Page 50 - cbse-class-10-light-reflection-and-refraction

The earth's atmosphere contains a large number of molecules. These molecules
scatter light in a variety of ways. The air contains numerous tiny particles,
including dust and water vapour. As sunlight passes through the air, the shorter
blue light waves are reflected and refracted by the particles, whereas the longer
other colored light waves are unaffected and are not reflected by the water vapour
or dust in the air. As a result, blue is the most scattered color, which explains the
bluish color of the sky. At sunset or sunrise, the sunrays must travel long distances
through the atmosphere to reach us, and most of the blue light is scattered and does
not reach us. As a result, the sky and sun appear reddish at sunrise and sunset.

Tyndall Effect

The atmosphere of the Earth is a heterogeneous mixture of minute particles.
Smoke, tiny water droplets, dust particles suspended in the air, and air molecules
are examples of these particles. When a light beam collides with such air particles,
the path of the beam becomes visible. Likewise, the path of a light beam passing
through a true solution is not visible. However, its path becomes visible in a
colloidal solution where the particle size is relatively large. The Tyndall effect is
caused by the scattering of light by colloidal particles.

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