1. Fish-eye view 2c
Fish-eye view – the scene above water is compressed into a cone of vertical angle = 2c.

2. 2c
Outside this cone, the scene underwater is reflected by total internal reflection.

3. Due to total internal reflection, the water surface looks like a mirror.

4. Total internal reflection in prisms
critical angle of glass = 41.1°
angle of incidence > 41.1°
glass-air boundary acts likes a plane mirror
45° – 90° – 45° prisms are often used in optical instruments to reflect light.
45°
90°
45°

5. angle of incidence > critical angle of glass
light rays parallel to normal
45°
angle of incidence > critical angle of glass
total internal reflection

6. Why prisms instead of plane mirrors are used in optical instruments?
Prismatic periscope
Why prisms instead of plane mirrors are used in optical instruments?

7. Multiple refraction and reflection occur. multiple images
multiple images formed
object
Multiple refraction and reflection occur.
multiple images

8. A 45º – 90º – 45º prism can turn light rays through 180°
Two glass prisms are used in a prismatic binocular to shorten its length.

9. used in single-lens reflex cameras
Pentaprisms
mirror
film
pentaprism
used in single-lens reflex cameras
Photographer sees exactly the same image that will form on film.

10. How does this kind of decorative lighting work?
Optical fibre
How does this kind of decorative lighting work?
Light is directed into the plastic pipes.
The light undergoes a series of total internal reflections.
The light exits at the other ends.

11. The structure of optical fibre
Optical fibres work on a similar principle.
1.25  10–4 m
glass inner core – a hair-thin glass fibre
8  10–6 m
glass outer cladding – smaller refractive index than the glass at inner core
protective coating
The structure of optical fibre

12. Video: Water light-pipe
Signals can be transmitted by optical fibres at a very high speed
(~ 2  108 m s–1).
optical fibre
light ray
Video: Water light-pipe

13. Uses of optical fibres:
carrying telephone signals, TV signals and computer data
transmitting images
stomach
Endoscopes enable doctors to see the inside of a human body.

14. The puddle of water disappears as the car proceeds. Why?
Mirage
On a hot day...
a puddle of water is seen

15. On a hot day...
heat up slower
observer
heat up faster

16. decreasing refractive index
On a hot day...
cool air
decreasing refractive index
observer
hot air

17. cool air hot air light gradually refracted from the normal observer
a puddle of water is seen
Video: Mirage

18. Total internal reflection in diamonds
A raw diamond appears to be rough stones.
A cut and shaped diamond sparkles.

19. Video: Disappearing watch
Most of the light that enters from above the diamond undergoes total internal reflection.
Video: Disappearing watch

20. Why does diamond jewellery usually have a more sparkling appearance than glass jewellery?
Diamonds have a larger refractive index.
They have a smaller critical angle.
More light entering the diamond jewellery undergoes total internal reflection.

21. That’s the end of Section 14.4
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Key Ideas
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