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

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

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

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°

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

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

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

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

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.

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.

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

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

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.

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

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

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

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

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

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

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.

That’s the end of Section 14.4 Check Point Key Ideas Previous Page Exit