1. 4.5 What causes Total Internal Reflection?

4. Total Internal Reflection …
… is the condition in which light cannot escape the medium because the angle of incidence is larger than the critical angle.
So all the light stays in the medium
When the angle of incidence is greater than 90o, total internal reflection results.

6. Total Internal Reflection
normal
air
refracted ray R
water i r
incident ray
reflected ray
When light moves from a more dense to less dense medium it speeds up which increase the angle of refraction (compared to the angle of incidence)

7. Total Internal Reflection
normal
air
refracted ray R
water r i
incident ray
reflected ray
As the angle of incidence increases the angle of reflection continues to increase at a greater rate

8. Total Internal Reflection
normal
air
refracted ray R
water r i
incident ray
reflected ray
As the angle of incidence increases the angle of reflection continues to increase at a greater rate

9. Total Internal Reflection
normal
air
refracted ray R
water i r
incident ray
reflected ray
Eventually the angle of incidence reaches 90o (the critical angle) and all light is reflected internally

10. Total Internal Reflection
normal
air
water i r
incident ray
reflected ray
At 90o and beyond, all light is internally reflected, none escapes.

11. Fibre Optics
Optical fibres are made of tiny glass fibre cores that are coated with a less dense material (called the cladding)
When light enters the core it is internally reflected

12. Fibre Optics
The core and cladding are protected by more material (usually plastic)
Optical fibres are more efficient at carrying electrical signals that copper wire
Not affected by electrical storms
Carry signals over longer distances
Carry more signals that copper wire
Smaller and lighter (and glass is plentiful and cheap!)