned}
\]
\[\begin{gathered}
\because \text { the light ray ji } \\
\therefore \angle r_{2}=\angle i_{c} \\
A=r_{1}+r_{2} \\
A=r_{1}+i_{c}
\end{gathered}
\] From Snell's law at surface AB
\[\begin{aligned}
& \sin i=\mu \cdot \sin r_{1} \\
& \sin i=\mu \cdot \sin \left(A-i_{c}\right)
\end{aligned}
\]Ray Optics and Optical InstrumentsTotal Internal ReflectionAnalyseshort_answerhard
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CBSE Class 12 Physics past-paper question from the 2023board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.