A ray of light is incident normally on a prism $ABC$ of refractive index $\sqrt{2}$, as shown in the figure. After it strikes face $AC$, it will:

(D) undergo total internal reflection

(B) just graze along the face $AC$

(C) refract and go out of the prism

CBSE Class 12 · 2024 · Geometrical OpticsMultiple Choice

A ray of light is incident normally on a prism

A B C

of refractive index

2

, as shown in the figure. After it strikes face

A C

, it will:

Answer: (D)

The ray enters normally and strikes

A C

4 5^{\circ}

. Critical angle

θ_{c} = sin^{- 1} \frac{1}{2} = 4 5^{\circ}

. Since the incidence equals/exceeds

θ_{c}

(here grazing-to-TIR with

μ sin 4 5^{\circ} = \frac{2}{2} \cdot 2 = 1

), the ray undergoes \emph{total internal reflection}.

CBSE Class 12 Board · 2024 · Single correct option