Lesson Plan: Critical Angle for Total Internal Reflection Physics

This lesson plan includes the objectives, prerequisites, and exclusions of the lesson teaching students how to relate the paths of refracted and internally reflected light rays to the refractive indices of the media they travel in.


Students will be able to

  • calculate πœƒ, the critical angle for light rays traveling in a medium of refractive index π‘›οŠ§ at a boundary with a medium of refractive index π‘›οŠ¨, using sinπœƒ=π‘›π‘›οŠ¨οŠ§, where 𝑛<π‘›οŠ¨οŠ§,
  • rearrange sinπœƒ=π‘›π‘›οŠ¨οŠ§ 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.


Students should already be familiar with

  • the behavior of light rays incident on media boundaries at angles less than, equal to, and greater than the critical angle for the media boundary,
  • Snell’s law.


Students will not cover

  • mechanisms to explain why total internal reflection occurs at the critical angle.

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.