Question

What is total internal reflection? Write necessary conditions for it.

Hint:

Total internal reflection can be observed in optical fibers and prisms when the angle of incidence exceeds the critical angle.

Answer 1

Step 1: Understanding Total Internal Reflection.
Total internal reflection occurs when a light ray traveling from a denser medium to a rarer medium is completely reflected back into the denser medium. This phenomenon only occurs when the angle of incidence exceeds a certain critical angle, and the light is traveling from a medium with a higher refractive index to one with a lower refractive index. Step 2: Conditions for Total Internal Reflection.
The necessary conditions for total internal reflection are: 1. The light must travel from a denser medium (higher refractive index) to a rarer medium (lower refractive index). 2. The angle of incidence must be greater than the critical angle, \( \theta_c \). The critical angle is given by: \[ \theta_c = \sin^{-1} \left( \dfrac{n_2}{n_1} \right) \] where \( n_1 \) is the refractive index of the denser medium and \( n_2 \) is the refractive index of the rarer medium. Step 3: Conclusion.
Total internal reflection is the phenomenon where the light is completely reflected back into the denser medium, and it occurs only when the angle of incidence is greater than the critical angle.