Speed of Light - Laser Diode



 

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 Code Number :   6A01.05  

Disclaimer:

Reprinted by permission of Dick Berg, University of Maryland, for use on this website.

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Condition :   Excellent  
Principle :   Speed of Light
Area of Study :  Optics, Astronomy  
Equipment :   Laser Diode pulser unit, corner cube, digital oscilloscope, laptop with Softscope interface, optics rail, meter tape measure, Plexiglas block.
Procedure :   Align the pulser unit and the corner cube when they are separated by a distance of 1.25 meters ( total path = 2.5 m ).  Either the digital scope or the laptop with interface can be used depending on what type of projection you want to do.  The digital scope usually has less noise when the corner cube is moved.  You will get a single rise curve for a single path and a double rise curve for the two paths.  The part of the curve to measure is the first full rise (time of the sent pulse and its return from the corner cube).  Both the digital scope and the laptop have cursers that can measure directly the time for that distance traveled.  

An interesting experiment to try is the measurement of the index of refraction of another medium such as Plexiglas.  Place the Plexiglas block into the light path and measure the change in the path time difference between the air and the Plexiglas. 

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   References

Robert P. Bauman, "Wave Propagation", TPT, Vol. 39, # 9, Dec. 2001, p. 545.

W. Larry Freeman, "The Velocity-of-Light Apparatus by PHYWE - An Evaluation", TPT, Vol. 35, # 5, May 1997, p. 295.

John E. Carlson, "Speed of Light Measurement with the Laser Pointer," TPT, Vol.  34, # 3, p. 176-177, (March 1996).

Allan Feldman, "The Speed of Light in Different Media", TPT, Vol. 29, # 2, Feb. 1991, p. 112.

"Heavy Conversation on a  Light Topic", TPT, Vol. 24, # 1, Jan. 1986, A Physics Student Newsletter, Vol. 1, # 1.

Mail Questions and Comments to:  Dale Stille