1. Refraction Phenomena including Total Internal Reflection
SNC2D

2. Refraction Effects
Refraction effects produce a number of interesting observable phenomena

3. Refraction Effects
Refraction effects produce a number of interesting observable phenomena
E.g. objects in water may appear to be displaced

4. The Broken Pencil
If we look at an object in a different medium, we will see an image of the object along the line of sight of the rays that are refracted to us.

5. Apparent Depth
Similarly, an object underwater will appear to be at a different depth than its actual depth:

6. Total Internal Reflection
But more interesting than the refraction of light rays is the failure of light rays to refract

7. Total Internal Reflection (TIR)
Recall that if a ray is travelling from a less-dense material to a more-dense material, it will bend towards the normal and if travelling from a more-dense material to a less-dense material it will bend away:

8. Total Internal Reflection (TIR)
So for the case of the ray travelling from the more-dense material to the less-dense material, there must exist some critical incident angle such that the ray will refract at 90o from the normal (along the boundary).

9. Total Internal Reflection (TIR)
If the light is incident at an angle larger than this critical angle qc, total internal reflection will occur.

10. Total Internal Reflection (TIR)
If the light is incident at an angle larger than this critical angle qc, total internal reflection will occur.

11. Total Internal Reflection (TIR)
If the light is incident at an angle larger than this critical angle qc, total internal reflection will occur.

12. Total Internal Reflection (TIR)
If the light is incident at an angle larger than this critical angle qc, total internal reflection will occur.
And remember that nr will be 1.0 if the second medium is air.

13. TIR: Example
When light is travelling through glass into air, the total internal reflection will occur at a critical angle of 42o. Find the index of refraction of the glass.

14. TIR: Example
When light is travelling through glass into air, the total internal reflection will occur at a critical angle of 42o. Find the index of refraction of the glass.

15. TIR: Example
When light is travelling through glass into air, the total internal reflection will occur at a critical angle of 42o. Find the index of refraction of the glass.

16. TIR: Example
When light is travelling through glass into air, the total internal reflection will occur at a critical angle of 42o. Find the index of refraction of the glass.

17. Your Task
When finding the critical angle (and therefore the index of refraction) for various materials, be careful!
Note that partial reflection will occur at angles less than the critical angle.

18. TIR: An Application
Optical fibres are based entirely on the principle of TIR. An optical fibre is a flexible strand of glass. With a straight or smoothly bending fibre, the light will hit the wall at an angle higher than the critical angle and will all be reflected back into the fibre so that no light will be lost.

19. TIR: Mirages
Air of different densities will have different ns and light rays can reflect within the air, resulting in mirages and looming artifacts.

20. TIR: Mirages
Air of different densities will have different ns and light rays can reflect within the air, resulting in mirages and looming artifacts.

21. TIR: Mirages
Air of different densities will have different ns and light rays can reflect within the air, resulting in mirages and looming artifacts.

22. Dispersion
Different frequencies (colours) of light actually refract at different angles.
This is called dispersion and is especially apparent when white light is passed through a prism.

23. Dispersion in Water Droplets
Dispersion and total internal reflection can occur in water droplets in the air:

24. Dispersion in Water Droplets
which may result in rainbows: