Total internal reflection occurs when incoming light travelling through a medium strikes the boundary with a second medium at angles greater than a certain critical angle with the result that no light crosses the boundary and so all the light is reflected back into the medium.
- Internal refraction only takes place if the refractive index is lower for the medium on the other side of the boundary.
- The critical angle is the angle of incidence above which internal reflection occurs.
- The critical angle is measured with respect to the normal.
- The normal is an imaginary line drawn in a ray diagram perpendicular to, so at a right angle to (900), to the boundary between two media.
Related diagrams
Each diagram below can be viewed on its own page with a full explanation.
