Light - TIR - Find the refractive index of the liquid

Answer: Option D

For total internal reflection TIR to occur, two conditions must be present:

1. light must be travelling from a optically denser medium towards an optically less dense medium.

2. the angle of incidence i is greater than the critical angle c

Key things to take note:

1. The angles stated on the diagram are not angles of incidence. Angle of incidence is between the incident ray and the normal.

2. The diagram on the left is TIR as all the light is being internally reflected within the optical denser medium, which is the liquid.

3. The diagram on the right with refracted ray along the boundary, i.e. angle of refraction is 90 degrees, the angle of incidence now is also the critical angle of the liquid.

Refer to the video explanation