Ruben's Tube

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Description:

Rubens tube (ex airtrack) in action

A gas filled tube has a single row of small holes along the top at regular intervals. A speaker is attached to one end and the gas supply to another. A signal generator drives the speaker to create standing waves in the tube. The nodes and antinodes in the tube create variations in pressure in the gas escaping from the holes in the tube. When lit these produce a clear wave pattern along the top of the tube.

Background:
Although a classic physics experiment, most establishments may have abandoned their versions for “safer” alternatives. There are a few videos available on the internet (See external links below) that can easily be found using a search engine.

{{#ev:youtube|Ervj9wcAW4Q|300}} A working Youtube submitted by Mrs Fiona Watts, a science technician working at Haberdashers Askes Boys School in London

How to make one:
CLEAPSS members should read PS85A and PS85B. The following was posted before these and the content is only a suggestion.
It is easily possible for a technician to create one of these from a length of tubing. The most time consuming part is to drill 1 to 2mm holes in a straight line at regular intervals along the length of the tubing. A large region of non-drilled tube is recommended at each end. This will allow clamps to be used to keep the tube off the bench (and reduce the need for heatproof matting). The speaker should be of similar diameter to the tube although a cut down funnel may be used to marry larger speakers to the tube. The speakers should be sealed to the tube with tape to create a gas tight seal.

The following should be a legal method as it complies with SI 1998 2451 :"(6) Nothing in these Regulations shall apply in 
relation to - ... (b) the supply of gas to, or anything done in respect of, a bunsen burner used in an educational establishment; "

Requirements:

  • 2to 3m length of 20mm or 25mm diameter copper tubing (from DIY shops)
  • speaker from a headphone
  • End stop for above
  • 1.5mm drill bit
  • Pillar drill
  • "Vee" block and clamp
  • Drill bit and tap for a M10,1mm pitch thread
  • Bunsen burner
  • Tape or epoxy adhesive to secure speaker.


Method:

  1. Drill the center and tap the end stop.
  2. Mark the tube for drilling at 2cm intervals leaving 20cm free at both ends.
  3. Place in "Vee" block clamp and drill marked holes.
  4. Solder or tighten the drilled stop to one end of the pipe.
  5. Connect the speaker to the other end.
  6. Take the bunsen and unscrew the chimney.
  7. Screw the bunsen base to the end stop.
  8. Connect to the (bottled) gas supply.
  9. The above minimises waste gas due to the small volume.


The gas supply should be into the tube at the other end to the speaker and the point of 
entry sealed. It seems that if a Bunsen burner is used in the UK this is legal to be 
carried out! IT IS STRONGLY RECOMMENDED that you should check your local situation 
before creating a Ruben’s tube. Bottled gas is preffered to avoid legal conflicts.

See also:

If you have a defunct linear air track this can easily be adapted by sealing one side of holes with tape. Holes for legs etc also require sealing.

Precautions for use:
Caution.jpg This is a potentially dangerous piece of kit! However, the impact is well worth some simple precautions.

  • Check that no gas escapes from anywhere other than the small holes.
  • The holes should be mounted so that they are at the highest point of the tube.
  • Ensure that the room will be free for an hour after use (to clear fumes) and that the windows are able to be opened for ventilation.
  • A long length of rubber tubing is required so that the gas valve can be well away from the tube.
  • It is recommended that classes be kept 2m away from this kit and a second adult is present to take length measurements if required.
  • There should be clear access to fire blanket and gas valves/taps.


In common with any practical that you carry out in the Laboratory there should be a 
suitable and sufficient Risk assessment caried out by a competent person who is aware of 
the dangers of this experimet and who is in a position to take the necessary action to 
decide upon and implement whatever controls appropriate to minimise the hazards to 
the operator and students. You can always ring CLEAPSS for advice and help on the 
risk assessment.


Operational notes:
When first used the gas needs to fill the tube. Until the tube is filled the flames will be of poor quality as the combustible ratio needs to improve. The holes near the speaker may take a couple of minutes to achieve a good mix. Light the gas using a lighted splint reasonably soon after turning the gas on. Work from the supply end to the speaker. As soon as the majority of the jets are alight, turn on the signal generator. Use reasonably low volumes as the higher volumes may blow the jets out. Relight any jets that have no flames. Adjust the frequency to give different wave patterns. If required a cassette recorder or similar can be used to drive the speakers with music of a “son et lumiere” special. Keep the display short to avoid excessive heating of the tape joints.

Recommended adjuncts:
Chladni's Plates, Hoop of wire on a Vibration generator, Acoustic interferometer (Quinke’s apparatus), Newton’s rings


* Back to: Physics Experiments
* Back to: Physics


External Links


--D.B.Ferguson 22:10, 1 March 2007 (GMT)

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