Some years ago I built a Rubens Tube out of a length of plastic guttering, and a speaker. The tube has holes drilled in it at regular intervals and a speaker fitted at one end. It is then flooded with methane from the lab supply and ignited. When music is played through the speaker the flames flicker in time to the pulses of sound energy passing through the gas.
Sound travels as a pressure wave through the gas and so areas of high pressure produce larger flames and lower pressure areas produce smaller flames. I only tested our device once and since we had not protected the plastic with metal foil the holes started to melt. Metal foil would have conducted heat away from the holes enough that we could have run it for longer without it catching fire. Also, slightly unfortunately, the speaker caught fire so the device had to be scrapped on Health & Safety grounds. I have subsequently bought a nicely made aluminium one, which disappointingly rarely catches fire.
There are very many examples on YouTube of other Rubens Tubes. I quite like the following because it is brief, made with a plastic tube like mine and the scientist has a great moustache.
The height of the flames represents the amplitude of the sound wave, the closeness of the peaks represents the frequency or wavelength.
Questions…
- The gas being burned is a hydrocarbon – what chemical products will be produced by the burning gas?
- What property of a sound is affected by (a) the wavelength and (b) the amplitude?
- What is the unit of frequency?
- The metal foil on the Rubens Tube conducts heat away. Suggest another physical property all metals share?
- What chemical property do all metal oxides share?
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