Consider the following statements, where \(i_c\) is the critical angle for a pair of media:
(A) When light goes from a denser medium to a rarer medium, the refracted ray bends towards the normal.
(B) In total internal reflection, no light is transmitted into the rarer medium.
(C) The critical angle is the angle of incidence for which the angle of refraction is \(90^\circ\).
(D) The refractive index of the denser medium with respect to the rarer medium is equal to \(\sin i_c\).
Which of the above statements are incorrect?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A) and (D) only
Light going from a denser to a rarer medium bends away from the normal. At the critical angle the refracted ray grazes the surface. For larger angles, all the light is reflected back.
(A) When light goes from a denser medium to a rarer medium, the refracted ray bends towards the normal. — Incorrect statement. The refracted ray bends away from the normal, so the angle of refraction is larger than the angle of incidence.
(B) In total internal reflection, no light is transmitted into the rarer medium. — Correct statement. Beyond the critical angle no refraction is possible. All the light stays in the denser medium.
(C) The critical angle is the angle of incidence for which the angle of refraction is \(90^\circ\). — Correct statement. This is the definition of the critical angle. At this angle the refracted ray grazes the surface.
(D) The refractive index of the denser medium with respect to the rarer medium is equal to \(\sin i_c\). — Incorrect statement. The refractive index of the denser medium with respect to the rarer medium is \( n_{12}=1/\sin i_c \). The value \( \sin i_c \) gives \( n_{21} \), which is less than 1.
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, …”
Total Internal Reflection – “… In total internal reflection, on the other hand, no transmission of light takes place.”
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. …”
Total Internal Reflection – “The refractive index of denser medium 1 with respect to rarer medium 2 will be n12 = 1/sin ic. …”