Question

The observation made by Swarali while doing the experiment is given below. Based on these write answers to the questions:

Swarali found that the light ray travelling from the denser medium to rarer medium goes away from the normal. If the angle of incidence (i) is raised by Swarali, the angle of refraction (r) went on increasing. However, after certain value of the angle of incidence the light ray is seen to return back into the denser medium.

Questions:

1. What is the specific value of∠i called?
2. What is the process of reflection of incident rays into denser medium called?
3. Draw the diagrams of three observations made by Swarali.

Answer 1

1) The specific value of ∠i called the critical angle.
2) Total internal reflection.

3)

Observation 1: When i₁ < i_C, then refraction takes place and refracted ray moves away from normal i.e., r₁ > i₁.

Observation 2: When i₁ = i_C then refracted ray becomes perpendicular to normal i.e., r₂ = 90. 

Observation 3: When i₃ > i_C then total internal reflection takes place i₃ = r₃, where, i_C is the critical angle.