Demonstrations

Thin Lenses - Focal Points and Focal Lengths

Code Number :	6A60.49
Disclaimer:	Reprinted by permission of Dick Berg, University of Maryland, for use on this website. The demonstrations contained and referenced herein are listed for the purposes of cataloging and describing physics demonstrations which should be conducted only under the direction of a trained instructional support professional or physicist. These demonstrations are not presented for the purpose of being conducted by persons unconnected to this Facility and/or persons not consulting with or being supervised by the recognized instructional support professional or physicist and his/her staff. The University is responsible only for those demonstrations carried out using its own equipment using established safety and scheduling policies, and bears no responsibility for those choosing to use this source material for their own purposes. All demonstrations described and contained herein are public domain, and can also be found in reference materials in libraries, bookstores, and electronic sources. Further information regarding legal liability in use of demonstrations and labs will be found on the web site Injuries in School/College Laboratories in USA. The University of Iowa Disclaimers: University of Iowa Disclaimer All Rights Reserved..
Condition :	Good
Principle :	Lenses and Image Formation
Area of Study :	Optics
Equipment :	Slide Projector, lenses of various focal lengths, screen, video camera.
Procedure :	Set the slide projector so that it is at least 25 ft. away from the lens. Make sure the camera is focused well onto the screen. Turn on the projector and use the lens to bring the light to a small point as seen by the camera. Measure the distance from the lens to the screen. This is your focal length. Negative lenses may be used to show that no focal point can be produced.

References

Donald Russell Trummel, "Error in Determining Focal Length", TPT, Vol. 42, # 2, Feb. 2004, p. 123.

D.A. Crandles and R.P. Kauffman. "Locating Images Formed by Diverging Lenses." TPT, Vol. 35, # 6, p. 369, (Sept. 1997).

Steve Brown, "Finding the Focal Length of a Diverging Lens," TPT, Vol. 35, # 8, p. 452, (Nov. 1997).

Werner B. Schneider, "A Lens with an Adjustable Focal Length," TPT, Vol. 31, # 2, p. 118, (February 1993).

Simon George, "Focal Length of a Thin Lens Under Water", TPT, Vol. 16, # 6, Sept. 1978, p. 379.

Donald Russel Trummel, "Error in Determining Focal Length", TPT, Vol. 15, # 2, Feb. 1977, p. 112.

Fred M. Goldberg and Lillian C. McDermott, "An Investigation of Student Understanding of the Real Image Formed by Converging Lens or Concave Mirror," AJP, p. 108, Vol. 55, No. 2, (February 1987).

William S. Heaps, "How Not to Focus a Small Source with a Single Lens," AJP, p. 888, Vol. 55, No. 10, (October 1987).

Og-5, 6, 12: Freier and Anderson, "A Demonstration Handbook for Physics.

"Nodal Slide: A Study of the Properties of Thick Lenses", Selective Experiments in Physics, CENCO, 1962.

Mail Questions and Comments to: Dale Stille