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Difficulty: MediumPhysics Fundamentals and Everyday Applications

During sunrise and sunset, the Sun appears distinctly reddish when viewed from the Earth's surface. Which optical phenomenon is primarily responsible for this color phenomenon?

  1. A
    Total internal reflection of light rays passing through atmospheric layers of varying temperature gradients
  2. Rayleigh scattering of light by atmospheric molecules, where shorter wavelengths are scattered away more than longer wavelengthsAnswer
  3. C
    Atmospheric refraction caused by the continuous change in the refractive index of air layers
  4. D
    Diffraction of light waves around microscopic suspended aerosols and water droplets

Answer

Rayleigh scattering of light by atmospheric molecules, where shorter wavelengths are scattered away more than longer wavelengths
During sunrise and sunset, sunlight travels through a longer path in the Earth's atmosphere. According to Rayleigh's law, the scattering of light is inversely proportional to the fourth power of its wavelength. Consequently, shorter wavelengths such as blue and violet are scattered in all directions and lost from the direct line of sight, while longer wavelengths such as red pass through with minimal scattering and reach the observer's eyes.

Step-by-Step Solution

1
Analyze the path length of sunlight through the Earth's atmosphere during sunrise and sunset.
Near the horizon, sunlight travels a significantly longer path through atmospheric layers than at noon.
The slant angle requires light to pass through more air mass and scattering centers.
2
Apply Rayleigh's law of scattering.
Scattering intensity is inversely proportional to the fourth power of wavelength (I∝1λ4I \propto \frac{1}{\lambda^4}).
Shorter wavelengths (blue and violet) are scattered much more strongly than longer wavelengths (red and orange).
3
Determine which wavelengths reach the observer.
Blue light is scattered out in all directions, while unscattered red light passes directly to the observer.
Red light has a longer wavelength and undergoes minimal scattering over the long atmospheric path.

Key Concept

Rayleigh Scattering of Light
Estimated Time:1m 0s
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Topics

Physics Fundamentals and Everyday Applications

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