Total internal reflection can take place only, if
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → light goes from an optically denser medium to a rarer medium
Total internal reflection needs two conditions: the light must travel from a denser to a rarer medium, and the angle of incidence must be greater than the critical angle. Only then does the angle of refraction reach \( 90^\circ \) and beyond, so that no refracted ray exists.
\( \displaystyle \sin C = \frac{n_{\mathrm{rarer}}}{n_{\mathrm{denser}}} \lt 1 \)
NCERT (2026-27):
Total Internal Reflection – “When light travels from an optically denser medium to a rarer medium at the interface, it is partly reflected back into the same medium and partly refracted to the second medium. This reflection is called the internal reflection.”
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.”