The diagrams show two glass blocks in air. For the rays of light shown, the critical angle for the glass/air boundary is 42°. A ray of light is shown approaching the boundary in each case, with the angle of incidence labelled. Two possible labelled directions in which each ray might travel after reaching the boundary are also shown.

Which line in the table correctly shows the direction taken by most or all of the light and also states whether total internal reflection (T.I.R.) will occur?

Answer:

11) C

Source: Wikipedia
https://en.wikipedia.org/wiki/Total_internal_reflection#/media/File:RefractionReflextion.svg

-When angle of incidence is lower than critical angle, refraction occurs. and light leaves the medium.

-When angle of incidence is equal to critical angle, the light travels along the boundary of the two mediums.

-When angle of incidence is greater than critical angle, total internal reflection occurs. Angle of incidence is equal to angle of reflection.

Diagram 1:
The angle of incidence (40˚) is less than the critical angle given in the question (42˚). Since it is lower than the critical angle, the light will refract out of the glass block. Therefore the passage would be P. Since it refracts, there is no Total Internal Reflection (TIR).

Diagram 2:
Now, you may be confused that why TIR does not occur in this case. A condition for TIR is that light must travel from a dense medium to a less dense medium (glass to air and not air to glass).

TIR does not occur when light travel from air to glass. Instead, light refracts, meaning that it follows the S path.

Direction in diagram 1: P
TIR in diagram 1: No

Direction in Diagram 2: S
TIR in diagram 2: No

Hence, the answer is C.