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Question
Answer the following question in detail.
Explain the formation of a primary rainbow. For which angular range with the horizontal is it visible?
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Solution
- A ray AB incident from Sun (white light) strikes the upper portion of a water drop at an incident angle i.
- On entering into the water, it deviates and disperses into constituent colours. The figure shows the extreme colours (violet and red).
Formation of primary rainbow - Refracted rays BV and BR strike the opposite inner surface of water drop and suffer internal reflection.
- These reflected rays finally emerge from V′ and R′ and can be seen by an observer on the ground.
- For the observer, they appear to be coming from the opposite side of the Sun.
- Minimum deviation rays of red and violet colour are inclined to the ground level at θR = 42.8° ≈ 43° and θV = 40.8 ≈ 41° respectively. As a result, in the rainbow, the red is above and violet is below.
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| Case study: Mirage in deserts |
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To a distant observer, the light appears to be coming from somewhere below the ground. The observer naturally assumes that light is being reflected from the ground, say, by a pool of water near the tall object. Such inverted images of distant tall objects cause an optical illusion to the observer. This phenomenon is called mirage. This type of mirage is especially common in hot deserts. Based on the above facts, answer the following question : |
A diver at a depth 12 m inside water `(a_(µω) = 4/3)` sees the sky in a cone of semi-vertical angle
The sky would appear red instead of blue if
A short pulse of white light is incident from air to a glass slab at normal incidence. After travelling through the slab, the first colour to emerge is ______.
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- angle made at the eye by the scattered rays with respect to the incident light of the sun lies between approximately 42° and 50°.
