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Q136 (NDA-I/2025) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Geometrical optics Answer Verified

What happens when the sunlight travels through the Earth's atmosphere ?

Result
Your answer: —  Â·  Correct: A
Explanation

When sunlight travels through the Earth's atmosphere, it interacts with air molecules and fine particles that are smaller than the wavelength of visible light [1]. This interaction leads to Rayleigh scattering, where the magnitude of scattering is inversely proportional to the fourth power of the wavelength. Consequently, shorter wavelengths at the blue end of the spectrum are scattered much more strongly—approximately 16 times more than longer wavelengths like red [2]. This preferential scattering of blue light in all directions is what gives the sky its characteristic blue appearance. While red light has a wavelength about 1.8 times greater than blue light, it passes through the atmosphere with significantly less scattering [1]. During sunrise or sunset, the sunlight travels a longer atmospheric path, scattering away most blue light and leaving the longer red wavelengths to reach the observer [2].

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > 10.6.2 Why is the colour of the clear Sky Blue? > p. 169
  2. [2] https://spaceplace.nasa.gov/blue-sky/
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