A Rubens tube is a long metal pipe with holes along its top, filled with propane and lit to produce flames. When sound waves are introduced through a speaker at one end, the flames reveal the standing wave pattern inside the tube, making sound waves visible as a dynamic flame display.

1. Place the Rubens tube securely on stands with its mounts.
2. Connect the propane tank to the tube using the hose and fitting.
3. Position the speaker so it aligns with the silicone membrane at one end of the tube without touching it.
4. Attach the speaker to an amplifier or function generator using cables.
5. Open the propane valve and allow gas to flow into the tube.
6. Light the holes along the tube to create a row of flames, adjusting height with the valve.
7. Turn on the frequency generator and gradually change the frequency.
8. Observe how the flames rise and fall in patterns that match the standing waves inside the tube.

Ruben's Tube - Jared Ficklin:

Ruben's Tube Theory - Outreach, Chem Eng, Univ of Utah:

📄 Rubens Tube - UCSC Physics Demonstration Room: https://ucscphysicsdemo.sites.ucsc.edu/physics-5b6b-demos/rubens-tube/

• Use different sound sources (music, voice, or sine waves) to compare flame patterns.
• Test tubes of different lengths or diameters to explore changes in resonance.
• Replace propane with another safe gas to see how flame patterns differ.
• Use slow-motion video to capture the movement of the flames in detail.

• Only operate in a well-ventilated area to avoid gas buildup.
• Always have a fire extinguisher and fire blanket nearby.
• Wear a fire-resistant lab coat and safety goggles.
• Ensure the tube is securely mounted before lighting.
• Never allow flames near the propane tank or hoses.
• Turn off gas supply immediately after the demonstration.

• Why do the flames rise higher at some points and lower at others? (They follow the pressure variations of the standing wave, with more gas escaping at antinodes.)
• Why are only odd harmonics observed in the tube? (Because it acts as a closed-end tube with a displacement node at one end and an antinode at the other.)
• How could the speed of sound in propane be determined using this setup? (By measuring flame spacing for a known frequency and applying the wave equation.)
• What would change if the tube were open at both ends? (Even harmonics would also appear, altering the standing wave patterns.)