Question

Define the critical angle and state the conditions required for Total Internal Reflection (TIR).

Hint:

TIR occurs only when light goes from denser to rarer medium and the angle of incidence exceeds the critical angle.

Answer 1

Critical Angle:
The critical angle is the angle of incidence in the denser medium for which the angle of refraction in the rarer medium becomes 90°. At this angle, the refracted ray just grazes along the boundary between the two media.

It is represented by C and is given by the relation:
sin C = n₂ / n₁

Where n₁ is the refractive index of the denser medium and n₂ is the refractive index of the rarer medium (n₁ > n₂).

Conditions for Total Internal Reflection (TIR):

1. The light must travel from a denser medium to a rarer medium (for example, from glass to air).

2. The angle of incidence in the denser medium must be greater than the critical angle.

When both these conditions are satisfied, the refracted ray does not emerge into the second medium. Instead, it is completely reflected back into the denser medium. This phenomenon is called Total Internal Reflection.