PURPOSE: To show a concave and a convex lens.
DESCRIPTION: Place the multiple ray project and lens on the board such that the light from the projector falls on the lens directly (see above pictures). Notice how the type of lens affects how the light behaves.
If the lens is convex (in other words, the surfaces of the lens bulge outward), a collimated beam of light traveling parallel to the lens axis will be converged or focused to a certain point along the axis, at a certain distance behind the lens. This distance is known as the focal length. The lens is therefore a converging lens.
If the lens is concave (where the surfaces of the lens bulge inward), a collimated beam of light traveling parallel to the lens axis is diverged. Therefore, we call this lens the diverging lens (how intuitive is physics? no need for that bulky textbook anymore...). The beam after passing through the lens appears to be emanating from a particular point on the axis in front of the lens. The distance between these two points is called the focal length.
EQUIPMENT: Multiple ray projector and lenses, as photographed. Portable white board.
SETUP TIME: 1/2 hour.
EXTERNAL WEB RESOURCES: Concave Lens Tutorial
REFERENCES: Lens (optics). (2007, June 20). In Wikipedia, The Free Encyclopedia. Retrieved 14:01, June 26, 2007, from http://en.wikipedia.org/w/index.php?title=Lens_%28optics%29&oldid=139440689
Updated by RR on 6/22/07