The necessary conditions for total internal reflection are(A) Light m…

The correct answer is Option (3) → (A) and (D) only

Total internal reflection happens only when light going from a denser to a rarer medium meets the surface at an angle larger than the critical angle \( i_c \), where \( \sin i_c = n_2/n_1 \).

(A) Light must travel from denser to rarer medium. — Correct. Only then does the refracted ray bend away from the normal, so that it can reach \( 90^\circ \) and disappear.

(B) The angle of incidence in the denser medium must be less than the critical angle for the two media. — Incorrect. For \( i \lt i_c \) the light is partly refracted into the rarer medium; there is no total reflection.

(C) Light must travel from rarer to denser medium. — Incorrect. Going into a denser medium the ray bends towards the normal, so a refracted ray always exists.

(D) The angle of incidence in the denser medium must be greater than the critical angle for the two media. — Correct. For \( i \gt i_c \), Snell's law would need \( \sin r \gt 1 \), so no refracted ray exists and all the light is reflected.

NCERT (2026-27):
Total Internal Reflection – “… When a ray of light enters from a denser medium to a rarer medium, it bends away from the normal, for example, the ray AO₁B in Fig. 9.11.”

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.”

Total Internal Reflection – “… For values of i larger than i_c, Snell’s law of refraction cannot be satisfied, and hence no refraction is possible.”