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Code Number: 3B55.40
Demo Title: Interference - Quincke's Tube or Trombone
Condition: Excellent
Principle: Constructive & Destructive, Interference of Sound Waves
Area of Study: Oscillations & Acoustics
Equipment:
Trombone apparatus, wave generator, Quincke's Interference Tube.
Procedure:
The trombone is a simple way to show constructive and destructive interference. Hook the speaker in the trombone to a wave generator and set the frequency to about 1000 Hz. Pulling the slide on the trombone will cause the path length to change on one side of the apparatus, giving about 3 nodes and antinodes possible at this wavelength.
The Quincke's Interference tubes can be used with someone speaking into it or what is probably easier is to use it with a wave generator and speaker so that you get a constant tone.
One of the path lengths in the apparatus is approximately 50 cm longer than the other. At around 350 Hz this apparatus will give a destructive interference. By pinching off the long hose you can go from a node to an anti-node as seen on the oscilloscope. At about 520 Hz you get constructive interference. By pinching off the long hose here you will get a reduction on the size of the sine wave because of subtraction.
References:
- G.R. Davies, "Interference and Diffraction Corridor Demonstrations", TPT, Vol. 33, # 4, p. 244- 247, April 1995.
- Willard E. Singer, "Acoustical Interference Demonstration Apparatus", TPT, Vol. 3, # 6, Sept. 1965, p. 282.
- Grant O. Gale, "Constructive and Destructive Interference", AJP, Vol. 19, #5, May 1951, p. 321.
- Sg- 4: Freier and Anderson, A Demonstration Handbook for Physics