Standing Waves In Sound

Explained by a Rueben's Tube -Kyle Dubreuil

What is a Rubens Tube?

• A metal tube with holes evenly spaced along the top• Pumped full of flammable gas, then lit• Sound is then played into the tube• Differences in gas pressure caused by the sound create different

heights of flame (high at high pressure)• This allows the visualization of sound waves inside the tube

What Harmonic is the sound in this Rubens tube at? (assume both ends closed)• A.) 1st (Fundamental Frequency)• B.) 2nd• C.) 3rd• D.) 4th

Answer: C.) Third Harmonic

• The harmonic can be determined by counting the number of antinodes in a given length (L) of material• The high portions of flame correspond to antinodes • Counting these regions we see there are 3, therefore 3 antinodes,

showing that the sound inside the tube is at the 3rd harmonic• This also corresponds to a Mode of n=3

Given that this Rubens tube is 6m long, and the sound waves inside are travelling at 343m/s, what is the frequency and wavelength of this standing wave?

Answer:λ=4m, f=85.75Hz

• λ = 2L/3

• f = 3v/2L

• Using these two formulas and substituting the given values, one should find the correct answers as given above.

Materials Cited

• http://upload.wikimedia.org/wikipedia/commons/2/2b/Rubens_Tube_fire.jpg• http://i0.wp.com/TechAcute.com/wp-content/uploads/2014/05/rube

ns-tube-2d-Sune-Nielsen-Veritasium-concept-drawing-plan-visualizer-fire.jpg?resize=672%2C372• http://cdn.instructables.com/F4K/1LOM/F5Y3TML5/F4K1LOMF5Y3T

ML5.LARGE.jpg• http://www.flinnsci.com/store/catalogPhotos/AP7363cat.jpg