Cambridge O Level Physics · Syllabus 5054 · Waves
Total Internal Reflection
What is Total Internal Reflection?
Total internal reflection is the complete reflection of light back into the denser medium at a boundary; it occurs only when light travels from a medium of higher refractive index to one of lower refractive index and the angle of incidence is greater than the critical angle.
This definition is part of the Waves chapter in Cambridge O Level Physics.
Common mistakes with Total Internal Reflection
- 12. “Total internal reflection occurs at the critical angle.” Why wrongAt exactly \(c\) a refracted ray still exists — it travels along the boundary at 90° to the normal. CorrectTotal internal reflection needs the angle of incidence to be strictly greater than \(c\). Say this“Total internal reflection occurs when the angle of incidence is greater than the critical angle.” CheckWater has \(c = 49^\circ\). A ray inside the water strikes the surface at 49°. What happens?
Last reviewed Syllabus 2026-2028