Rubens' Tube - AbsoluteAstronomy.com

The Rubens' tube, also known as the standing wave flame tube, or simply flame tube, is a physics

Physics

Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

experiment

Experiment

An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...

demonstrating a standing wave

Standing wave

In physics, a standing wave – also known as a stationary wave – is a wave that remains in a constant position.This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling...

. It shows the relationship between sound waves and sound pressure

Sound pressure

Sound pressure or acoustic pressure is the local pressure deviation from the ambient atmospheric pressure caused by a sound wave. Sound pressure can be measured using a microphone in air and a hydrophone in water...

Overview

A length of pipe is perforated along the top and sealed at both ends - one seal is attached to a small speaker or frequency generator, the other to a supply of a flammable gas (propane tank). The pipe is filled with the gas, and the gas leaking from the perforations is lit. If a suitable constant frequency is used, a standing wave can form within the tube. When the speaker is turned on, the standing wave will create points with oscillating (higher and lower) pressure and points with constant pressure (pressure nodes) along the tube. Where there is oscillating pressure due to the sound waves, less gas will escape from the perforations in the tube, and the flames will be lower at those points. At the pressure nodes, the flames are higher. At the end of the tube gas molecule velocity is zero and oscillating pressure is maximal, thus low flames are observed. It is possible to determine the wavelength from the flame minima and maxima by simply measuring with a ruler.

Explanation

Since the time averaged pressure is equal at all points of the tube, it is not straightforward to explain the different flame heights. The flame height is proportional to the gas flow as shown in the figure. Based on Bernoulli's principle

Bernoulli's principle

In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy...

, the gas flow is proportional to the square root of the pressure difference between the inside and outside of the tube. This is shown in the figure for a tube without standing sound wave. Based on this argument, the flame height depends non-linearly on the local, time-dependent pressure. The time average of the flow is reduced at the points with oscillating pressure and thus flames are lower.

History

John Le Conte

John Le Conte was an American scientist and academic. He served as President of the University of California, Berkeley.-Biography:...

discovered in 1858 that flames were sensitive to sound. In 1862 Rudolph Koenig

Rudolph Koenig

Karl Rudolph Koenig , known by himself and others as Rudolph Koenig, was a German physicist, chiefly concerned with acoustic phenomena.Koenig was born in Königsberg , and studied at the University of Königsberg in his native town....

showed that the height of a flame could be affected by transmitting sound in the gas supply, and the change as time passes could be displayed with rotating mirrors. August Kundt

August Kundt

August Adolf Eduard Eberhard Kundt was a German physicist.-Biography:Kundt was born at Schwerin in Mecklenburg. He began his scientific studies at Leipzig, but afterwards went to Berlin University. At first he devoted himself to astronomy, but coming under the influence of H. G...

, in 1866, demonstrated an acoustical standing wave

Standing wave

by placing seeds of lycopodium

Lycopodium

Lycopodium is a genus of clubmosses, also known as ground pines or creeping cedar, in the family Lycopodiaceae, a family of fern-allies...

or cork dust in a tube. When a sound was made in the tube, the material inside lined up in nodes

Node (physics)

A node is a point along a standing wave where the wave has minimal amplitude. For instance, in a vibrating guitar string, the ends of the string are nodes. By changing the position of the end node through frets, the guitarist changes the effective length of the vibrating string and thereby the...

and antinodes in line with the oscillation

Oscillation

Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...

of the wave, creating a standing wave. Later that century, Behn showed that small flames could be used as sensitive indicators of pressure. Finally, in 1904, using these two important discoveries, Heinrich Rubens

Heinrich Rubens

Heinrich Rubens was a German physicist.He played a direct role in the genesis of the quantum theory, providing the experimental results that pushed Max Planck to provide the first quantum hypothesis.He also combined scientific ideas to create the Rubens' tube.-External links:*...

, whom this experiment is named after, took a 4-metre-long tube and drilled 200 small holes into it at 2 centimeter intervals, and filled it with a flammable gas. After lighting the gas (whose flames all rose to near-equal heights), he noted that a sound produced at one end of the tube would create a standing wave, equivalent to the wavelength of the sound being made.
O. Krigar-Menzel assisted Rubens with the theory. A detailed theory of resonances in Rubens' Tube is given by Gardner et al.

Public displays

A Rubens' Tube was on display at The Exploratory in Bristol, England

Bristol

Bristol is a city, unitary authority area and ceremonial county in South West England, with an estimated population of 433,100 for the unitary authority in 2009, and a surrounding Larger Urban Zone with an estimated 1,070,000 residents in 2007...

until it closed in 1999, at which time the exhibit was moved to the @-Bristol museum.

This display is also found in Physics departments at a number of Universities.
A number of physics shows also have one, such as: Rino Foundation (The Netherlands), Fysikshow Aarhus (Denmark), Fizika Ekspres (Croatia) and ÅA Physics show (Finland).

The Mythbusters

MythBusters

MythBusters is a science entertainment TV program created and produced by Beyond Television Productions for the Discovery Channel. The series is screened by numerous international broadcasters, including Discovery Channel Australia, Discovery Channel Latin America, Discovery Channel Canada, Quest...

also included a demonstration on their "Voice Flame Extinguisher" episode in 2007.
The Daily Planet

Daily Planet

The Daily Planet is a fictional broadsheet newspaper in the , appearing mostly in the stories of Superman. The building's original features were based upon the AT&T Huron Road Building in Cleveland, Ohio...

's The Greatest Show Ever, ran a competition whereby five Canadian Science Centres competed for the best science centre's experiment/display. Edmonton's Science Centre (Telus World of Science) utilized a Rubens' Tube. In fact, the Rubens' Tube won the competition. The special was filmed on October 10, 2010.

External links

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.