Demonstrations

Speed of Light - Microwave

Code Number :	6A01.39
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 :	Excellent
Principle :	Speed of Light
Area of Study :	Optics, Astronomy
Equipment :	Microwave oven, marshmallows, glass plate,
Procedure :	Make an array of marshmallows on the glass plate. Place them in the microwave for a few seconds until some of them begin to melt. Measure the distance between the "hot" spots (antinodes), or the "cold" spots (nodes). This measurement should be the 1/2 wavelength of the microwave ovens free space wavelength. (This should be close to 6.1 cm for the 1/2 wavelength or 12.2 cm for the wavelength of the microwaves from our oven). The frequency of the microwave should be written on the rear of the microwave oven. In our case this is 2450 MHz. With these a calculation of the speed of light should be possible.

References

John E. Beaver, "The Speed of Light with a Short-Wave Radio", TPT, Vol. 38, # 3, March 2000, p. 172.

Jouni Viiri, "Temperature Distribution in a Microwave Oven", TPT, Vol. 36, # 1, Jan. 1998, p. 48.

Robert H. Stauffer, Jr. "Finding the Speed of Light with Marshmallows - A Take-Home Lab", TPT, Vol. 35, # 4, April 1997, p. 231.

C. Swartz, "A Marshmallow Paradox", TPT, Vol. 35, # 6, Sept. 1997, p. 323.

Barbara S. Andereck, "Microwave Hot Spots", TPT, Vol. 28, # 9, Dec. 1990, p. 580.

Alistair Steyn-Ross and Alister Riddel, "Standing Waves in a Microwave Oven", TPT, Vol. 28, # 7, Oct. 1990, p. 474.

Michael C. Schroeder, Charles W. Smith, "Estimating the Speed of Light with a TV Set", TPT, Vol. 23, # 6, Sept. 1985, p. 360.

Cool Threads: Selections from TAP-L 2006, "Measuring the Speed of Light with Marshmallows", PIRA News, Vol. 20, # 1, p. 3, 2007.

Kerry Parker and Michael Vollmer, "Bad Food and Good Physics: The Development of Domestic Microwave Cookery", Physics Education, Vol. 39, (1), Jan. 2004, p. 82.

Mail Questions and Comments to: Dale Stille