Page 253 - text book form physics kssm 2020

Chapter 6
Light and Optics
Natural Phenomena that Involve Total Internal Reflection

Formation of rainbow
Formation of rainbow is a phenomenon caused by refraction, dispersion and total internal
reflection when light passes through water droplets in the air. Figure 6.22 shows the formation
1 When white light from the Sun enters water
of rainbow.
droplets, the light experiences refraction and
1 disperses into different colours.
Raysys ffrom
the e Sunn 2
2 All these different colours experience total internal
reflection on the surface of the water droplets.

3
Pu
Purrpplelee
3 Light rays reflected experience refraction and
dispersion again when moving from water to air.
O Obseeeervr er 4
Re
Redd 4
Colours of the rainbow are seen by the observer.

Figure 6.22 Formation of rainbow
Mirage
On a hot and bright day, a car driver sees the blurry image of a puddle of water on the surface
of the road ahead. When he gets nearer to the puddle of water, he discovers that the puddle of
water does not actually exist. This natural phenomenon is known as mirage which is caused by
refraction and total internal reflection of light. Figure 6.23 shows the process of formation
of mirage.
Cloud
1 Observer Cold air 1
Layers of air above the road have different (denser)
optical densities. The layer of air just above the
road surface is hotter than the upper layers. 3 Hot air
The layer of hot air has smaller optical density 2 (less dense)
than cold air.
2
Light which travels from the upper layer to the lower Road
layer are gradually refracted away from the normal.
When the angle of incidence is greater than the critical Image of cloud
angle of air, total internal reflection occurs.
3 Reflected light rays are then gradually refracted towards the normal

and reach the eyes of the observer. The observer will see the image of a
cloud as a puddle of water on the road surface.

Figure 6.23 Formation of mirage

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