Ray Optics

Class XII Physics : RAY OPTICS

CONCAVE MIRROR:  Image characteristics for different object positions:

Concave mirror image positions

CONVEX MIRROR: Image characteristics for different object positions:

Convex mirror image positions

Q: Why does the sky look  blue?

Answer: White light coming from the sun gets scattered by the tiny particles of the atmosphere. As the size of these tiny particles is much less than the wavelength of light, as per Rayleigh scattering,  the intensity of the scattered light varies inversely as the fourth power of wavelength. As the wavelength of blue colour is almost half of red, the intensity of blue colour becomes much more than red in the scattered light. This scattered light, rich in blue colour, reaches our eyes and so the sky looks blue.

Q: Why do clouds look  white?

Answer: White light coming from the sun gets scattered by the tiny particles of the atmosphere. As the size of the particles in the cloud (raindrops, large dust or ice particles) is much more than the wavelength of light, all wavelengths are scattered equally. So clouds are generally white.

Q: Why do the sun look reddish at sunrise or sunset?

Answer: At sunrise or sunset, white light coming from the sun has to travel a large distance through the atmosphere to reach our eyes. So, most of the blue and other shorter wavelengths get removed due to scattering. Thus, the light reaching our eyes is rich in red colour. So the sun looks reddish at sunrise or sunset.

 

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