Dispersion And Scattering

Question

During the daytime the clear sky overhead appears blue to observers on the ground, and a curious learner wants to know the reason behind this colour.

RankGuru · Accepted Answer

NCERT explains the blue sky through Rayleigh scattering, in which the intensity of light scattered by tiny air molecules is inversely proportional to the fourth power of the wavelength, $I\propto\frac{1}{\lambda^4}$. Because blue light has a shorter wavelength than red, it is scattered far more strongly, roughly by a factor of several times, so scattered blue light reaches the eye from every part of the sky. This is why the daytime sky glows blue while the direct sun, with its blue removed, looks slightly yellowish. The option that blue travels faster is wrong because scattering, not speed differences, governs sky colour, and all colours travel at essentially the same speed in air. The option about total absorption is wrong because the atmosphere is largely transparent to visible light, not selectively absorbing. The option about water vapour reflection is wrong because the effect persists even in dry clear air, so molecular scattering, not vapour, is responsible. As stated in NCERT Class 12, Chapter 9, the strong wavelength dependence of Rayleigh scattering explains both the blue sky and red sunsets. A consistency check confirms that at sunset the long path scatters away blue, leaving red, which agrees with the same law.

Dispersion And Scattering

Select the correct option:

🔒 Solution Hidden from View

More optics Practice Questions

An astronomer wants a telescope to distinguish two closely spaced stars more clearly, and a student ...

A patient can see distant objects clearly but struggles to focus on nearby print, and an optometrist...

A ray of light passes through a rectangular glass slab with parallel faces immersed in air, and a st...

A compound microscope achieves high magnification by combining two convex lenses, and a laboratory s...

In a Young's double slit setup, light of wavelength 600 nm illuminates slits separated by 1 mm and t...

An astronomical telescope in normal adjustment uses an objective of focal length 100 cm and an eyepi...

An illuminated object 2 cm tall is placed before a convex lens that produces a real image 6 cm tall ...

A biconvex lens is ground from glass of refractive index 1.5 with both surfaces having a radius of m...

Unpolarized light of intensity I0 passes first through an ideal polarizer and then a second polarize...

A thin converging lens forms a sharp image on a screen placed 40 cm away when a candle stands 40 cm ...

Two thin lenses of powers +5 D and -2 D are placed in contact along the same axis, and an optician w...

Two independent ordinary light bulbs placed side by side never produce a stable interference pattern...

About This Question

Solution