Lense and Image Formation

Light that is emitted from a surface, or reflected from it, leaves the surface in the form of spherical wavefronts. Every point on the surface can be thought of as a source of these wavefronts. Rather than drawing the wavefronts, we customarily illustrate the propagation of light with rays. These are just lines with arrowheads that point in the direction in which the light is traveling. Lenses are objects made from a transparent material such as glass that, because of the shape of their surfaces, alter the shape of the wavefronts, and, therefore, the direction of the rays of light passing through them. There are two basic types of lenses. These are: (1) Converging lenses that are thicker in the middle than at the edges and cause rays to converge more on the exit than on the entrance side of the lens, and diverging lenses that are thicker at the edges and cause rays to diverge more on the exit side.

The surfaces of lenses are usually small segments of large spheres. A line drawn through the centers of these spheres will also go through the center of the lens and is called