Human Eye and Colourful World
The human eye is one of the most valuable and sensitive sense organs. It uses light and enables us to see beauty of world around us.
Human eye is like a camera lens, the focal length of which can be increased or decreased up to some extent. The ability of eye lens to adjust its focal length is called accommodation. To see or read an object it must be held at about 25cm from normal eyes. This is called least distance of distinct vision or near point of the eye. The farthest point up to which the eye can see an object clearly is called far point of eye and it is infinity for a normal eye.
With age the eye may gradually lose its power of accommodation and the person cannot see objects distinctly and comfortable. The vision becomes blurred due to refractive defects of eye. The three common refractive defects are (1) myopia or near-sightedness, (2) hypermetropia or far-sightedness, and (3) Presbyopia. These defects can be corrected by the use of suitable spherical lens.
Refraction of light not only takes place through lenses, but also through a prism. The incident light ray on a prism suffers two refractions, one going from air to glass and other going from glass to air. The path of light ray deviates on passing through a prism.
When white light passes through a glass prism, it splits into its constituent seven colors. This phenomenon is called dispersion of light. The seven colors are also seen in the formation of a rainbow. A rainbow is a beautiful natural phenomenon which can be seen after the rain shower. The light from the sun reflects and refracts through water droplets in the atmosphere and form a rainbow.
Due to the refraction of sunlight through Earth’s atmosphere, we are able to see the stars twinkle, advance sunrise and delayed sunset. The particles in atmosphere scatter the light giving rise to Tyndall effect, blue colour of sky, red color of Sun at sunrise and sunset.