In the previous chapter we have seen how light gets reflected when it is incident on a surface. Now let us see what happens when a ray of light traveling from one medium to another medium of different density.
It is a matter of common experience that a swimming pool appears to have less depth than its actual depth. Similarly a straight stick partly immersed in water appears to be bent at the surface of water. The above observations suggest that light changes its path as it passes from one medium to another. This change in the path of light is due to the fact that the velocity of light varies as it travels from one medium to another. Thus the deviation in the path of light when it passes from one medium to another medium of different density is called refraction.
Apparent Star Position due to Atmospheric Refraction
The twinkling of stars is due to atmospheric refraction of starlight. Since the atmosphere bends starlight towards the normal the apparent position of the star is slightly different from its actual position. Hence the star appears slightly higher than its actual position.
We have observed that the sun is visible at the horizon about 2 minutes before the actual sunrise, and about 2 minutes after the actual sunset. This is also because of atmospheric refraction.
Atmospheric Refraction at Sunrise and Sunset
