Case: Read the passage and answer the question.
Total internal reflection is the reflection of light back into the denser medium at its interface with a rarer medium. For it to occur, light must travel from the denser medium towards the rarer medium, and the angle of incidence in the denser medium must be greater than the critical angle for the pair of media. The critical angle depends on the nature of the media and on the wavelength of light. It can be shown that \( \mu=1/\sin C \), where C is the critical angle.
Match List-I with List-II.
| List-I | List-II |
|---|---|
| (A) Angle of refraction when light falls at the critical angle | (I) 24.4° |
| (B) Critical angle of diamond | (II) 45° |
| (C) The critical angle of a prism that bends light by 90° must be less than | (III) 90° |
| (D) Angle through which a totally reflecting prism turns a ray to send it back | (IV) 180° |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A)-(III), (B)-(I), (C)-(II), (D)-(IV)
The critical angle is the angle of incidence in the denser medium for which the refracted ray just grazes the surface. Totally reflecting prisms use this effect to turn light without any loss through refraction.
(A) Angle of refraction when light falls at the critical angle — This matches (III) 90°. At the critical angle the refracted ray travels along the surface between the two media.
(B) Critical angle of diamond — This matches (I) 24.4°. Diamond has a very small critical angle, so light inside it is totally reflected many times.
(C) The critical angle of a prism that bends light by 90° must be less than — This matches (II) 45°. Inside such a prism the ray meets the slant face at 45°. Total internal reflection there needs a critical angle less than 45°.
(D) Angle through which a totally reflecting prism turns a ray to send it back — This matches (IV) 180°. With two total internal reflections the prism sends the ray back in the direction it came from.
NCERT (2026-27):
Total Internal Reflection – “The angle of incidence corresponding to an angle of refraction 90°, … is called the critical angle (ic) for the given pair of media. …”
Summary – “… Multiple internal reflections in diamond (ic ≅ 24.4°), totally reflecting prisms and mirage, are some examples of total internal reflection. …”
Total internal reflection in nature and its technological applications – “In the first two cases, the critical angle ic for the material of the prism must be less than 45°. …”
Total internal reflection in nature and its technological applications – “(i) Prism: Prisms designed to bend light by 90° or by 180° make use of total internal reflection …”