Identify the correct statement(s) among the following:
(A) When a light ray enters a denser medium, the speed of the ray decreases.
(B) In the phenomenon of total internal reflection, refraction also occurs in the denser medium.
(C) In the process of total internal reflection, the laws of reflection doesn't follow.
(D) When a ray is totally internally reflected, its energy doesn't change.
Choose the correct answer from the following options:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A) and (D) only
In total internal reflection the angle of incidence in the denser medium exceeds the critical angle, so no refracted ray exists and all the light is reflected back.
(A) When a light ray enters a denser medium, the speed of the ray decreases. — Correct. An optically denser medium has a larger refractive index, and \( v = c/n \).
(B) In the phenomenon of total internal reflection, refraction also occurs in the denser medium. — Incorrect. Beyond the critical angle there is no refracted ray; that is exactly why the reflection is called total.
(C) In the process of total internal reflection, the laws of reflection doesn't follow. — Incorrect. The reflected ray still lies in the plane of incidence and the angle of reflection equals the angle of incidence.
(D) When a ray is totally internally reflected, its energy doesn't change. — Correct. No light is lost to a refracted ray, so the whole energy is carried by the reflected ray.
NCERT (2026-27):
Total Internal Reflection – “… If the angle of incidence is increased still further (e.g., the ray AO4), refraction is not possible, and the incident ray is totally reflected. This is called total internal reflection. When light gets reflected by a surface, normally some fraction of it gets transmitted. The reflected ray, therefore, is always less intense than the incident ray, howsoever smooth the reflecting surface may be. In total internal reflection, on the other hand, no transmission of light takes place.”