6A60.49 - Thin Lenses - Focal Points and Focal Lengths

Code Number:
6A60.49
Demo Title:
Thin Lenses - Focal Points and Focal Lengths
Condition:
Good
Principle:
Lenses and Image Formation
Area of Study:
Optics

Disclaimer

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:
  • Yoong Sheng Phang, Yiping Zhao, "Determining the Focal Length of Converging and Diverging Lenses Using a Smartphone", TPT, Vol. 60, #8, Nov. 2022, p. 703.
  • Jun Wang, and Wenqing Sun, "Measuring the Focal Length of a Camera Lens in a Smart-Phone with a Ruler", TPT, Vol. 57, #1, Jan. 2019, p. 54.
  • Jair Lucio Prados Ribeiro, "A Glass of Wine a Day Does Not Keep Optics Away! Reflection and Refraction Images in Wine Glasses", TPT, Vol. 51, #8, Nov. 2013, p. 506.
  • Leos Dvorak, "A Do-It-Yourself Optical Bench", TPT, Vol. 49, #7, Oct. 2011, p. 452. 
  • Donald Russell Trummel, "Error in Determining Focal Length", TPT, Vol. 42, #2, Feb. 2004, p. 123.
  • Steve Brown, "Finding the Focal Length of a Diverging Lens", TPT, Vol. 35, #8, Nov. 1997, p. 452.
  • D.A. Crandles and R.P. Kauffman, "Locating Images Formed by Diverging Lenses", TPT, Vol. 35, #6, Sept. 1997, p. 369.
  • Werner B. Schneider, "A Lens with an Adjustable Focal Length", TPT, Vol. 31, #2, Feb. 1993, p. 118.
  • 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.
  • William S. Heaps, "How Not to Focus a Small Source with a Single Lens", AJP, Vol. 55, #10, Oct. 1987, p. 888.
  • Fred M. Goldberg and Lillian C. McDermott, "An Investigation of Student Understanding of the Real Image Formed by Converging Lens or Concave Mirror", AJP, Vol. 55, #2, Feb. 1987, p. 108.
  • M. M. Michaelis, "Laser Beam Guidance by Flames", AJP, Vol. 48, #11, Nov. 1980, p. 990.
  • Og-5, 6, 12: Freier and Anderson, A Demonstration Handbook for Physics.
  • Pat Murphy, Ellen Macaulay, and the staff of the Exploratorium, "Finding the Focal Length", Exploratopia, p. 296.
  • David Kutliroff, "13, Make an Air Lens", 101 Classroom Demonstrations and Experiments For Teaching Physics, p. 38.
  • Jearl Walker, "6.93, Starting A Fire With Ice", The Flying Circus of Physics Ed. 2, p. 278.
  • "Nodal Slide: A Study of the Properties of Thick Lenses", Selective Experiments in Physics, CENCO, 1962.
  • Julius Sumner Miller, Q226 & A226, Millergrams II – Some More Enchanting Questions for Enquiring Minds, p. 70 & 117.
  • Julius Sumner Miller, Q230 & A230, Millergrams II – Some More Enchanting Questions for Enquiring Minds, p. 72 & 118.

Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.