OP2.3 Lenses: Plane, Convex, Concave
This is a good demonstration of lenses. A box is screwed to the blackboard that has a light source. This source puts out five rays of white light via an arrangement of slits and mirrors. The direction of the rays can be changed by turning the knobs on the box. Using different lenses, the class can see that convex lenses are converging and concave ones are diverging. Arrangements of these can be made with the vast assortment of lenses (C53-4). Turning off the board lights enhances the audience's view. Another version is a laser used with lenses held in a circular apparatus. As the laser scrapes the edge of the lens, the different paths are easily seen. In order to understand the reason convex lenses converge and concave diverge, use a laser (locked cabinet), a water bath, and the hallow lenses in C64. The two sides of the lenses are separated by air and not glass, thus creating a transition from a higher index of refraction to a lower and then back to a higher, which is opposite of glass lenses in air. The convergent properties of these lenses are opposite to that of ordinary lenses.
Equipment Location: C24, C52