a. If the angle of incidence and angle of emergence of a light ray falling on a glass slab are i and e respectively, prove that, i = e. 79
The phenomenon of rainbow can be explained as follows:
  1. For some time after the rain stops, the atmosphere contains a large number of tiny water droplets.
  2. When the sunlight is incident on a water droplet, there is (i) refraction and dispersion of light as it passes from air to water (ii) internal reflection of light inside the droplet and (iii) refraction of light as it passes from water to air.
  3. The sunlight is a mixture of seven colours: violet, indigo, blue, green, yellow, orange, and red. The refractive index of water is different for different colours. It is maximum for violet colour and minimum for red colour. Hence, there is dispersion of light as it passes from air to water.
  4. The combined action of different water droplets, acting like tiny prisms, is to produce a rainbow with red colour at the outer side and violet colour on the inner side the remaining five colours lie between these two.
  5. The rainbow is seen when the sun is behind the observer and the water droplets are in front.
3 Marks
b. A raibow is the combined effect of the refraction, dispersion, and total internal reflection of light. 79
The phenomenon of rainbow can be explained as follows:
  1. For some time after the rain stops, the atmosphere contains a large number of tiny water droplets.
  2. When the sunlight is incident on a water droplet, there is (i) refraction and dispersion of light as it passes from air to water (ii) internal reflection of light inside the droplet and (iii) refraction of light as it passes from water to air.
  3. The sunlight is a mixture of seven colours: violet, indigo, blue, green, yellow, orange, and red. The refractive index of water is different for different colours. It is maximum for violet colour and minimum for red colour. Hence, there is dispersion of light as it passes from air to water.
  4. The combined action of different water droplets, acting like tiny prisms, is to produce a rainbow with red colour at the outer side and violet colour on the inner side the remaining five colours lie between these two.
  5. The rainbow is seen when the sun is behind the observer and the water droplets are in front.
3 Marks
Watch Video (1:16):

A video by Merit Nation explaining advanced sunrise and delayed sunset:
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