6A01.10 - Speed of Light

Code Number:
Demo Title:
Speed of Light
Speed of Light
Area of Study:
Optics, Astronomy
Modulated Laser, Metrologic Speed of Light/Laser Video Kit, Oscilloscope (Tektronix 2235), Cenco Speed of Light Apparatus.

The Cenco Speed of Light Unit is very easy and effective for use in the classroom.  Just plug the 15 cm cable between the transmitter and receiver to establish a baseline trace.  Then replace the 15 cm cable with the 20 m cable and observe the shift.  Time and units are read directly off the oscilloscope.

For use as a measure of the speed of light the metro logic kit is not very good for our situation because of the long setup time and long path length involved.  This unit is excellent for the transmission of audio and video signals however.

  • Arne Bewersdorff, David Weller, "Measuring the Speed of Light in Liquids with a Smartphone", TPT, Vol. 60, #6, Sept. 2022, p. 516.
  • Paul Hewitt, "Answer to April 2018 Figuring Physics", TPT, Vol. 56, #5, May 2018, p. 328.
  • Robert P. Bauman, "Wave Propagation", TPT, Vol. 39, #9, Dec. 2001, p. 545.
  • P. H. Hinrichsen and J. C. Crawford, "An Improved Metrologic Speed of Light Apparatus", TPT, Vol. 13, #8, Nov. 1975, p. 504.
  • C. Harry Knowles, "The Manufacturer Comments", TPT, Vol. 13, #8, Nov. 1975, p. 507.
  • George F. R. Ellis, Jean-Philippe Uzan, "c is the Speed of Light, Isn't It?", AJP, Vol. 73, #3, Mar. 2005, p. 240.
  • E. Gulmez, "Measuring the Speed of Light with a Fiber Optic Kit: An Undergraduate Experiment", AJP, Vol. 65, #7, July 1997, p. 614.
  • Joshua B. Diamond, "Comment on 'Why the Speed of Light is Reduced in a Transparent Medium' by Mary B. James and David J. Griffiths [Am. J. Phys. 60, 309-313 (1992)]", AJP, Vol. 63, #2, Feb. 1995, p. 179.
  • Mary B. James and David J. Griffiths, "Why the Speed of Light is Reduced in a Transparent Medium", AJP, Vol. 60, #4, Apr. 1992, p. 309.
  • J. Vanderkooy, M. J. Beccario, "An Inexpensive, Accurate Laboratory Determinatin of the Velocity of Light", AJP, Vol. 41, #2, Feb. 1973, p. 272.
  • James Cooke et al., "Direct Determination of the Speed of Light as a General Physics Laboratory Experiment", AJP, Vol. 36, #9, Sept. 1968, p. 847.
  • Richard Fitzgerarld, "Ultraslow Light Pulse Propagation Observed in Atoms-Both Cold and Hot", Physics Today, Vol. 52, #7, July 1999, p. 17. 
  • Julius Sumner Miller, Q169 & A169, Millergrams II – Some More Enchanting Questions for Enquiring Minds, p. 41 & 97.

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.