10th Class Science Human Eye and Colourful World The Human Eye and the Colourful World

The Human Eye and the colourful World

• The Human Eye

• The human eye is made of structures like cornea, iris, lens and retina, which allow refraction to take place and form images. Because of the presence of two eyes we have a binocular (3-D) vision..

• Persistence of vision It is a phenomenon where the brain continues to sense the image, even after the object has been removed. This illusion continues for a very short time (appr. 1/16th of a second).

• Power of accommodation of the eye

• The ability of an eye to focus the distant and nearby objects on the retina by changing the focal length of its lens is called the power of accommodation of the eye.

• Defects of vision are (i) Myopia (ii) Hypermetropia (iii) Astigmatism and (iv) Presbyopia

• Prism

A homogeneous, transparent and refracting medium bounded by two triangular bases and three lateral surfaces inclined to each other at an angle is called a prism.

• Dispersion of light

The phenomenon of the splitting of light into its component colours due to the differences in the refractive indices with the wavelength is called dispersion of light.

• Refraction of light through a prism

When a ray of light passes through a glass prism, refraction (or bending), of light occurs both, when it enters the prism as well as when it leaves the prism. Since the refracting surfaces of the prism are not parallel, therefore, the emergent ray and incident ray are not parallel to one another. The angle between incident ray and emergent ray is called angle of Deviation. The refractive index of the prism \[\mu =\frac{\sin {{i}_{1}}}{\sin {{r}_{1}}}=\frac{\sin {{i}_{2}}}{\sin {{r}_{2}}}\]

• Atmospheric refraction and optical phenomena The refraction of light caused by the earth's atmosphere having air-layers of varying optical densities is called atmospheric refraction. Some of the optical phenomena in nature which occur due to the atmospheric refraction of light are twinkling of stars and advanced sunrise and delayed sunset.

• Scattering of Light

Light is scattered when it falls on various types of suspended particles in its path. Depending on the size of the particles, the scattering can be of white sunlight as such or of the coloured lights which make up the white sunlight.

• Tyndall Effect is the scattering of light by particles in its path to make them visible.

• The sky is blue due to the scattering of blue component of the white sunlight by air molecules present in the atmosphere.

• The sun appears red at sunrise and sunset because at that time most of the blue colour present in the sunlight has been scattered away from our line of sight, leaving behind mainly red colour in the direct sunlight beam that reaches our eyes.