1. Total Internal Reflection
Can occur when light inside a glass block hits the edge at certain angles
Remember – if light hits the boundary between two media it will pass straight through
As you increase the angle of incidence, the ray gets bent
However – at a particular angle called the Critical Angle, something strange happens

2. N
REFRACTED RAY
The ray is refracted parallel to the edge of the block at the
Critical angle
TOTAL INTERNAL REFLECTION OF LIGHT
INCIDENT RAY

3. As we increase the angle of incidence
As the angle of incidence increases, the ray is now only reflected back inside the block
The edge of the block acts like a mirror
The ray does not pass out of the block
This is total internal reflection

4. But…. Total Internal Reflection only happens when………
The ray is travelling through a medium of higher refractive index and meets a boundary with a medium of lower refractive index (ie the light is slow moving and meets a medium where it would be fast moving)

5. So the 600 angle has total internal reflection

6. Internal Reflection
This occurs only when light travels from more dense to less dense media.

7. Notice that light is not able to get out of the water at an angles greater than 42°