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Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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The colour of scattered light depends on the size of the scattering particles. Very fine particles scatter mainly which colour of light?
Yellow light
Blue light
Red light
Green light
Blue light
The scattering of light by particles with sizes smaller than the wavelength of visible light is known as Rayleigh scattering. According to this law, the intensity of scattered light is inversely proportional to the fourth power of its wavelength, meaning light with shorter wavelengths (like blue) is scattered much more effectively than light with longer wavelengths (like red) by very fine particles.
The scattering of light by particles with sizes smaller than the wavelength of visible light is known as Rayleigh scattering. According to this law, the intensity of scattered light is inversely proportional to the fourth power of its wavelength, meaning light with shorter wavelengths (like blue) is scattered much more effectively than light with longer wavelengths (like red) by very fine particles.
Think of it like a small pebble being thrown into a pond; smaller objects create more ripples and diffuse them across a wider area, whereas large objects might just cause a splash and settle, much like how small air molecules 'splash' the blue light across the sky.
B-I-G: Blue Is Greatest (scattered).
I∝λ41 — The intensity of scattered light is inversely proportional to the fourth power of the wavelength
The intensity of scattered light (I) follows Rayleigh's scattering law, expressed as I∝λ41. Very fine atmospheric particles, such as gas molecules and dust, have dimensions much smaller than the wavelength of incident sunlight. Because blue light has a shorter wavelength than red, it is scattered significantly more by these fine particles.
Rayleigh scattering occurs when particle size d≪λ.
Visible spectrum ranges from Violet (shortest λ) to Red (longest λ).
Blue light has a shorter wavelength than red light, leading to higher scattering.
Appearance of the clear blue sky
Reddish appearance of the Sun at sunrise and sunset
The sky appears blue because molecules in the air scatter blue light more efficiently than other colors.
Option A, C, and D are incorrect because their wavelengths are significantly longer than blue, leading to less efficient scattering by fine particles.
B is correct — Very fine particles scatter shorter wavelengths of light more effectively, which corresponds to blue light.
Always remember the relationship between wavelength and scattering: shorter wavelength equals more scattering, which is why the sky is blue and danger signals (long wavelength) are red.