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Question
Answer the following question in detail.
Explain the formation of a secondary 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 lower 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 secondary rainbow - Refracted rays BV and BR finally emerge the drop from V' and R' after suffering two internal reflections and can be seen by an observer on the ground.
- Minimum deviation rays of red and violet colour are inclined to the ground level at θR ≈ 51° and θV ≈ 53° respectively. As a result, in the rainbow, the violet is above and red is below.
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