Lesson: Critical Angle for Total Internal Reflection Physics • 9th Grade

In this lesson, we will learn how to relate the paths of refracted and internally reflected light rays to the refractive indices of media they travel in.

Lesson Plan

Students will be able to

calculate , the critical angle for light rays traveling in a medium of refractive index at a boundary with a medium of refractive index , using , where ,
rearrange to determine unknown refractive indices,
interpret diagrams of light rays taking different paths to infer the relations between incident and refracted angles and between the refractive indices of media.

Lesson Presentation

Lesson Video

Lesson Explainer

Lesson Worksheet

Q1:

Which of the following formulas correctly shows the relation between the critical angle for total internal reflection for a light ray, the refractive index of the substance the light is propagating in, and the refractive index of the substance when the light is reflected from its surface?

Q2:

What is the critical angle for a light ray traveling in water with a refractive index of 1.33 that is incident on the surface of water above which air is with a refractive index of 1.00? Answer to the nearest degree.

Q3:

What is the critical angle for a light ray traveling in water with a refractive index of 1.33 that is incident on the surface of water above which there is ice with a refractive index of 1.31? Answer to the nearest degree.