A ray of light enters from a denser medium to a rarer medium. The refracted ray is bent so much away from the normal that it grazes the surface at the interface between the two media. This will happen
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → when the angle of incidence is equal to the critical angle
The critical angle is the angle of incidence in the denser medium for which the angle of refraction is \( 90^{\circ} \), so the refracted ray just grazes the interface.
\( n_{1}\sin i_{c} = n_{2}\sin90^{\circ} \Rightarrow \sin i_{c} = n_{2}/n_{1} \)
Why the other options are incorrect
Option (1) when the angle of incidence is less than the critical angle — Incorrect. For an angle smaller than the critical angle, the ray does go into the rarer medium, bent away from the normal, but at less than \( 90^{\circ} \).
Option (3) when the angle of incidence is greater than the critical angle — Incorrect. For an angle greater than the critical angle, no refracted ray exists; the light undergoes total internal reflection.
Option (4) for all angles of incidence — Incorrect. The angle of refraction depends on the angle of incidence, so grazing emergence happens at one angle only.
NCERT (2026-27):
Total Internal Reflection – “… The angle of incidence corresponding to an angle of refraction 90°, say ∠AO3N, is called the critical angle (ic) for the given pair of media.”