Draw a diagram of dispersion of white light by the glass prism.

The splitting of white light into seven colours on passing through a transparent medium like a glass prism is called dispersion of light. The following diagram represents the dispersion of white light by the glass prism. The formation of the spectrum of seven colours shows that white light is made up of lights of seven different colours mixed together. The dispersion of white light takes place because the colours of white light travel at different speeds through a glass prism.

Draw a well labelled diagram of human eye.

The eye is one of our most important sense organs. The eye enables us to see the various objects around us. The main parts of the human eye are the cornea, iris, pupil, ciliary muscles, eye lens, retina and optic nerve. All these parts of the eye are shown in the following diagram. The cornea is the outermost part of the eye. Iris is found just behind the cornea. The pupil is the hole found in the middle part of the iris. The eye lens is found behind the pupil. It is a crystalline double convex lens made up of transparent, fibrous, soft and flexible jelly-like substance. Ciliary muscles hold the eye lens in position. The retina is a screen on which the image is formed in the eye. The nerve fibres coming from the retina are called the optic nerve.

What is hypermetropia? Give its causes. Explain with the help of a labelled ray diagram, how it is corrected.

The defect of the human eye in which a person can see the objects lying at long distances clearly, but cannot see the nearby objects distinctly is called hypermetropia. In a hypermetropic eye, the rays from the normal near point are focussed at a point beyond retina of the eye. The hypermetropic eye is caused by the following two defects: (i) Increase in the focal length of the eye lens (ii) The size of the eyeball becomes too short The following diagram represents a hypermetropic eye. To correct a hypermetropic eye, the person is allowed to wear spectacles with a convex lens of suitable power or focal length as indicated in the following figure. When a convex lens or converging lens of suitable power is placed in front of the hypermetropic eye, then the diverging rays of light coming from the nearby object are first converged by this convex lens. Thus, the convex lens forms a virtual image of the nearby object (lying at O ' ) at the point O of the hypermetropic eye which can be easily focused by the eye lens to form an image on the retina.