1H10.35 - Bend a Wall

See procedure
See procedure
See procedure
Code Number:
Demo Title:
Bend a Wall
Action & Reaction
Area of Study:
Laser, beam splitter, Radio shack speaker amplifier with photocell, mirror with magnetic backing, metal "wall".

See also 6D40.60 in Optics

Attach the magnet to the blackboard or metal wall.  Align the laser beam so that it is bounced back into the laser. Place the beam splitter in front of the laser and put the reflected beam onto the photocell.  Turn up the amplifier and then press on the wall or the table holding the apparatus.  A squeal should emit from the amplifier speaker as the wall or table flexes.

An simple version of this demo is to just shoot the laser beam directly into the photocell that is connected to the amplifier/speaker.  Place a microscope slide in the beam between the laser and the photocell.  As you rotate the microscope slide a "whine" will be heard from the speaker.

  • Chris R. Brown, "Optics Puzzler", TPT, Vol. 45, # 9, Dec. 2007, p. 571.
  • James M. Moses, K. P. Trout, "A Simple Laser Microphone for Classroom Demonstration", TPT, Vol. 44, # 9, Dec. 2006, p. 600.
  • Daniel L. Maclsaac and Michael Nordstrand, "Wall Flexure Correction", TPT, Vol. 23, # 6, Sept. 2001, p. 325. 
  • Daniel L. Maclsaac and Michael Nordstrand, "Demonstrating and Measuring the Flexure of a Masonry Wall", TPT, Vol. 39, # 4, Apr. 2001, p. 212 - 214.
  • Tung Jeong, Larry Alofs, "Hear the Wall Bend", TPT, Vol. 23, # 2, Feb. 1985, p. 108 - 110.
  • T. D. Nichols, D. C. Harrison, and S. S. Alpert, "Simple Laboratory Demonstration of the Doppler Shift of Laser Light", AJP, Vol. 53, #7, July 1985, p. 657.
  • R. E. Crandall and E. H. Wishnow, "Listening to the Doppler Shift of Visible Light", AJP, Vol. 49, #5, May 1981, p. 477.
  • Borislaw Bilash II, David Maiullo, "Push You, Push Me", A Demo a Day: A Year of Physics Demonstrations, p. 117.
  • Borislaw Bilash II, David Maiullo, "Lazy Walls", A Demo a Day: A Year of Physics Demonstrations, p. 6.
  • Richard E. Crandall, "Simple and Vivid Demonstrations of Advanced Concepts in Physics", The Amateur Scientist, Jan. 1983.

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