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Q129
(NDA-I/2024)
Science & Technology › Basic Science (Physics, Chemistry, Biology)
Official Key
Which of the following statements with regard to the phenomenon of the primary rainbow formation by water droplets is/are correct ? 1. It involves refraction and one internal reflection of sunlight. 2. It involves refraction of sunlight only. 3. It is formed as the inner bow. 4. It may involve more than one internal reflection as well as refraction of sunlight. Select the answer using the code given below :
Explanation
A primary rainbow is formed through a specific sequence of optical phenomena: refraction as sunlight enters the water droplet, one internal reflection at the back of the droplet, and a final refraction as the light exits. This confirms that Statement 1 is correct.
- Statement 2 is incorrect because refraction alone cannot produce a rainbow; internal reflection is essential.
- Statement 3 is correct because, when both primary and secondary rainbows are visible, the primary rainbow is the inner bow (lower in the sky) with an angular radius of about 42°, whereas the secondary rainbow is the outer bow (about 51°).
- Statement 4 is incorrect for a primary rainbow; two internal reflections characterize a secondary rainbow.
Since Statements 1 and 3 are accurate, Option B is the correct answer.
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