Demonstrations

Interference of Sound Waves - Rotating Platform, LED

Code Number :	3B55.10
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 :	Constructive & Destructive Interference of Sound Waves
Area of Study :	Acoustics
Equipment :	2 large speakers, amplifier, wave generator, LED mounted with Microphone.
Procedure :	Mount the two speakers on a moveable table so that the tweeters are 1 meter apart. The wave generator should be run at 1000 Hertz or more. LR 70 works best for this as it is a square room and therefore easy to set up a standing wave pattern. When the pattern is produced the students should be able to move their heads from side to side and detect the standing wave pattern. The LED mounted with the microphone is so that you can show where the nodal points are in a room, (The LED will light at the peaks and go out at the nodes).

References

James Strachan, "Destructive Interference Between Computer Speakers", TPT, Vol. 44, # 7, Oct. 2006, p. 473.

Burt Brody, "Destructive Interference with a Circular Saw Blade," TPT, Vol. 40, # 4, p. 250, (April 2002).

John D. McGervey, "Hands-on Physics for Less than a Dollar per Hand-Part III," TPT, Vol. 34, # 7, p. 448, (Oct. 1996).

Nilgun Sungar, "Teaching the Superposition of Waves," TPT, Vol. 34, # 4, p. 236, (April 1996).

Robert M. Williamson, "Some Standing Waves Aren't Quantized", TPT, Vol. 34, # 6, Sept. 1996, p. 326.

Robert G. Hunt, "Dancing to a Different Tune", TPT, Vol. 31, # 4, Apr. 1993, p. 206.

Thomas B. Greenslade, Jr., "The Acoustic Lens", TPT, Vol. 16, # 2, Feb. 1978, p. 100.

John E. Peterson, "A Low-Cost Audio Oscillator", TPT, Vol. 16, # 5, May 1978, p. 303.

Robert W. Schramm, "Using a Stereo Tape Recorder as a Demonstration Device", TPT, Vol. 12, # 3, March 1974, p. 172.

Mario Iona, "Error Analysis", TPT, Vol. 9, # 2, Feb. 1971, p. 62.

M. H. Teller, "Wave Interference, Using Transducers", TPT, Vol. 8, # 5, May 1970, p. 259.

David P. Koch, "Two -Source Interference Transparency", TPT, Vol. 7, # 2, Feb. 1969, p. 103.

Ralph Baierlein and Vacek Miglus, "Illustrating Double-Slit Interference: Yet Another Way." AJP, 857, Vol. 59, # 9, (September 1991).

W. N. Mathews Jr., "Superposition and Energy Conservation for Small Amplitude Mechanical Waves." AJP, p. 233, Vol. 54, # 3, (March 1986).

Haywood Blum, "Acoustic Interference Demonstration,", AJP, Vol. 42, # 5, May 1974, p. 413.

Sl- 2, 3: Freier and Anderson, A Demonstration Handbook for Physics.

W- 320: "Corrugated Roofing & Sew. Tape," DICK and RAE Physics Demo Notebook.

W- 330: "Two Speakers - Aluminum Rod," DICK and RAE Physics Demo Notebook.

"168, Where Does the Energy Go?" Christopher P. Jargodzki and Franklin Potter, Mad About Physics, p. 62, 206.

James Cunningham and Norman Herr, "Interference of Sound," Hands-on Physics Activities with Real Life Applications, p. 425.

Mail Questions and Comments to: Dale Stille