Refraction at Spherical Surfaces. Today’s agenda: Death Rays. You must know when to run from Death Rays. Refraction at Spherical Surfaces. You must be able to calculate properties of images formed by refraction at spherical surfaces. Thin Lenses: Concave and Convex Lenses, Ray Diagrams, Solving the Lens Equation. You must understand the differences between these two kinds of lenses, be able to draw ray diagrams for both kinds of lenses, and be able to solve the lens equation for both kinds of lenses. Lens Combinations, Optical Instruments. You should be aware of this useful information, which will not be presented in lecture.

Thin Lenses A lens in this section is taken to be a single object made of transparent material of refractive material n>1. There are two surface boundaries. Light from an object incident on the first surface forms an image, which becomes the object for the second surface. A thin lens is one for which the distance from the object to each of the two surfaces is the “same” (and the distance from the image to each surface is the “same”). This would NOT qualify as a thin lens.

I will make my lenses look “hollow,” like this. There are several surface combinations from which we can make lenses. Here are three (there are more).

Converging and Diverging Lenses Thin lenses can be converging or diverging. The converging lens is thicker in the center. The diverging lens is thicker at the edges. There are focal points on both sides of each lens. The focal length is the same whether light passes from left to right or right to left.

There are two surfaces at which light refracts There are two surfaces at which light refracts. Our equations (provided later) “automatically” take care of this. In your diagrams, simply draw the incident ray up to the center of the lens, then draw the refracted ray in its final direction.